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Sample records for activity local field

  1. Influence of spiking activity on cortical local field potentials

    PubMed Central

    Waldert, Stephan; Lemon, Roger N; Kraskov, Alexander

    2013-01-01

    The intra-cortical local field potential (LFP) reflects a variety of electrophysiological processes including synaptic inputs to neurons and their spiking activity. It is still a common assumption that removing high frequencies, often above 300 Hz, is sufficient to exclude spiking activity from LFP activity prior to analysis. Conclusions based on such supposedly spike-free LFPs can result in false interpretations of neurophysiological processes and erroneous correlations between LFPs and behaviour or spiking activity. Such findings might simply arise from spike contamination rather than from genuine changes in synaptic input activity. Although the subject of recent studies, the extent of LFP contamination by spikes is unclear, and the fundamental problem remains. Using spikes recorded in the motor cortex of the awake monkey, we investigated how different factors, including spike amplitude, duration and firing rate, together with the noise statistic, can determine the extent to which spikes contaminate intra-cortical LFPs. We demonstrate that such contamination is realistic for LFPs with a frequency down to ∼10 Hz. For LFP activity below ∼10 Hz, such as movement-related potential, contamination is theoretically possible but unlikely in real situations. Importantly, LFP frequencies up to the (high-) gamma band can remain unaffected. This study shows that spike–LFP crosstalk in intra-cortical recordings should be assessed for each individual dataset to ensure that conclusions based on LFP analysis are valid. To this end, we introduce a method to detect and to visualise spike contamination, and provide a systematic guide to assess spike contamination of intra-cortical LFPs. PMID:23981719

  2. Active C4 Electrodes for Local Field Potential Recording Applications.

    PubMed

    Wang, Lu; Freedman, David; Sahin, Mesut; Ünlü, M Selim; Knepper, Ronald

    2016-01-01

    Extracellular neural recording, with multi-electrode arrays (MEAs), is a powerful method used to study neural function at the network level. However, in a high density array, it can be costly and time consuming to integrate the active circuit with the expensive electrodes. In this paper, we present a 4 mm × 4 mm neural recording integrated circuit (IC) chip, utilizing IBM C4 bumps as recording electrodes, which enable a seamless active chip and electrode integration. The IC chip was designed and fabricated in a 0.13 μm BiCMOS process for both in vitro and in vivo applications. It has an input-referred noise of 4.6 μV rms for the bandwidth of 10 Hz to 10 kHz and a power dissipation of 11.25 mW at 2.5 V, or 43.9 μW per input channel. This prototype is scalable for implementing larger number and higher density electrode arrays. To validate the functionality of the chip, electrical testing results and acute in vivo recordings from a rat barrel cortex are presented. PMID:26861324

  3. Active C4 Electrodes for Local Field Potential Recording Applications

    PubMed Central

    Wang, Lu; Freedman, David; Sahin, Mesut; Ünlü, M. Selim; Knepper, Ronald

    2016-01-01

    Extracellular neural recording, with multi-electrode arrays (MEAs), is a powerful method used to study neural function at the network level. However, in a high density array, it can be costly and time consuming to integrate the active circuit with the expensive electrodes. In this paper, we present a 4 mm × 4 mm neural recording integrated circuit (IC) chip, utilizing IBM C4 bumps as recording electrodes, which enable a seamless active chip and electrode integration. The IC chip was designed and fabricated in a 0.13 μm BiCMOS process for both in vitro and in vivo applications. It has an input-referred noise of 4.6 μVrms for the bandwidth of 10 Hz to 10 kHz and a power dissipation of 11.25 mW at 2.5 V, or 43.9 μW per input channel. This prototype is scalable for implementing larger number and higher density electrode arrays. To validate the functionality of the chip, electrical testing results and acute in vivo recordings from a rat barrel cortex are presented. PMID:26861324

  4. Unmasking local activity within local field potentials (LFPs) by removing distal electrical signals using independent component analysis

    PubMed Central

    Whitmore, Nathan W.; Lin, Shih-Chieh

    2016-01-01

    Local field potentials (LFPs) are commonly thought to reflect the aggregate dynamics in local neural circuits around recording electrodes. However, we show that when LFPs are recorded in awake behaving animals against a distal reference on the skull as commonly practiced, LFPs are significantly contaminated by non-local and non-neural sources arising from the reference electrode and from movement-related noise. In a data set with simultaneously recorded LFPs and electroencephalograms (EEGs) across multiple brain regions while rats perform an auditory oddball task, we used independent component analysis (ICA) to identify signals arising from electrical reference and from volume-conducted noise based on their distributed spatial pattern across multiple electrodes and distinct power spectral features. These sources of distal electrical signals collectively accounted for 23–77% of total variance in unprocessed LFPs, as well as most of the gamma oscillation responses to the target stimulus in EEGs. Gamma oscillation power was concentrated in volume-conducted noise and was tightly coupled with the onset of licking behavior, suggesting a likely origin of muscle activity associated with body movement or orofacial movement. The removal of distal signal contamination also selectively reduced correlations of LFP/EEG signals between distant brain regions but not within the same region. Finally, the removal of contamination from distal electrical signals preserved an event-related potential (ERP) response to auditory stimuli in the frontal cortex and also increased the coupling between the frontal ERP amplitude and neuronal activity in the basal forebrain, supporting the conclusion that removing distal electrical signals unmasked local activity within LFPs. Together, these results highlight the significant contamination of LFPs by distal electrical signals and caution against the straightforward interpretation of unprocessed LFPs. Our results provide a principled approach to

  5. Unmasking local activity within local field potentials (LFPs) by removing distal electrical signals using independent component analysis.

    PubMed

    Whitmore, Nathan W; Lin, Shih-Chieh

    2016-05-15

    Local field potentials (LFPs) are commonly thought to reflect the aggregate dynamics in local neural circuits around recording electrodes. However, we show that when LFPs are recorded in awake behaving animals against a distal reference on the skull as commonly practiced, LFPs are significantly contaminated by non-local and non-neural sources arising from the reference electrode and from movement-related noise. In a data set with simultaneously recorded LFPs and electroencephalograms (EEGs) across multiple brain regions while rats perform an auditory oddball task, we used independent component analysis (ICA) to identify signals arising from electrical reference and from volume-conducted noise based on their distributed spatial pattern across multiple electrodes and distinct power spectral features. These sources of distal electrical signals collectively accounted for 23-77% of total variance in unprocessed LFPs, as well as most of the gamma oscillation responses to the target stimulus in EEGs. Gamma oscillation power was concentrated in volume-conducted noise and was tightly coupled with the onset of licking behavior, suggesting a likely origin of muscle activity associated with body movement or orofacial movement. The removal of distal signal contamination also selectively reduced correlations of LFP/EEG signals between distant brain regions but not within the same region. Finally, the removal of contamination from distal electrical signals preserved an event-related potential (ERP) response to auditory stimuli in the frontal cortex and also increased the coupling between the frontal ERP amplitude and neuronal activity in the basal forebrain, supporting the conclusion that removing distal electrical signals unmasked local activity within LFPs. Together, these results highlight the significant contamination of LFPs by distal electrical signals and caution against the straightforward interpretation of unprocessed LFPs. Our results provide a principled approach to

  6. Effects of reconstructed magnetic field from sparse noisy boundary measurements on localization of active neural source.

    PubMed

    Shen, Hui-min; Lee, Kok-Meng; Hu, Liang; Foong, Shaohui; Fu, Xin

    2016-01-01

    Localization of active neural source (ANS) from measurements on head surface is vital in magnetoencephalography. As neuron-generated magnetic fields are extremely weak, significant uncertainties caused by stochastic measurement interference complicate its localization. This paper presents a novel computational method based on reconstructed magnetic field from sparse noisy measurements for enhanced ANS localization by suppressing effects of unrelated noise. In this approach, the magnetic flux density (MFD) in the nearby current-free space outside the head is reconstructed from measurements through formulating the infinite series solution of the Laplace's equation, where boundary condition (BC) integrals over the entire measurements provide "smooth" reconstructed MFD with the decrease in unrelated noise. Using a gradient-based method, reconstructed MFDs with good fidelity are selected for enhanced ANS localization. The reconstruction model, spatial interpolation of BC, parametric equivalent current dipole-based inverse estimation algorithm using reconstruction, and gradient-based selection are detailed and validated. The influences of various source depths and measurement signal-to-noise ratio levels on the estimated ANS location are analyzed numerically and compared with a traditional method (where measurements are directly used), and it was demonstrated that gradient-selected high-fidelity reconstructed data can effectively improve the accuracy of ANS localization. PMID:26358243

  7. Local field potential activity associated with temporal expectations in the macaque lateral intraparietal area.

    PubMed

    Premereur, Elsie; Vanduffel, Wim; Janssen, Peter

    2012-06-01

    Oscillatory brain activity is attracting increasing interest in cognitive neuroscience. Numerous EEG (magnetoencephalography) and local field potential (LFP) measurements have related cognitive functions to different types of brain oscillations, but the functional significance of these rhythms remains poorly understood. Despite its proven value, LFP activity has not been extensively tested in the macaque lateral intraparietal area (LIP), which has been implicated in a wide variety of cognitive control processes. We recorded action potentials and LFPs in area LIP during delayed eye movement tasks and during a passive fixation task, in which the time schedule was fixed so that temporal expectations about task-relevant cues could be formed. LFP responses in the gamma band discriminated reliably between saccade targets and distractors inside the receptive field (RF). Alpha and beta responses were much less strongly affected by the presence of a saccade target, however, but rose sharply in the waiting period before the go signal. Surprisingly, conditions without visual stimulation of the LIP-RF-evoked robust LFP responses in every frequency band--most prominently in those below 50 Hz--precisely time-locked to the expected time of stimulus onset in the RF. These results indicate that in area LIP, oscillations in the LFP, which reflect synaptic input and local network activity, are tightly coupled to the temporal expectation of task-relevant cues. PMID:22390466

  8. Local Field Potentials Encode Place Cell Ensemble Activation during Hippocampal Sharp Wave Ripples.

    PubMed

    Taxidis, Jiannis; Anastassiou, Costas A; Diba, Kamran; Koch, Christof

    2015-08-01

    Whether the activation of spiking cell ensembles can be encoded in the local field potential (LFP) remains unclear. We address this question by combining in vivo electrophysiological recordings in the rat hippocampus with realistic biophysical modeling, and explore the LFP of place cell sequence spiking ("replays") during sharp wave ripples. We show that multi-site perisomatic LFP amplitudes, in the ∼150-200 Hz frequency band, reliably reflect spatial constellations of spiking cells, embedded within non-spiking populations, and encode activation of local place cell ensembles during in vivo replays. We find spatiotemporal patterns in the LFP, which remain consistent between sequence replays, in conjunction with the ordered activation of place cell ensembles. Clustering such patterns provides an efficient segregation of replay events from non-replay-associated ripples. This work demonstrates how spatiotemporal ensemble spiking is encoded extracellularly, providing a window for efficient, LFP-based detection and monitoring of structured population activity in vivo. PMID:26247865

  9. Low-dimensional attractor for neural activity from local field potentials in optogenetic mice

    PubMed Central

    Oprisan, Sorinel A.; Lynn, Patrick E.; Tompa, Tamas; Lavin, Antonieta

    2015-01-01

    We used optogenetic mice to investigate possible nonlinear responses of the medial prefrontal cortex (mPFC) local network to light stimuli delivered by a 473 nm laser through a fiber optics. Every 2 s, a brief 10 ms light pulse was applied and the local field potentials (LFPs) were recorded with a 10 kHz sampling rate. The experiment was repeated 100 times and we only retained and analyzed data from six animals that showed stable and repeatable response to optical stimulations. The presence of nonlinearity in our data was checked using the null hypothesis that the data were linearly correlated in the temporal domain, but were random otherwise. For each trail, 100 surrogate data sets were generated and both time reversal asymmetry and false nearest neighbor (FNN) were used as discriminating statistics for the null hypothesis. We found that nonlinearity is present in all LFP data. The first 0.5 s of each 2 s LFP recording were dominated by the transient response of the networks. For each trial, we used the last 1.5 s of steady activity to measure the phase resetting induced by the brief 10 ms light stimulus. After correcting the LFPs for the effect of phase resetting, additional preprocessing was carried out using dendrograms to identify “similar” groups among LFP trials. We found that the steady dynamics of mPFC in response to light stimuli could be reconstructed in a three-dimensional phase space with topologically similar “8”-shaped attractors across different animals. Our results also open the possibility of designing a low-dimensional model for optical stimulation of the mPFC local network. PMID:26483665

  10. Spatial Representations in Local Field Potential Activity of Primate Anterior Intraparietal Cortex (AIP)

    PubMed Central

    Lehmann, Sebastian J.; Scherberger, Hansjörg

    2015-01-01

    The execution of reach-to-grasp movements in order to interact with our environment is an important subset of the human movement repertoire. To coordinate such goal-directed movements, information about the relative spatial position of target and effector (in this case the hand) has to be continuously integrated and processed. Recently, we reported the existence of spatial representations in spiking-activity of the cortical fronto-parietal grasp network (Lehmann & Scherberger 2013), and in particular in the anterior intraparietal cortex (AIP). To further investigate the nature of these spatial representations, we explored in two rhesus monkeys (Macaca mulatta) how different frequency bands of the local field potential (LFP) in AIP are modulated by grip type, target position, and gaze position, during the planning and execution of reach-to-grasp movements. We systematically varied grasp type, spatial target, and gaze position and found that both spatial and grasp information were encoded in a variety of frequency bands (1–13Hz, 13–30Hz, 30–60Hz, and 60–100Hz, respectively). Whereas the representation of grasp type strongly increased towards and during movement execution, spatial information was represented throughout the task. Both spatial and grasp type representations could be readily decoded from all frequency bands. The fact that grasp type and spatial (reach) information was found not only in spiking activity, but also in various LFP frequency bands of AIP, might significantly contribute to the development of LFP-based neural interfaces for the control of upper limb prostheses. PMID:26554592

  11. Activity in galactic nuclei of cluster and field galaxies in the local universe

    NASA Astrophysics Data System (ADS)

    Hwang, H. S.; Park, C.; Elbaz, D.; Choi, Y.-Y.

    2012-02-01

    Aims: We study the environmental effects on the activity in galactic nuclei by comparing galaxies in clusters and in the field. Methods: Using a spectroscopic sample of galaxies in Abell clusters from the Sloan Digital Sky Survey Data Release 7, we investigate the dependence of nuclear activity on the physical parameters of clusters as well as the nearest neighbor galaxy. We also compare galaxy properties between active galactic nuclei (AGNs) hosts and non-AGN galaxies. Results: We find that the AGN fraction of early-type galaxies starts to decrease around one virial radius of clusters (r200,cl) as decreasing clustercentric radius, while that of late types starts to decrease close to the cluster center (R ~ 0.1-0.5r200,cl). The AGN fractions of early-type cluster galaxies, on average, are found to be lower than those of early-type field galaxies by a factor ~3. However, the mean AGN fractions of late-type cluster galaxies are similar to those of late-type field galaxies. The AGN fraction of early-type brightest cluster galaxies lies between those of other early-type, cluster and field galaxies with similar luminosities. In the field, the AGN fraction is strongly dependent on the morphology of and the distance to the nearest neighbor galaxy. We find an anti-correlation between the AGN fraction and the velocity dispersion of clusters for all subsamples divided by morphology and luminosity of host galaxies. The AGN power indicated by L [OIII] /MBH is found to depend strongly on the mass of host galaxies rather than the clustercentric radius. The difference in physical parameters such as luminosity, (u - r) colors, star formation rates, and (g - i) color gradients between AGN hosts and non-AGN galaxies is seen for both early and late types at all clustercentric radii, while the difference in structure parameters between the two is significant only for late types. Conclusions: These results support the idea that the activity in galactic nuclei is triggered through

  12. Macroscopic Models of Local Field Potentials and the Apparent 1/f Noise in Brain Activity

    PubMed Central

    Bédard, Claude; Destexhe, Alain

    2009-01-01

    The power spectrum of local field potentials (LFPs) has been reported to scale as the inverse of the frequency, but the origin of this 1/f noise is at present unclear. Macroscopic measurements in cortical tissue demonstrated that electric conductivity (as well as permittivity) is frequency-dependent, while other measurements failed to evidence any dependence on frequency. In this article, we propose a model of the genesis of LFPs that accounts for the above data and contradictions. Starting from first principles (Maxwell equations), we introduce a macroscopic formalism in which macroscopic measurements are naturally incorporated, and also examine different physical causes for the frequency dependence. We suggest that ionic diffusion primes over electric field effects, and is responsible for the frequency dependence. This explains the contradictory observations, and also reproduces the 1/f power spectral structure of LFPs, as well as more complex frequency scaling. Finally, we suggest a measurement method to reveal the frequency dependence of current propagation in biological tissue, and which could be used to directly test the predictions of this formalism. PMID:19348744

  13. Ictal onset patterns of local field potentials, high frequency oscillations, and unit activity in human mesial temporal lobe epilepsy

    PubMed Central

    Weiss, Shennan Aibel; Alvarado-Rojas, Catalina; Bragin, Anatol; Behnke, Eric; Fields, Tony; Fried, Itzhak; Engel, Jerome; Staba, Richard

    2016-01-01

    Summary Objective To characterize local field potentials, high frequency oscillations, and single unit firing patterns in microelectrode recordings of human limbic onset seizures. Methods Wide bandwidth local field potential recordings were acquired from microelectrodes implanted in mesial temporal structures during spontaneous seizures from six patients with mesial temporal lobe epilepsy. Results In the seizure onset zone, distinct epileptiform discharges were evident in the local field potential prior to the time of seizure onset in the intracranial EEG. In all three seizures with hypersynchronous (HYP) seizure onset, fast ripples with incrementally increasing power accompanied epileptiform discharges during the transition to the ictal state (p < 0.01). In a single low voltage fast (LVF) onset seizure a triad of evolving HYP LFP discharges, increased single unit activity, and fast ripples of incrementally increasing power were identified ~20 s prior to seizure onset (p < 0.01). In addition, incrementally increasing fast ripples occurred after seizure onset just prior to the transition to LVF activity (p < 0.01). HYP onset was associated with an increase in fast ripple and ripple rate (p < 0.05) and commonly each HYP discharge had a superimposed ripple followed by a fast ripple. Putative excitatory and inhibitory single units could be distinguished during limbic seizure onset, and heterogeneous shifts in firing rate were observed during LVF activity. Significance Epileptiform activity is detected by microelectrodes before it is detected by depth macroelectrodes, and the one clinically identified LVF ictal onset was a HYP onset at the local level. Patterns of incrementally increasing fast ripple power are consistent with observations in rats with experimental hippocampal epilepsy, suggesting that limbic seizures arise when small clusters of synchronously bursting neurons increase in size, coalesce, and reach a critical mass for propagation. PMID:26611159

  14. Single-unit activity, threshold crossings, and local field potentials in motor cortex differentially encode reach kinematics.

    PubMed

    Perel, Sagi; Sadtler, Patrick T; Oby, Emily R; Ryu, Stephen I; Tyler-Kabara, Elizabeth C; Batista, Aaron P; Chase, Steven M

    2015-09-01

    A diversity of signals can be recorded with extracellular electrodes. It remains unclear whether different signal types convey similar or different information and whether they capture the same or different underlying neural phenomena. Some researchers focus on spiking activity, while others examine local field potentials, and still others posit that these are fundamentally the same signals. We examined the similarities and differences in the information contained in four signal types recorded simultaneously from multielectrode arrays implanted in primary motor cortex: well-isolated action potentials from putative single units, multiunit threshold crossings, and local field potentials (LFPs) at two distinct frequency bands. We quantified the tuning of these signal types to kinematic parameters of reaching movements. We found 1) threshold crossing activity is not a proxy for single-unit activity; 2) when examined on individual electrodes, threshold crossing activity more closely resembles LFP activity at frequencies between 100 and 300 Hz than it does single-unit activity; 3) when examined across multiple electrodes, threshold crossing activity and LFP integrate neural activity at different spatial scales; and 4) LFP power in the "beta band" (between 10 and 40 Hz) is a reliable indicator of movement onset but does not encode kinematic features on an instant-by-instant basis. These results show that the diverse signals recorded from extracellular electrodes provide somewhat distinct and complementary information. It may be that these signal types arise from biological phenomena that are partially distinct. These results also have practical implications for harnessing richer signals to improve brain-machine interface control. PMID:26133797

  15. A biophysically detailed model of neocortical Local Field Potentials predicts the critical role of active membrane currents

    PubMed Central

    Reimann, Michael W.; Anastassiou, Costas A.; Perin, Rodrigo; Hill, Sean; Markram, Henry; Koch, Christof

    2013-01-01

    Summary Brain activity generates extracellular voltage fluctuations recorded as local field potentials (LFPs). While known that the relevant micro-variables, the ionic currents across membranes, jointly generate the macro-variables, the extracellular voltage, neither the detailed biophysical knowledge nor the required computational power has been available to model these processes. We simulated the LFP in a model of the rodent neocortical column composed of >12,000 reconstructed, multi-compartmental and spiking cortical layer 4 and 5 pyramidal neurons and basket cells, including five million dendritic and somatic compartments with voltage- and ion-dependent currents, realistic connectivity and probabilistic AMPA, NMDA and GABA synapses. We found that, depending on a number of factors, the LFP reflects local and cross-layer processing and active currents dominate the generation of LFPs rather than synaptic ones. Spike-related currents impact the LFP not only at higher frequencies but lower than 50 Hz. This work calls for re-evaluating the genesis of LFPs. PMID:23889937

  16. Active control of Type-I Edge-Localized Modes with n=1 Perturbation Fields in the JET Tokamak

    SciTech Connect

    Liang, Y.; Koslowski, R.; Thomas, P.; Nardon, E.; Alper, B.; Baranov, Y.; Beurskens, M.; Bigi, M.; Crombe, K.; de la Luna, E.; De Vries, P.; Fundamenski, W.; Rachlew, Elisabeth G; Zimmermann, O.

    2007-06-01

    Type-I edge-localized modes (ELMs) have been mitigated at the JET tokamak using a static external n=1 perturbation field generated by four error field correction coils located far from the plasma. During the application of the n=1 field the ELM frequency increased by a factor of 4 and the amplitude of the D signal decreased. The energy loss per ELM normalized to the total stored energy, W/W, dropped to values below 2%. Transport analyses shows no or only a moderate (up to 20%) degradation of energy confinement time during the ELM mitigation phase.

  17. Indoor localization using magnetic fields

    NASA Astrophysics Data System (ADS)

    Pathapati Subbu, Kalyan Sasidhar

    Indoor localization consists of locating oneself inside new buildings. GPS does not work indoors due to multipath reflection and signal blockage. WiFi based systems assume ubiquitous availability and infrastructure based systems require expensive installations, hence making indoor localization an open problem. This dissertation consists of solving the problem of indoor localization by thoroughly exploiting the indoor ambient magnetic fields comprising mainly of disturbances termed as anomalies in the Earth's magnetic field caused by pillars, doors and elevators in hallways which are ferromagnetic in nature. By observing uniqueness in magnetic signatures collected from different campus buildings, the work presents the identification of landmarks and guideposts from these signatures and further develops magnetic maps of buildings - all of which can be used to locate and navigate people indoors. To understand the reason behind these anomalies, first a comparison between the measured and model generated Earth's magnetic field is made, verifying the presence of a constant field without any disturbances. Then by modeling the magnetic field behavior of different pillars such as steel reinforced concrete, solid steel, and other structures like doors and elevators, the interaction of the Earth's field with the ferromagnetic fields is described thereby explaining the causes of the uniqueness in the signatures that comprise these disturbances. Next, by employing the dynamic time warping algorithm to account for time differences in signatures obtained from users walking at different speeds, an indoor localization application capable of classifying locations using the magnetic signatures is developed solely on the smart phone. The application required users to walk short distances of 3-6 m anywhere in hallway to be located with accuracies of 80-99%. The classification framework was further validated with over 90% accuracies using model generated magnetic signatures representing

  18. Decoding 3D reach and grasp from hybrid signals in motor and premotor cortices: spikes, multiunit activity, and local field potentials

    PubMed Central

    Truccolo, Wilson; Vargas-Irwin, Carlos E.; Donoghue, John P.

    2012-01-01

    Neural activity in motor cortex during reach and grasp movements shows modulations in a broad range of signals from single-neuron spiking activity (SA) to various frequency bands in broadband local field potentials (LFPs). In particular, spatiotemporal patterns in multiband LFPs are thought to reflect dendritic integration of local and interareal synaptic inputs, attentional and preparatory processes, and multiunit activity (MUA) related to movement representation in the local motor area. Nevertheless, the relationship between multiband LFPs and SA, and their relationship to movement parameters and their relative value as brain-computer interface (BCI) control signals, remain poorly understood. Also, although this broad range of signals may provide complementary information channels in primary (MI) and ventral premotor (PMv) areas, areal differences in information have not been systematically examined. Here, for the first time, the amount of information in SA and multiband LFPs was compared for MI and PMv by recording from dual 96-multielectrode arrays while monkeys made naturalistic reach and grasp actions. Information was assessed as decoding accuracy for 3D arm end point and grip aperture kinematics based on SA or LFPs in MI and PMv, or combinations of signal types across areas. In contrast with previous studies with ≤16 simultaneous electrodes, here ensembles of >16 units (on average) carried more information than multiband, multichannel LFPs. Furthermore, reach and grasp information added by various LFP frequency bands was not independent from that in SA ensembles but rather typically less than and primarily contained within the latter. Notably, MI and PMv did not show a particular bias toward reach or grasp for this task or for a broad range of signal types. For BCIs, our results indicate that neuronal ensemble spiking is the preferred signal for decoding, while LFPs and combined signals from PMv and MI can add robustness to BCI control. PMID:22157115

  19. Gradual emergence of spontaneous correlated brain activity during fading of general anesthesia in rats: Evidences from fMRI and local field potentials

    PubMed Central

    Bettinardi, Ruggero G.; Tort-Colet, Núria; Ruiz-Mejias, Marcel; Sanchez-Vives, Maria V.; Deco, Gustavo

    2015-01-01

    Intrinsic brain activity is characterized by the presence of highly structured networks of correlated fluctuations between different regions of the brain. Such networks encompass different functions, whose properties are known to be modulated by the ongoing global brain state and are altered in several neurobiological disorders. In the present study, we induced a deep state of anesthesia in rats by means of a ketamine/medetomidine peritoneal injection, and analyzed the time course of the correlation between the brain activity in different areas while anesthesia spontaneously decreased over time. We compared results separately obtained from fMRI and local field potentials (LFPs) under the same anesthesia protocol, finding that while most profound phases of anesthesia can be described by overall sparse connectivity, stereotypical activity and poor functional integration, during lighter states different frequency-specific functional networks emerge, endowing the gradual restoration of structured large-scale activity seen during rest. Noteworthy, our in vivo results show that those areas belonging to the same functional network (the default-mode) exhibited sustained correlated oscillations around 10 Hz throughout the protocol, suggesting the presence of a specific functional backbone that is preserved even during deeper phases of anesthesia. Finally, the overall pattern of results obtained from both imaging and in vivo-recordings suggests that the progressive emergence from deep anesthesia is reflected by a corresponding gradual increase of organized correlated oscillations across the cortex. PMID:25804643

  20. Local Discontinuous Galerkin (LDG) Method for Advection of Active Compositional Fields with Discontinuous Boundaries: Demonstration and Comparison with Other Methods in the Mantle Convection Code ASPECT

    NASA Astrophysics Data System (ADS)

    He, Y.; Billen, M. I.; Puckett, E. G.

    2015-12-01

    Flow in the Earth's mantle is driven by thermo-chemical convection in which the properties and geochemical signatures of rocks vary depending on their origin and composition. For example, tectonic plates are composed of compositionally-distinct layers of crust, residual lithosphere and fertile mantle, while in the lower-most mantle there are large compositionally distinct "piles" with thinner lenses of different material. Therefore, tracking of active or passive fields with distinct compositional, geochemical or rheologic properties is important for incorporating physical realism into mantle convection simulations, and for investigating the long term mixing properties of the mantle. The difficulty in numerically advecting fields arises because they are non-diffusive and have sharp boundaries, and therefore require different methods than usually used for temperature. Previous methods for tracking fields include the marker-chain, tracer particle, and field-correction (e.g., the Lenardic Filter) methods: each of these has different advantages or disadvantages, trading off computational speed with accuracy in tracking feature boundaries. Here we present a method for modeling active fields in mantle dynamics simulations using a new solver implemented in the deal.II package that underlies the ASPECT software. The new solver for the advection-diffusion equation uses a Local Discontinuous Galerkin (LDG) algorithm, which combines features of both finite element and finite volume methods, and is particularly suitable for problems with a dominant first-order term and discontinuities. Furthermore, we have applied a post-processing technique to insure that the solution satisfies a global maximum/minimum. One potential drawback for the LDG method is that the total number of degrees of freedom is larger than the finite element method. To demonstrate the capabilities of this new method we present results for two benchmarks used previously: a falling cube with distinct buoyancy and

  1. [Field Learning Activities].

    ERIC Educational Resources Information Center

    Nolde Forest Environmental Education Center, Reading, PA.

    Seventy field activities, pertinent to outdoor, environmental studies, are described in this compilation. Designed for elementary and junior high school students, the activities cover many discipline areas--science, social studies, language arts, health, history, mathematics, and art--and many are multidisciplinary in use. Topics range from soil…

  2. Columnar specificity of microvascular oxygenation and blood flow response in primary visual cortex: evaluation by local field potential and spiking activity.

    PubMed

    Wang, Zheng; Roe, Anna W

    2012-01-01

    The relation of cortical microcirculation, oxygen metabolism, and underlying neuronal network activity remains poorly understood. Anatomical distribution of cortical microvasculature and its relationship to cortical functional domains suggests that functional organizations may be revealed by mapping cerebral blood flow responses. However, there is little direct experimental evidence and a lack of electrophysiological evaluation. In this study, we mapped ocular-dominance columns in primary visual cortex (V1) of anesthetized macaques with capillary flow-based laser speckle contrast imaging and deoxyhemoglobin-based intrinsic optical imaging. In parallel, the local field potentials (LFPs) and spikes were recorded from a linear array of eight microelectrodes, carefully positioned into left and right eye columns in V1. We found differential activation maps of blood flow, after masking large superficial draining vessels, exhibited a column-like pattern similar as the oximetric maps. Both the activated spikes and γ-band LFP demonstrated corresponding eye preference, consistent with the imaging maps. Our results present direct support in favor of previous proposals that the regulation of microcirculation can be as fine as the submillimeter scale, suggesting that cortical vasculature is functionally organized at the columnar level in a manner appropriate for supplying energy demands of functionally specific neuronal populations. PMID:22027939

  3. Distinct temporal spike and local field potential activities in the thalamic parafascicular nucleus of parkinsonian rats during rest and limb movement.

    PubMed

    Wang, Min; Qu, Qingyang; He, Tingting; Li, Min; Song, Zhimin; Chen, Feiyu; Zhang, Xiao; Xie, Jinlu; Geng, Xiwen; Yang, Maoquan; Wang, Xiusong; Lei, Chengdong; Hou, Yabing

    2016-08-25

    Several studies have suggested that the thalamic centromedian-parafascicular (CM/PF or the PF in rodents) is implicated in the pathophysiology of Parkinson's disease (PD). However, inconsistent changes in the neuronal firing rate and pattern have been reported in parkinsonian animals. To investigate the impact of a dopaminergic cell lesion on PF extracellular discharge in behaving rats, the PF neural activities in the spike and local field potential (LFP) were recorded in unilaterally 6-hydroxydopamine- (6-OHDA) lesioned and neurologically intact control rats during rest and limb movement. During rest, the two PF neuronal subtypes was less spontaneously active, with no difference in the spike firing rates between the control and lesioned rats; only the lesioned rats reshaped their spike firing pattern. Furthermore, the simultaneously recorded LFP in the lesioned rats exhibited a significant increase in power at 12-35 and 35-70Hz and a decrease in power at 0.7-12Hz. During the execution of a voluntary movement, two subtypes of PF neurons were identified by a rapid increase in the discharge activity in both the control and lesioned rats. However, dopamine lesioning was associated with a decrease in neuronal spiking fire rate and reshaping in the firing pattern in the PF. The simultaneously recorded LFP activity exhibited a significant increase in power at 12-35Hz and a decrease in power at 0.7-12Hz compared with the control rats. These findings indicate that 6-OHDA induces modifications in PF spike and LFP activities in rats during rest and movement and suggest that PF dysfunction may be an important contributor to the pathophysiology of parkinsonian motor impairment. PMID:27238892

  4. Adaptive autoregressive identification with spectral power decomposition for studying movement-related activity in scalp EEG signals and basal ganglia local field potentials

    NASA Astrophysics Data System (ADS)

    Foffani, Guglielmo; Bianchi, Anna M.; Priori, Alberto; Baselli, Giuseppe

    2004-09-01

    We propose a method that combines adaptive autoregressive (AAR) identification and spectral power decomposition for the study of movement-related spectral changes in scalp EEG signals and basal ganglia local field potentials (LFPs). This approach introduces the concept of movement-related poles, allowing one to study not only the classical event-related desynchronizations (ERD) and synchronizations (ERS), which correspond to modulations of power, but also event-related modulations of frequency. We applied the method to analyze movement-related EEG signals and LFPs contemporarily recorded from the sensorimotor cortex, the globus pallidus internus (GPi) and the subthalamic nucleus (STN) in a patient with Parkinson's disease who underwent stereotactic neurosurgery for the implant of deep brain stimulation (DBS) electrodes. In the AAR identification we compared the whale and the exponential forgetting factors, showing that the whale forgetting provides a better disturbance rejection and it is therefore more suitable to investigate movement-related brain activity. Movement-related power modulations were consistent with previous studies. In addition, movement-related frequency modulations were observed from both scalp EEG signals and basal ganglia LFPs. The method therefore represents an effective approach to the study of movement-related brain activity.

  5. Activation of D2 autoreceptors alters cocaine-induced locomotion and slows down local field oscillations in the rat ventral tegmental area.

    PubMed

    Koulchitsky, Stanislav; Delairesse, Charlotte; Beeken, Thom; Monteforte, Alexandre; Dethier, Julie; Quertemont, Etienne; Findeisen, Rolf; Bullinger, Eric; Seutin, Vincent

    2016-09-01

    Psychoactive substances affecting the dopaminergic system induce locomotor activation and, in high doses, stereotypies. Network mechanisms underlying the shift from an active goal-directed behavior to a "seemingly purposeless" stereotypic locomotion remain unclear. In the present study we sought to determine the relationships between the behavioral effects of dopaminergic drugs and their effects on local field potentials (LFPs), which were telemetrically recorded within the ventral tegmental area (VTA) of freely moving rats. We used the D2/D3 agonist quinpirole in a low, autoreceptor-selective (0.1 mg/kg, i.p.) and in a high (0.5 mg/kg, i.p.) dose, and a moderate dose of cocaine (10 mg/kg, i.p.). In the control group, power spectrum analysis revealed a prominent peak of LFP power in the theta frequency range during active exploration. Cocaine alone stimulated locomotion, but had no significant effect on the peak of the LFP power. In contrast, co-administration of low dose quinpirole with cocaine markedly altered the pattern of locomotion, from goal-directed exploratory behavior to recurrent motion resembling locomotor stereotypy. This behavioral effect was accompanied by a shift of the dominant theta power toward a significantly lower (by ∼15%) frequency. High dose quinpirole also provoked an increased locomotor activity with signs of behavioral stereotypies, and also induced a shift of the dominant oscillation frequency toward the lower range. These results demonstrate a correlation between the LFP oscillation frequency within the VTA and a qualitative aspect of locomotor behavior, perhaps due to a variable level of coherence of this region with its input or output areas. PMID:27130904

  6. Improvement of neurofeedback therapy for improved attention through facilitation of brain activity using local sinusoidal extremely low frequency magnetic field exposure.

    PubMed

    Zandi Mehran, Yasaman; Firoozabadi, Mohammad; Rostami, Reza

    2015-04-01

    Traditional neurofeedback (NF) is a training approach aimed at altering brain activity using electroencephalography (EEG) rhythms as feedback. In NF training, external factors such as the subjects' intelligence can have an effect. In contrast, a low-energy NF system (LENS) does not require conscious effort from the subject, which results in fewer attendance sessions. However, eliminating the subject role seems to eliminate an important part of the NF system. This study investigated the facilitating effect on the theta-to-beta ratio from NF training, using a local sinusoidal extremely low frequency magnetic field (LSELF-MF) versus traditional NF. Twenty-four healthy, intelligent subjects underwent 10 training sessions to enhance beta (15-18 Hz), and simultaneously inhibit theta (4-7 Hz) and high beta (22-30 Hz) activity, at the Cz point in a 3-boat-race video game. Each session consisted of 3 statuses, PRE, DURING, and POST. In the DURING status, the NF training procedure lasted 10 minutes. Subjects were led to believe that they would be exposed to a magnetic field during NF training; however, 16 of the subjects who were assigned to the experimental group were really exposed to 45 Hz-360 µT LSELF-MF at Cz. For the 8 other subjects, only the coil was located at the Cz point with no exposure. The duty cycle of exposure was 40% (2-second exposure and 3-second pause). The results show that the theta-to-beta ratio in the DURING status of each group differs significantly from the PRE and POST statuses. Between-group analysis shows that the theta-to-beta ratio in the DURING status of the experimental group is significantly (P < .001) lower than in the sham group. The result shows the effect of LSELF-MF on NF training. PMID:24939868

  7. Receptive Field Inference with Localized Priors

    PubMed Central

    Park, Mijung; Pillow, Jonathan W.

    2011-01-01

    The linear receptive field describes a mapping from sensory stimuli to a one-dimensional variable governing a neuron's spike response. However, traditional receptive field estimators such as the spike-triggered average converge slowly and often require large amounts of data. Bayesian methods seek to overcome this problem by biasing estimates towards solutions that are more likely a priori, typically those with small, smooth, or sparse coefficients. Here we introduce a novel Bayesian receptive field estimator designed to incorporate locality, a powerful form of prior information about receptive field structure. The key to our approach is a hierarchical receptive field model that flexibly adapts to localized structure in both spacetime and spatiotemporal frequency, using an inference method known as empirical Bayes. We refer to our method as automatic locality determination (ALD), and show that it can accurately recover various types of smooth, sparse, and localized receptive fields. We apply ALD to neural data from retinal ganglion cells and V1 simple cells, and find it achieves error rates several times lower than standard estimators. Thus, estimates of comparable accuracy can be achieved with substantially less data. Finally, we introduce a computationally efficient Markov Chain Monte Carlo (MCMC) algorithm for fully Bayesian inference under the ALD prior, yielding accurate Bayesian confidence intervals for small or noisy datasets. PMID:22046110

  8. Chronic neural probe for simultaneous recording of single-unit, multi-unit, and local field potential activity from multiple brain sites

    NASA Astrophysics Data System (ADS)

    Pothof, F.; Bonini, L.; Lanzilotto, M.; Livi, A.; Fogassi, L.; Orban, G. A.; Paul, O.; Ruther, P.

    2016-08-01

    Objective. Drug resistant focal epilepsy can be treated by resecting the epileptic focus requiring a precise focus localisation using stereoelectroencephalography (SEEG) probes. As commercial SEEG probes offer only a limited spatial resolution, probes of higher channel count and design freedom enabling the incorporation of macro and microelectrodes would help increasing spatial resolution and thus open new perspectives for investigating mechanisms underlying focal epilepsy and its treatment. This work describes a new fabrication process for SEEG probes with materials and dimensions similar to clinical probes enabling recording single neuron activity at high spatial resolution. Approach. Polyimide is used as a biocompatible flexible substrate into which platinum electrodes and leads are integrated with a minimal feature size of 5 μm. The polyimide foils are rolled into the cylindrical probe shape at a diameter of 0.8 mm. The resulting probe features match those of clinically approved devices. Tests in saline solution confirmed the probe stability and functionality. Probes were implanted into the brain of one monkey (Macaca mulatta), trained to perform different motor tasks. Suitable configurations including up to 128 electrode sites allow the recording of task-related neuronal signals. Main results. Probes with 32 and 64 electrode sites were implanted in the posterior parietal cortex. Local field potentials and multi-unit activity were recorded as early as one hour after implantation. Stable single-unit activity was achieved for up to 26 days after implantation of a 64-channel probe. All recorded signals showed modulation during task execution. Significance. With the novel probes it is possible to record stable biologically relevant data over a time span exceeding the usual time needed for epileptic focus localisation in human patients. This is the first time that single units are recorded along cylindrical polyimide probes chronically implanted 22 mm deep into the

  9. Decoding stimulus identity from multi-unit activity and local field potentials along the ventral auditory stream in the awake primate: implications for cortical neural prostheses

    NASA Astrophysics Data System (ADS)

    Smith, Elliot; Kellis, Spencer; House, Paul; Greger, Bradley

    2013-02-01

    Objective. Hierarchical processing of auditory sensory information is believed to occur in two streams: a ventral stream responsible for stimulus identity and a dorsal stream responsible for processing spatial elements of a stimulus. The objective of the current study is to examine neural coding in this processing stream in the context of understanding the possibility for an auditory cortical neural prosthesis. Approach. We examined the selectivity for species-specific primate vocalizations in the ventral auditory processing stream by applying a statistical classifier to neural data recorded from microelectrode arrays. Multi-unit activity (MUA) and local field potential (LFP) data recorded simultaneously from primary auditory complex (AI) and rostral parabelt (PBr) were decoded on a trial-by-trial basis. Main results. While decode performance in AI was well above chance, mean performance in PBr did not deviate >15% from chance level. Mean performance levels were similar for MUA and LFP decodes. Increasing the spectral and temporal resolution improved decode performance; while inter-electrode spacing could be as large as 1.14 mm without degrading decode performance. Significance. These results serve as preliminary guidance for a human auditory cortical neural prosthesis; instructing interface implementation, microstimulation patterns and anatomical placement.

  10. Relationships among low-frequency local field potentials, spiking activity, and three-dimensional reach and grasp kinematics in primary motor and ventral premotor cortices

    PubMed Central

    Vargas-Irwin, Carlos E.; Truccolo, Wilson; Donoghue, John P.

    2011-01-01

    A prominent feature of motor cortex field potentials during movement is a distinctive low-frequency local field potential (lf-LFP) (<4 Hz), referred to as the movement event-related potential (mEP). The lf-LFP appears to be a global signal related to regional synaptic input, but its relationship to nearby output signaled by single unit spiking activity (SUA) or to movement remains to be established. Previous studies comparing information in primary motor cortex (MI) lf-LFPs and SUA in the context of planar reaching tasks concluded that lf-LFPs have more information than spikes about movement. However, the relative performance of these signals was based on a small number of simultaneously recorded channels and units, or for data averaged across sessions, which could miss information of larger-scale spiking populations. Here, we simultaneously recorded LFPs and SUA from two 96-microelectrode arrays implanted in two major motor cortical areas, MI and ventral premotor (PMv), while monkeys freely reached for and grasped objects swinging in front of them. We compared arm end point and grip aperture kinematics′ decoding accuracy for lf-LFP and SUA ensembles. The results show that lf-LFPs provide enough information to reconstruct kinematics in both areas with little difference in decoding performance between MI and PMv. Individual lf-LFP channels often provided more accurate decoding of single kinematic variables than any one single unit. However, the decoding performance of the best single unit among the large population usually exceeded that of the best single lf-LFP channel. Furthermore, ensembles of SUA outperformed the pool of lf-LFP channels, in disagreement with the previously reported superiority of lf-LFP decoding. Decoding results suggest that information in lf-LFPs recorded from intracortical arrays may allow the reconstruction of reach and grasp for real-time neuroprosthetic applications, thus potentially supplementing the ability to decode these same

  11. Gauge field localization on brane worlds

    SciTech Connect

    Guerrero, Rommel; Rodriguez, R. Omar; Melfo, Alejandra; Pantoja, Nelson

    2010-04-15

    We consider the effects of spacetime curvature and brane thickness on the localization of gauge fields on a brane via kinetic terms induced by localized fermions. We find that in a warped geometry with an infinitely thin brane, both the infrared and the ultraviolet behavior of the electromagnetic propagator are affected, providing a more stringent bound on the brane's tension than that coming from the requirement of four-dimensional gravity on the brane. On the other hand, for a thick wall in a flat spacetime, where the fermions are localized by means of a Yukawa coupling, we find that four-dimensional electromagnetism is recovered in a region bounded from above by the same critical distance appearing in the thin case, but also from below by a new scale related to the brane's thickness and the electromagnetic couplings. This imposes very stringent bounds on the brane's thickness which seem to invalidate the localization mechanism for this case.

  12. Developing Photo Activated Localization Microscopy

    NASA Astrophysics Data System (ADS)

    Hess, Harald

    2015-03-01

    Photo Activated Localization Microscopy, PALM, acquires super-resolution images by activating a subset of activatable fluorescent labels and estimating the center of the each molecular label to sub-diffractive accuracy. When this process is repeated thousands of times for different subsets of molecules, then an image can be rendered from all the center coordinates of the molecules. I will describe the circuitous story of its development that began with another super-resolution technique, NSOM, developed by my colleague Eric Betzig, who imaged single molecules at room temperature, and later we spectrally resolved individual luminescent centers of quantum wells. These two observations inspired a generalized path to localization microscopy, but that path was abandoned because no really useful fluorescent labels were available. After a decade of nonacademic industrial pursuits and the subsequent freedom of unemployment, we came across a class of genetically expressible fluorescent proteins that were switchable or convertible that enabled the concept to be implemented and be biologically promising. The past ten years have been very active with many groups exploring applications and enhancements of this concept. Demonstrating significant biological relevance will be the metric if its success.

  13. Magnetic fields in Local Group dwarf irregulars

    NASA Astrophysics Data System (ADS)

    Chyży, K. T.; Weżgowiec, M.; Beck, R.; Bomans, D. J.

    2011-05-01

    Aims: We wish to clarify whether strong magnetic fields can be effectively generated in typically low-mass dwarf galaxies and to assess the role of dwarf galaxies in the magnetization of the Universe. Methods: We performed a search for radio emission and magnetic fields in an unbiased sample of 12 Local Group (LG) irregular and dwarf irregular galaxies with the 100-m Effelsberg telescope at 2.64 GHz. Three galaxies were detected. A higher frequency (4.85 GHz) was used to search for polarized emission in five dwarfs that are the most luminous ones in the infrared domain, of which three were detected. Results: Magnetic fields in LG dwarfs are weak, with a mean value of the total field strength of <4.2 ± 1.8 μG, three times lower than in the normal spirals. The strongest field among all LG dwarfs of 10 μG (at 2.64 GHz) is observed in the starburst dwarf IC 10. The production of total magnetic fields in dwarf systems appears to be regulated mainly by the star-formation surface density (with the power-law exponent of 0.30 ± 0.04) or by the gas surface density (with the exponent 0.47 ± 0.09). In addition, we find systematically stronger fields in objects of higher global star-formation rate. The dwarf galaxies follow a similar far-infrared relationship (with a slope of 0.91 ± 0.08) to that determined for high surface brightness spiral galaxies. The magnetic field strength in dwarf galaxies does not correlate with their maximum rotational velocity, indicating that a small-scale rather than a large-scale dynamo process is responsible for producting magnetic fields in dwarfs. If magnetization of the Universe by galactic outflows is coeval with its metal enrichment, we show that more massive objects (such as Lyman break galaxies) can efficiently magnetize the intergalactic medium with a magnetic field strength of about 0.8 nG out to a distance of 160-530 kpc at redshifts 5-3, respectively. Magnetic fields that are several times weaker and shorter magnetization

  14. Active localization of virtual sounds

    NASA Astrophysics Data System (ADS)

    Loomis, Jack M.; Hebert, C.; Cicinelli, J. G.

    1991-06-01

    We describe a virtual sound display built around a 12 MHz 80286 microcomputer and special purpose analog hardware. The display implements most of the primary cues for sound localization in the ear-level plane. Static information about direction is conveyed by interaural time differences and, for frequencies above 1800 Hz, by head sound shadow (interaural intensity differences) and pinna sound shadow. Static information about distance is conveyed by variation in sound pressure (first power law) for all frequencies, by additional attenuation in the higher frequencies (simulating atmospheric absorption), and by the proportion of direct to reverberant sound. When the user actively locomotes, the changing angular position of the source occasioned by head rotations provides further information about direction and the changing angular velocity produced by head translations (motion parallax) provides further information about distance. Judging both from informal observations by users and from objective data obtained in an experiment on homing to virtual and real sounds, we conclude that simple displays such as this are effective in creating the perception of external sounds to which subjects can home with accuracy and ease.

  15. Active localization of virtual sounds

    NASA Technical Reports Server (NTRS)

    Loomis, Jack M.; Hebert, C.; Cicinelli, J. G.

    1991-01-01

    We describe a virtual sound display built around a 12 MHz 80286 microcomputer and special purpose analog hardware. The display implements most of the primary cues for sound localization in the ear-level plane. Static information about direction is conveyed by interaural time differences and, for frequencies above 1800 Hz, by head sound shadow (interaural intensity differences) and pinna sound shadow. Static information about distance is conveyed by variation in sound pressure (first power law) for all frequencies, by additional attenuation in the higher frequencies (simulating atmospheric absorption), and by the proportion of direct to reverberant sound. When the user actively locomotes, the changing angular position of the source occasioned by head rotations provides further information about direction and the changing angular velocity produced by head translations (motion parallax) provides further information about distance. Judging both from informal observations by users and from objective data obtained in an experiment on homing to virtual and real sounds, we conclude that simple displays such as this are effective in creating the perception of external sounds to which subjects can home with accuracy and ease.

  16. Localization of disordered bosons and magnets in random fields

    SciTech Connect

    Yu, Xiaoquan; Müller, Markus

    2013-10-15

    We study localization properties of disordered bosons and spins in random fields at zero temperature. We focus on two representatives of different symmetry classes, hard-core bosons (XY magnets) and Ising magnets in random transverse fields, and contrast their physical properties. We describe localization properties using a locator expansion on general lattices. For 1d Ising chains, we find non-analytic behavior of the localization length as a function of energy at ω=0, ξ{sup −1}(ω)=ξ{sup −1}(0)+A|ω|{sup α}, with α vanishing at criticality. This contrasts with the much smoother behavior predicted for XY magnets. We use these results to approach the ordering transition on Bethe lattices of large connectivity K, which mimic the limit of high dimensionality. In both models, in the paramagnetic phase with uniform disorder, the localization length is found to have a local maximum at ω=0. For the Ising model, we find activated scaling at the phase transition, in agreement with infinite randomness studies. In the Ising model long range order is found to arise due to a delocalization and condensation initiated at ω=0, without a closing mobility gap. We find that Ising systems establish order on much sparser (fractal) subgraphs than XY models. Possible implications of these results for finite-dimensional systems are discussed. -- Highlights: •Study of localization properties of disordered bosons and spins in random fields. •Comparison between XY magnets (hard-core bosons) and Ising magnets. •Analysis of the nature of the magnetic transition in strong quenched disorder. •Ising magnets: activated scaling, no closing mobility gap at the transition. •Ising order emerges on sparser (fractal) support than XY order.

  17. Measuring Earth's Local Magnetic Field Using a Helmholtz Coil

    NASA Astrophysics Data System (ADS)

    Williams, Jonathan E.

    2014-04-01

    In this paper, I present a low-cost interactive experiment for measuring the strength of Earth's local magnetic field. This activity can be done in most high schools or two-year physics laboratories with limited resources, yet will have a tremendous learning impact. This experiment solidifies the three-dimensional nature of Earth's magnetic field vector and helps reinforce the aspect of the vertical component of Earth's magnetic field. Students should realize that Earth's magnetic field is not fully horizontal (except at the magnetic equator) and that a compass simply indicates the direction of the horizontal component of Earth's magnetic field. A magnetic dip needle compass can be used to determine the angle (known as the "dip angle" or "inclination angle") measured from the direction in which Earth's magnetic field vector points to the horizontal. In this activity, students will be able to determine the horizontal component of the field using a Helmholtz coil and, knowing the dip angle, the Earth's magnetic field strength can be determined.

  18. Localization of Free Field Realizations of Affine Lie Algebras

    NASA Astrophysics Data System (ADS)

    Futorny, Vyacheslav; Grantcharov, Dimitar; Martins, Renato A.

    2015-04-01

    We use localization technique to construct new families of irreducible modules of affine Kac-Moody algebras. In particular, localization is applied to the first free field realization of the affine Lie algebra or, equivalently, to imaginary Verma modules.

  19. From neurons to circuits: linear estimation of local field potentials.

    PubMed

    Rasch, Malte; Logothetis, Nikos K; Kreiman, Gabriel

    2009-11-01

    Extracellular physiological recordings are typically separated into two frequency bands: local field potentials (LFPs) (a circuit property) and spiking multiunit activity (MUA). Recently, there has been increased interest in LFPs because of their correlation with functional magnetic resonance imaging blood oxygenation level-dependent measurements and the possibility of studying local processing and neuronal synchrony. To further understand the biophysical origin of LFPs, we asked whether it is possible to estimate their time course based on the spiking activity from the same electrode or nearby electrodes. We used "signal estimation theory" to show that a linear filter operation on the activity of one or a few neurons can explain a significant fraction of the LFP time course in the macaque monkey primary visual cortex. The linear filter used to estimate the LFPs had a stereotypical shape characterized by a sharp downstroke at negative time lags and a slower positive upstroke for positive time lags. The filter was similar across different neocortical regions and behavioral conditions, including spontaneous activity and visual stimulation. The estimations had a spatial resolution of approximately 1 mm and a temporal resolution of approximately 200 ms. By considering a causal filter, we observed a temporal asymmetry such that the positive time lags in the filter contributed more to the LFP estimation than the negative time lags. Additionally, we showed that spikes occurring within approximately 10 ms of spikes from nearby neurons yielded better estimation accuracies than nonsynchronous spikes. In summary, our results suggest that at least some circuit-level local properties of the field potentials can be predicted from the activity of one or a few neurons. PMID:19889990

  20. Acquiring local field potential information from amperometric neurochemical recordings

    PubMed Central

    Zhang, Hao; Lin, Shih-Chieh; Nicolelis, Miguel A.L.

    2009-01-01

    Simultaneous acquisition of in vivo electrophysiological and neurochemical information is essential for understanding how endogenous neurochemicals modulate the dynamics of brain activity. However, up to now such a task has rarely been accomplished due to the major technical challenge of operating two independent recording systems simultaneously in real-time. Here we propose a simpler solution for achieving this goal by using only a standard electrochemical technique - amperometry. To demonstrate its feasibility, we compared amperometric signals with simultaneously recorded local field potential (LFP) signals. We found that the high frequency component (HFC) of the amperometric signals did not reflect neurochemical fluctuations, but instead it resembled LFPs in several aspects, including: (1) coherent spectral fluctuations; (2) clear characterization of different brain states; (3) identical hippocampal theta depth profile. As such, our findings provide the first demonstration that both LFP and local neurochemical information can be simultaneously acquired from electrochemical sensors alone. PMID:19428527

  1. The orientation of the local interstellar magnetic field.

    PubMed

    Opher, M; Stone, E C; Gombosi, T I

    2007-05-11

    The orientation of the local interstellar magnetic field introduces asymmetries in the heliosphere that affect the location of heliospheric radio emissions and the streaming direction of ions from the termination shock of the solar wind. We combined observations of radio emissions and energetic particle streaming with extensive three-dimensional magnetohydrodynamic computer simulations of magnetic field draping over the heliopause to show that the plane of the local interstellar field is approximately 60 degrees to 90 degrees from the galactic plane. This finding suggests that the field orientation in the Local Interstellar Cloud differs from that of a larger-scale interstellar magnetic field thought to parallel the galactic plane. PMID:17495167

  2. Phosphate vibrations probe local electric fields and hydration in biomolecules

    PubMed Central

    Levinson, Nicholas M.; Bolte, Erin E.; Miller, Carrie S.

    2011-01-01

    The role of electric fields in important biological processes like binding and catalysis has been studied almost exclusively by computational methods. Experimental measurements of the local electric field in macromolecules are possible using suitably calibrated vibrational probes. Here we demonstrate that the vibrational transitions of phosphate groups are highly sensitive to an electric field and quantify that sensitivity, allowing local electric field measurements to be made in phosphate-containing biological systems without chemical modification. PMID:21809829

  3. Local Magnetic Field Role in Star Formation

    NASA Astrophysics Data System (ADS)

    Koch, P. M.; Tang, Y. W.; Ho, P. T. P.; Zhang, Q.; Girart, J. M.; Chen, H. R. V.; Lai, S. P.; Li, H. B.; Li, Z. Y.; Liu, H. B.; Padovani, M.; Qiu, K.; Rao, R.; Yen, H. W.; Frau, P.; Chen, H. H.; Ching, T. C.

    2016-05-01

    We highlight distinct and systematic observational features of magnetic field morphologies in polarized submm dust continuum. We illustrate this with specific examples and show statistical trends from a sample of 50 star-forming regions.

  4. Localizing Region-Based Active Contours

    PubMed Central

    Lankton, Shawn; Tannenbaum, Allen

    2009-01-01

    In this paper, we propose a natural framework that allows any region-based segmentation energy to be re-formulated in a local way. We consider local rather than global image statistics and evolve a contour based on local information. Localized contours are capable of segmenting objects with heterogeneous feature profiles that would be difficult to capture correctly using a standard global method. The presented technique is versatile enough to be used with any global region-based active contour energy and instill in it the benefits of localization. We describe this framework and demonstrate the localization of three well-known energies in order to illustrate how our framework can be applied to any energy. We then compare each localized energy to its global counterpart to show the improvements that can be achieved. Next, an in-depth study of the behaviors of these energies in response to the degree of localization is given. Finally, we show results on challenging images to illustrate the robust and accurate segmentations that are possible with this new class of active contour models. PMID:18854247

  5. Spatially Distributed Local Fields in the Hippocampus Encode Rat Position

    PubMed Central

    Agarwal, Gautam; Stevenson, Ian H.; Berényi, Antal; Mizuseki, Kenji; Buzsáki, György; Sommer, Friedrich T.

    2016-01-01

    Although neuronal spikes can be readily detected from extracellular recordings, synaptic and subthreshold activity remains undifferentiated within the local field potential (LFP). In the hippocampus, neurons discharge selectively when the rat is at certain locations, while LFPs at single anatomical sites exhibit no such place-tuning. Nonetheless, because the representation of position is sparse and distributed, we hypothesized that spatial information can be recovered from multiple-site LFP recordings. Using high-density sampling of LFP and computational methods, we show that the spatiotemporal structure of the theta rhythm can encode position as robustly as neuronal spiking populations. Because our approach exploits the rhythmicity and sparse structure of neural activity, features found in many brain regions, it is useful as a general tool for discovering distributed LFP codes. PMID:24812401

  6. Local field potentials reflect multiple spatial scales in V4

    PubMed Central

    Mineault, Patrick J.; Zanos, Theodoros P.; Pack, Christopher C.

    2013-01-01

    Local field potentials (LFP) reflect the properties of neuronal circuits or columns recorded in a volume around a microelectrode (Buzsáki et al., 2012). The extent of this integration volume has been a subject of some debate, with estimates ranging from a few hundred microns (Katzner et al., 2009; Xing et al., 2009) to several millimeters (Kreiman et al., 2006). We estimated receptive fields (RFs) of multi-unit activity (MUA) and LFPs at an intermediate level of visual processing, in area V4 of two macaques. The spatial structure of LFP receptive fields varied greatly as a function of time lag following stimulus onset, with the retinotopy of LFPs matching that of MUAs at a restricted set of time lags. A model-based analysis of the LFPs allowed us to recover two distinct stimulus-triggered components: an MUA-like retinotopic component that originated in a small volume around the microelectrodes (~350 μm), and a second component that was shared across the entire V4 region; this second component had tuning properties unrelated to those of the MUAs. Our results suggest that the LFP reflects neural activity across multiple spatial scales, which both complicates its interpretation and offers new opportunities for investigating the large-scale structure of network processing. PMID:23533106

  7. Localized plasmonic field enhancement in shaped graphene nanoribbons.

    PubMed

    Xia, Sheng-Xuan; Zhai, Xiang; Wang, Ling-Ling; Lin, Qi; Wen, Shuang-Chun

    2016-07-25

    Graphene nanoribbon (GNR), as a fundamental component to support the surface plasmon waves, are envisioned to play an important role in graphene plasmonics. However, to achieve extremely confinement of the graphene surface plasmons (GSPs) is still a challenging. Here, we propose a scheme to realize the excitation of localized surface plasmons with very strong field enhancement at the resonant frequency. By sinusoidally patterning the boundaries of GNRs, a new type of plasmon mode with field energy concentrated on the shaped grating crest (crest mode) can be efficiently excited, creating a sharp notch on the transmission spectra. Specifically, the enhanced field energies are featured by 3 times of magnitude stronger than that of the unpatterned classical GNRs. Through theoretical analyses and numerical calculations, we confirm that the enhanced fields of the crest modes can be tuned not only by changing the width, period and Fermi energy as traditional ribbons, but also by varying the grating amplitude and period. This new technique of manipulating the light-graphene interaction gives an insight of modulating plasmon resonances on graphene nanostrutures, making the proposed pattern method an attractive candidate for designing optical filters, spatial light modulators, and other active plasmonic devices. PMID:27464087

  8. From Object Fields to Local Variables: A Practical Approach to Field-Sensitive Analysis

    NASA Astrophysics Data System (ADS)

    Albert, Elvira; Arenas, Puri; Genaim, Samir; Puebla, German; Ramírez Deantes, Diana Vanessa

    Static analysis which takes into account the value of data stored in the heap is typically considered complex and computationally intractable in practice. Thus, most static analyzers do not keep track of object fields (or fields for short), i.e., they are field-insensitive. In this paper, we propose locality conditions for soundly converting fields into local variables. This way, field-insensitive analysis over the transformed program can infer information on the original fields. Our notion of locality is context-sensitive and can be applied both to numeric and reference fields. We propose then a polyvariant transformation which actually converts object fields meeting the locality condition into variables and which is able to generate multiple versions of code when this leads to increasing the amount of fields which satisfy the locality conditions. We have implemented our analysis within a termination analyzer for Java bytecode.

  9. Optical probe, local fields, and Lorentz factor in ferroelectrics

    NASA Astrophysics Data System (ADS)

    Blinov, L. M.; Lazarev, V. V.; Palto, S. P.; Yudin, S. G.

    2014-06-01

    An optical probe is suggested that allows measurements of the local field and Lorentz factor ( L) in ferroelectric medium. The copolymer poly (vinylidene fluoride/trifluoroethylene) is mixed with Pd-tetraphenylporphyrin (TPP-Pd) that has a very narrow absorption band. Thus, TPP-Pd serves as a molecular optical probe of the local field. During the switching of the electric field lower than the coercive one the factor L of an unpolarized ferroelectric mixture is found to be of about 1/3 that corresponds to the random distribution of molecular dipoles in the ferroelectric. With increasing field, the dipole orientation acquires a lower symmetry and L tends to zero as predicted by lattice sum calculations for vinylidene fluoride. The knowledge of the field dependence of L and the usage of the optical probe makes it possible to measure directly the local and macroscopic fields in the individual elements of various ferroelectric-dielectric heterostructures.

  10. Acoustic source localization in mixed field using spherical microphone arrays

    NASA Astrophysics Data System (ADS)

    Huang, Qinghua; Wang, Tong

    2014-12-01

    Spherical microphone arrays have been used for source localization in three-dimensional space recently. In this paper, a two-stage algorithm is developed to localize mixed far-field and near-field acoustic sources in free-field environment. In the first stage, an array signal model is constructed in the spherical harmonics domain. The recurrent relation of spherical harmonics is independent of far-field and near-field mode strengths. Therefore, it is used to develop spherical estimating signal parameter via rotational invariance technique (ESPRIT)-like approach to estimate directions of arrival (DOAs) for both far-field and near-field sources. In the second stage, based on the estimated DOAs, simple one-dimensional MUSIC spectrum is exploited to distinguish far-field and near-field sources and estimate the ranges of near-field sources. The proposed algorithm can avoid multidimensional search and parameter pairing. Simulation results demonstrate the good performance for localizing far-field sources, or near-field ones, or mixed field sources.

  11. Subthalamic nucleus local field potential activity during the Eriksen flanker task reveals a novel role for theta phase during conflict monitoring.

    PubMed

    Zavala, Baltazar; Brittain, John-Stuart; Jenkinson, Ned; Ashkan, Keyoumars; Foltynie, Thomas; Limousin, Patricia; Zrinzo, Ludvic; Green, Alexander L; Aziz, Tipu; Zaghloul, Kareem; Brown, Peter

    2013-09-11

    The subthalamic nucleus (STN) is thought to play a central role in modulating responses during conflict. Computational models have suggested that the location of the STN in the basal ganglia, as well as its numerous connections to conflict-related cortical structures, allows it to be ideally situated to act as a global inhibitor during conflict. Additionally, recent behavioral experiments have shown that deep brain stimulation to the STN results in impulsivity during high-conflict situations. However, the precise mechanisms that mediate the "hold-your-horses" function of the STN remain unclear. We recorded from deep brain stimulation electrodes implanted bilaterally in the STN of 13 human subjects with Parkinson's disease while they performed a flanker task. The incongruent trials with the shortest reaction times showed no behavioral or electrophysiological differences from congruent trials, suggesting that the distracter stimuli were successfully ignored. In these trials, cue-locked STN theta band activity demonstrated phase alignment across trials and was followed by a periresponse increase in theta power. In contrast, incongruent trials with longer reaction times demonstrated a relative reduction in theta phase alignment followed by higher theta power. Theta phase alignment negatively correlated with subject reaction time, and theta power positively correlated with trial reaction time. Thus, when conflicting stimuli are not properly ignored, disruption of STN theta phase alignment may help operationalize the hold-your-horses role of the nucleus, whereas later increases in the amplitude of theta oscillations may help overcome this function. PMID:24027276

  12. Plasmon localization and local field distribution in metal-dielectric films.

    PubMed

    Genov, Dentcho A; Sarychev, Andrey K; Shalaev, Vladimir M

    2003-05-01

    An exact and very efficient numerical method for calculating the effective conductivity and local-field distributions in random R-L-C networks is developed. Using this method, the local-field properties of random metal-dielectric films are investigated in a wide spectral range and for a variety of metal concentrations p. It is shown that for metal concentrations close to the percolation threshold (p=p(c)) and frequencies close to the resonance, the local-field intensity is characterized by a non-Gaussian, exponentially broad distribution. For low and high metal concentrations a scaling region is formed that is due to the increasing number of noninteracting dipoles. The local electric fields are studied in terms of characteristic length parameters. The roles of both localized and extended eigenmodes in Kirchhoff's Hamiltonian are investigated. PMID:12786300

  13. Localized spin wave modes in parabolic field wells

    NASA Astrophysics Data System (ADS)

    McMichael, Robert; Tartakovskaya, Elena; Pardavi-Horvath, Martha

    We describe spin wave modes trapped in parabolic-profile field wells. Trapped spin waves can be used as local probes of magnetic properties with resolution down to 100 nm in ferromagnetic resonance force microscopy. Localized modes have been shown to form around field minima from a number of sources, including stray fields from magnetic probe tips and inhomogeneous magnetostatic fields near film edges. Here, we address the most basic trap, which is a parabolic minimum in the applied field. The magnetic eigenmodes in this trap are tractable enough to serve as approximations in more realistic situations. For a parabolic field, we select basis mode profiles proportional to Hermite functions because they are eigenfuctions of the applied field and exchange parts of the equations of motion. Additionally, we find that these Hermite modes are approximate eigenfunctions of magnetostatic interactions, showing good agreement with micromagnetic calculations. More precise agreement is achieved by diagonalizing the equations of motion using only a few modes.

  14. Local Field Factors and Dielectric Properties of Liquid Benzene.

    PubMed

    Davari, Nazanin; Daub, Christopher D; Åstrand, Per-Olof; Unge, Mikael

    2015-09-01

    Local electric field factors are calculated for liquid benzene by combining molecular dynamic simulations with a subsequent force-field model based on a combined charge-transfer and point-dipole interaction model for the local field factor. The local field factor is obtained as a linear response of the local field to an external electric field, and the response is calculated at frequencies through the first absorption maximum. It is found that the largest static local field factor is around 2.4, while it is around 6.4 at the absorption frequency. The linear susceptibility, the dielectric constant, and the first absorption maximum of liquid benzene are also studied. The electronic contribution to the dielectric constant is around 2.3 at zero frequency, in good agreement with the experimental value around 2.2, while it increases to 6.3 at the absorption frequency. The π → π* excitation energy is around 6.0 eV, as compared to the gas-phase value of around 6.3 eV, while the experimental values are 6.5 and 6.9 eV for the liquid and gas phase, respectively, demonstrating that the gas-to-liquid shift is well-described. PMID:26241379

  15. Creating Local Field Trips: Seeing Geographical Principles through Empirical Eyes.

    ERIC Educational Resources Information Center

    Wheeler, James O.

    1985-01-01

    Discusses how instructors can design a local field trip for undergraduate students enrolled in an economic geography class. The purpose of the field trip is to help students observe and interpret familiar scenes in terms of geographical concepts such as central place theory, changing land use, and spatial competition. (RM)

  16. Anisotropies in magnetic field evolution and local Lyapunov exponents

    SciTech Connect

    Tang, X.Z.; Boozer, A.H.

    2000-01-13

    The natural occurrence of small scale structures and the extreme anisotropy in the evolution of a magnetic field embedded in a conducting flow is interpreted in terms of the properties of the local Lyapunov exponents along the various local characteristic (un)stable directions for the Lagrangian flow trajectories. The local Lyapunov exponents and the characteristic directions are functions of Lagrangian coordinates and time, which are completely determined once the flow field is specified. The characteristic directions that are associated with the spatial anisotropy of the problem, are prescribed in both Lagrangian and Eulerian frames. Coordinate transformation techniques are employed to relate the spatial distributions of the magnetic field, the induced current density, and the Lorentz force, which are usually followed in Eulerian frame, to those of the local Lyapunov exponents, which are naturally defined in Lagrangian coordinates.

  17. Magnetic-field-induced localization in 2D topological insulators.

    PubMed

    Delplace, Pierre; Li, Jian; Büttiker, Markus

    2012-12-14

    Localization of the helical edge states in quantum spin Hall insulators requires breaking time-reversal invariance. In experiments, this is naturally implemented by applying a weak magnetic field B. We propose a model based on scattering theory that describes the localization of helical edge states due to coupling to random magnetic fluxes. We find that the localization length is proportional to B^{-2} when B is small and saturates to a constant when B is sufficiently large. We estimate especially the localization length for the HgTe/CdTe quantum wells with known experimental parameters. PMID:23368362

  18. Local Flow Field and Slip Length of Superhydrophobic Surfaces.

    PubMed

    Schäffel, David; Koynov, Kaloian; Vollmer, Doris; Butt, Hans-Jürgen; Schönecker, Clarissa

    2016-04-01

    While the global slippage of water past superhydrophobic surfaces has attracted wide interest, the local distribution of slip still remains unclear. Using fluorescence correlation spectroscopy, we performed detailed measurements of the local flow field and slip length for water in the Cassie state on a microstructured superhydrophobic surface. We revealed that the local slip length is finite, nonconstant, anisotropic, and sensitive to the presence of surfactants. In combination with numerical calculations of the flow, we can explain all these properties by the local hydrodynamics. PMID:27081981

  19. Local Flow Field and Slip Length of Superhydrophobic Surfaces

    NASA Astrophysics Data System (ADS)

    Schäffel, David; Koynov, Kaloian; Vollmer, Doris; Butt, Hans-Jürgen; Schönecker, Clarissa

    2016-04-01

    While the global slippage of water past superhydrophobic surfaces has attracted wide interest, the local distribution of slip still remains unclear. Using fluorescence correlation spectroscopy, we performed detailed measurements of the local flow field and slip length for water in the Cassie state on a microstructured superhydrophobic surface. We revealed that the local slip length is finite, nonconstant, anisotropic, and sensitive to the presence of surfactants. In combination with numerical calculations of the flow, we can explain all these properties by the local hydrodynamics.

  20. Local and nonlocal parallel heat transport in general magnetic fields

    SciTech Connect

    Del-Castillo-Negrete, Diego B; Chacon, Luis

    2011-01-01

    A novel approach for the study of parallel transport in magnetized plasmas is presented. The method avoids numerical pollution issues of grid-based formulations and applies to integrable and chaotic magnetic fields with local or nonlocal parallel closures. In weakly chaotic fields, the method gives the fractal structure of the devil's staircase radial temperature profile. In fully chaotic fields, the temperature exhibits self-similar spatiotemporal evolution with a stretched-exponential scaling function for local closures and an algebraically decaying one for nonlocal closures. It is shown that, for both closures, the effective radial heat transport is incompatible with the quasilinear diffusion model.

  1. Localized electron heating by strong guide-field magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Guo, Xuehan; Inomoto, Michiaki; Sugawara, Takumichi; Yamasaki, Kotaro; Ushiki, Tomohiko; Ono, Yasushi

    2015-10-01

    Localized electron heating of magnetic reconnection was studied under strong guide-field using two merging spherical tokamak plasmas in the University of Tokyo Spherical Tokamak experiment. Our new slide-type two-dimensional Thomson scattering system is documented for the first time the electron heating localized around the X-point. Shape of the high electron temperature area does not agree with that of energy dissipation term Et.jt . If we include a guide-field effect term Bt/(Bp+αBt) for Et.jt , the energy dissipation area becomes localized around the X-point, suggesting that the electrons are accelerated by the reconnection electric field parallel to the magnetic field and thermalized around the X-point.

  2. Generalized conservation laws in non-local field theories

    NASA Astrophysics Data System (ADS)

    Kegeles, Alexander; Oriti, Daniele

    2016-04-01

    We propose a geometrical treatment of symmetries in non-local field theories, where the non-locality is due to a lack of identification of field arguments in the action. We show that the existence of a symmetry of the action leads to a generalized conservation law, in which the usual conserved current acquires an additional non-local correction term, obtaining a generalization of the standard Noether theorem. We illustrate the general formalism by discussing the specific physical example of complex scalar field theory of the type describing the hydrodynamic approximation of Bose-Einstein condensates. We expect our analysis and results to be of particular interest for the group field theory formulation of quantum gravity.

  3. Adjoint active surfaces for localization and imaging.

    PubMed

    Cook, Daniel A; Mueller, Martin Fritz; Fedele, Francesco; Yezzi, Anthony J

    2015-01-01

    This paper addresses the problem of localizing and segmenting regions embedded within a surrounding medium by characterizing their boundaries, as opposed to imaging the entirety of the volume. Active surfaces are used to directly reconstruct the shape of the region of interest. We describe the procedure for finding the optimal surface, which is computed iteratively via gradient descent that exploits the sensitivity of an error minimization functional to changes of the active surface. In doing so, we introduce the adjoint model to compute the sensitivity, and in this respect, the method shares common ground with several other disciplines, such as optimal control. Finally, we illustrate the proposed active surface technique in the framework of wave propagation governed by the scalar Helmholtz equation. Potential applications include electromagnetics, acoustics, geophysics, nondestructive testing, and medical imaging. PMID:25438311

  4. Thinking Globally, Planning Nationally and Acting Locally: Nested Organizational Fields and the Adoption of Environmental Practices

    ERIC Educational Resources Information Center

    Vasi, Ion Bogdan

    2007-01-01

    The study of the adoption of activities to protect the natural environment has tended to focus on the role of organizational fields. This article advances existing research by simultaneously examining conflicting processes that operate in nested organizational fields at local, national and supra-national levels. It examines the recent spread of an…

  5. Local-field correction in the strong-coupling regime

    SciTech Connect

    Hien, Tran Minh; Dung, Ho Trung; Welsch, Dirk-Gunnar

    2011-04-15

    The influence of the local-field correction on the strong atom-field coupling regime are investigated using the real-cavity model. The atom is positioned at the center of a multilayer sphere. Three types of mirrors are considered: perfectly reflecting, Lorentz band gap, and Bragg-distributed ones, with special emphasis on experimental practicability. In particular, the influence of the local field on the spectral resonance lines, the Rabi oscillation frequency and decay rate, and the condition indicating the occurrence of the strong-coupling regime are studied in detail. It is shown that the local-field correction gives rise to a structureless plateau in the density of states of the electromagnetic field. The level of the plateau rises with increasing material density and/or absorption, which may eventually destroy the strong-coupling regime. The effect of the local field is especially pronounced at high-material densities due to direct energy transfer from the guest atom to the medium. At lower material density and/or absorption, variation of the material density does not seem to affect much the strong-coupling regime, except for a small shift in the resonance frequency.

  6. Localized Dictionaries Based Orientation Field Estimation for Latent Fingerprints.

    PubMed

    Xiao Yang; Jianjiang Feng; Jie Zhou

    2014-05-01

    Dictionary based orientation field estimation approach has shown promising performance for latent fingerprints. In this paper, we seek to exploit stronger prior knowledge of fingerprints in order to further improve the performance. Realizing that ridge orientations at different locations of fingerprints have different characteristics, we propose a localized dictionaries-based orientation field estimation algorithm, in which noisy orientation patch at a location output by a local estimation approach is replaced by real orientation patch in the local dictionary at the same location. The precondition of applying localized dictionaries is that the pose of the latent fingerprint needs to be estimated. We propose a Hough transform-based fingerprint pose estimation algorithm, in which the predictions about fingerprint pose made by all orientation patches in the latent fingerprint are accumulated. Experimental results on challenging latent fingerprint datasets show the proposed method outperforms previous ones markedly. PMID:26353229

  7. Pedestrian simulations in hexagonal cell local field model

    NASA Astrophysics Data System (ADS)

    Leng, Biao; Wang, Jianyuan; Xiong, Zhang

    2015-11-01

    Pedestrian dynamics have caused wide concern over the recent years. This paper presents a local field (LF) model based on regular hexagonal cells to simulate pedestrian dynamics in scenarios such as corridors and bottlenecks. In this model, the simulation scenarios are discretized into regular hexagonal cells. The local field is a small region around pedestrian. Each pedestrian will choose his/her target cell according to the situation in his/her local field. Different walking strategies are considered in the simulation in corridor scenario and the fundamental graphs are used to verify this model. Different shapes of exit are also discussed in the bottleneck scenario. The statistics of push effect show that the smooth bottleneck exit may be more safe.

  8. Locally oriented potential field for controlling multi-robots

    NASA Astrophysics Data System (ADS)

    Romero, Roseli A. F.; Prestes, Edson; Idiart, Marco A. P.; Faria, Gedson

    2012-12-01

    In this paper, we present an extension of the boundary value problem path planner (BVP PP) to control multiple robots in a robot soccer scenario. This extension is called Locally Oriented Potential Field (LOPF) and computes a potential field from the numerical solution of a BVP using local relaxations in different patches of the solution space. This permits that a single solution of the BVP endows distinct robots with different behaviors in a team. We present the steps to implement LOPF as well as several results obtained in simulation.

  9. Localized Electron Heating by Strong Guide-Field Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Guo, Xuehan; Sugawara, Takumichi; Inomoto, Michiaki; Yamasaki, Kotaro; Ono, Yasushi; UTST Team

    2015-11-01

    Localized electron heating of magnetic reconnection was studied under strong guide-field (typically Bt 15Bp) using two merging spherical tokamak plasmas in Univ. Tokyo Spherical Tokamak (UTST) experiment. Our new slide-type two-dimensional Thomson scattering system documented for the first time the electron heating localized around the X-point. The region of high electron temperature, which is perpendicular to the magnetic field, was found to have a round shape with radius of 2 [cm]. Also, it was localized around the X-point and does not agree with that of energy dissipation term Et .jt . When we include a guide-field effect term Bt / (Bp + αBt) for Et .jt where α =√{ (vin2 +vout2) /v∥2 } , the energy dissipation area becomes localized around the X-point, suggesting that the electrons are accelerated by the reconnection electric field parallel to the magnetic field and thermalized around the X-point. This work was supported by JSPS A3 Foresight Program ``Innovative Tokamak Plasma Startup and Current Drive in Spherical Torus,'' a Grant-in-Aid from the Japan Society for the Promotion of Science (JSPS) Fellows 15J03758.

  10. Nonequilibrium electromagnetics: Local and macroscopic fields and constitutive relationships

    SciTech Connect

    Baker-Jarvis, James; Kabos, Pavel; Holloway, Christopher L.

    2004-09-01

    We study the electrodynamics of materials using a Liouville-Hamiltonian-based statistical-mechanical theory. Our goal is to develop electrodynamics from an ensemble-average viewpoint that is valid for microscopic and nonequilibrium systems at molecular to submolecular scales. This approach is not based on a Taylor series expansion of the charge density to obtain the multipoles. Instead, expressions of the molecular multipoles are used in an inverse problem to obtain the averaging statistical-density function that is used to obtain the macroscopic fields. The advantages of this method are that the averaging function is constructed in a self-consistent manner and the molecules can either be treated as point multipoles or contain more microstructure. Expressions for the local and macroscopic fields are obtained, and evolution equations for the constitutive parameters are developed. We derive equations for the local field as functions of the applied, polarization, magnetization, strain density, and macroscopic fields.

  11. Virtual local target method for avoiding local minimum in potential field based robot navigation.

    PubMed

    Zou, Xi-Yong; Zhu, Jing

    2003-01-01

    A novel robot navigation algorithm with global path generation capability is presented. Local minimum is a most intractable but is an encountered frequently problem in potential field based robot navigation. Through appointing appropriately some virtual local targets on the journey, it can be solved effectively. The key concept employed in this algorithm are the rules that govern when and how to appoint these virtual local targets. When the robot finds itself in danger of local minimum, a virtual local target is appointed to replace the global goal temporarily according to the rules. After the virtual target is reached, the robot continues on its journey by heading towards the global goal. The algorithm prevents the robot from running into local minima anymore. Simulation results showed that it is very effective in complex obstacle environments. PMID:12765277

  12. Visualizing electromagnetic fields at the nanoscale by single molecule localization.

    PubMed

    Steuwe, Christian; Erdelyi, Miklos; Szekeres, G; Csete, M; Baumberg, Jeremy J; Mahajan, Sumeet; Kaminski, Clemens F

    2015-05-13

    Coupling of light to the free electrons at metallic surfaces allows the confinement of electric fields to subwavelength dimensions, far below the optical diffraction limit. While this is routinely used to manipulate light at the nanoscale, in electro-optic devices and enhanced spectroscopic techniques, no characterization technique for imaging the underlying nanoscopic electromagnetic fields exists, which does not perturb the field or employ complex electron beam imaging. Here, we demonstrate the direct visualization of electromagnetic fields on patterned metallic substrates at nanometer resolution, exploiting a strong "autonomous" fluorescence-blinking behavior of single molecules within the confined fields allowing their localization. Use of DNA-constructs for precise positioning of fluorescence dyes on the surface induces this distance-dependent autonomous blinking thus completely obviating the need for exogenous agents or switching methods. Mapping such electromagnetic field distributions at nanometer resolution aids the rational design of nanometals for diverse photonic applications. PMID:25915093

  13. Suppression of edge-localized modes by magnetic field perturbations

    SciTech Connect

    Kleva, Robert G.; Guzdar, Parvez N.

    2010-11-15

    Transport bursts in simulations of edge-localized modes (ELMs) in tokamaks are suppressed by the application of magnetic field perturbations. The amplitude of the applied magnetic field perturbations is characterized by a stochasticity parameter S. When S>1, magnetic flux surfaces are destroyed and the magnetic field lines diffuse in minor radius. As S increases in the simulations, the magnitude of the ELM bursts decreases. The size of bursts is reduced to a very small value while S is still less than unity and most of the magnetic flux surfaces are still preserved. Magnetic field line stochasticity is not a requirement for the stabilization of ELMs by the magnetic field perturbations. The magnetic field perturbations act by suppressing the growth of the resistive ballooning instability that underlies the ELM bursts.

  14. Statistical Interpretation of the Local Field Inside Dielectrics.

    ERIC Educational Resources Information Center

    Berrera, Ruben G.; Mello, P. A.

    1982-01-01

    Compares several derivations of the Clausius-Mossotti relation to analyze consistently the nature of approximations used and their range of applicability. Also presents a statistical-mechanical calculation of the local field for classical system of harmonic oscillators interacting via the Coulomb potential. (Author/SK)

  15. Local Scalar Fields Equivalent to Nambu-Goto Strings

    NASA Astrophysics Data System (ADS)

    Hosotani, Yutaka

    1981-08-01

    We prove the mathematical equivalence of Nambu-Goto strings to local scalar fields S(x) and T (x) described by the Lagrangian L=-d4x{[∂(S,T)∂(xμ,xν)]22}12 Implications to the quantization problem of strings are also discussed.

  16. Harmonic analysis on local fields and adelic spaces. II

    NASA Astrophysics Data System (ADS)

    Osipov, Denis V.; Parshin, Aleksei N.

    2011-08-01

    We develop harmonic analysis in certain categories of filtered Abelian groups and vector spaces. The objects of these categories include local fields and adelic spaces arising from arithmetic surfaces. We prove some structure theorems for quotients of the adèle groups of algebraic and arithmetic surfaces.

  17. Gene flow in maize fields with different local pollen densities

    NASA Astrophysics Data System (ADS)

    Goggi, A. Susana; Lopez-Sanchez, Higinio; Caragea, Petrutza; Westgate, Mark; Arritt, Raymond; Clark, Craig A.

    2007-08-01

    The development of maize ( Zea mays L.) varieties as factories of pharmaceutical and industrial compounds has renewed interest in controlling pollen dispersal. The objective of this study was to compare gene flow into maize fields of different local pollen densities under the same environmental conditions. Two fields of approximately 36 ha were planted with a nontransgenic, white hybrid, in Ankeny, Iowa, USA. In the center of both fields, a 1-ha plot of a yellow-seeded stacked RR/Bt transgenic hybrid was planted as a pollen source. Before flowering, the white receiver maize of one field was detasseled in a 4:1 ratio to reduce the local pollen density (RPD). The percentage of outcross in the field with RPD was 42.2%, 6.3%, and 1.3% at 1, 10, and 35 m from the central plot, respectively. The percentage of outcross in the white maize with normal pollen density (NPD) was 30.1%, 2.7%, and 0.4%, respectively, at these distances. At distances greater than 100 m, the outcross frequency decreased below 0.1 and 0.03% in the field with RPD and NPD, respectively. A statistical model was used to compare pollen dispersal based on observed outcross percentages. The likelihood ratio test confirmed that the models of outcrossing in the two fields were significantly different ( P is practically 0). Results indicated that when local pollen is low, the incoming pollen has a competitive advantage and the level of outcross is significantly greater than when the local pollen is abundant.

  18. Locally smeared operator product expansions in scalar field theory

    SciTech Connect

    Monahan, Christopher; Orginos, Kostas

    2015-04-01

    We propose a new locally smeared operator product expansion to decompose non-local operators in terms of a basis of smeared operators. The smeared operator product expansion formally connects nonperturbative matrix elements determined numerically using lattice field theory to matrix elements of non-local operators in the continuum. These nonperturbative matrix elements do not suffer from power-divergent mixing on the lattice, which significantly complicates calculations of quantities such as the moments of parton distribution functions, provided the smearing scale is kept fixed in the continuum limit. The presence of this smearing scale complicates the connection to the Wilson coefficients of the standard operator product expansion and requires the construction of a suitable formalism. We demonstrate the feasibility of our approach with examples in real scalar field theory.

  19. Locally smeared operator product expansions in scalar field theory

    DOE PAGESBeta

    Monahan, Christopher; Orginos, Kostas

    2015-04-01

    We propose a new locally smeared operator product expansion to decompose non-local operators in terms of a basis of smeared operators. The smeared operator product expansion formally connects nonperturbative matrix elements determined numerically using lattice field theory to matrix elements of non-local operators in the continuum. These nonperturbative matrix elements do not suffer from power-divergent mixing on the lattice, which significantly complicates calculations of quantities such as the moments of parton distribution functions, provided the smearing scale is kept fixed in the continuum limit. The presence of this smearing scale complicates the connection to the Wilson coefficients of the standardmore » operator product expansion and requires the construction of a suitable formalism. We demonstrate the feasibility of our approach with examples in real scalar field theory.« less

  20. GROWTH OF A LOCALIZED SEED MAGNETIC FIELD IN A TURBULENT MEDIUM

    SciTech Connect

    Cho, Jungyeon; Yoo, Hyunju

    2012-11-10

    Turbulence dynamo deals with the amplification of a seed magnetic field in a turbulent medium and has been studied mostly for uniform or spatially homogeneous seed magnetic fields. However, some astrophysical processes (e.g., jets from active galaxies, galactic winds, or ram-pressure stripping in galaxy clusters) can provide localized seed magnetic fields. In this paper, we numerically study amplification of localized seed magnetic fields in a turbulent medium. Throughout the paper, we assume that the driving scale of turbulence is comparable to the size of the system. Our findings are as follows. First, turbulence can amplify a localized seed magnetic field very efficiently. The growth rate of magnetic energy density is as high as that for a uniform seed magnetic field. This result implies that magnetic field ejected from an astrophysical object can be a viable source of a magnetic field in a cluster. Second, the localized seed magnetic field disperses and fills the whole system very fast. If turbulence in a system (e.g., a galaxy cluster or a filament) is driven at large scales, we expect that it takes a few large-eddy turnover times for the magnetic field to fill the whole system. Third, growth and turbulence diffusion of a localized seed magnetic field are also fast in high magnetic Prandtl number turbulence. Fourth, even in decaying turbulence, a localized seed magnetic field can ultimately fill the whole system. Although the dispersal rate of the magnetic field is not fast in purely decaying turbulence, it can be enhanced by an additional forcing.

  1. Convective Flow Induced by Localized Traveling Magnetic Fields

    NASA Technical Reports Server (NTRS)

    Mazuruk, Konstantin; Rose, M. Franklin (Technical Monitor)

    2001-01-01

    An axisymmetric traveling magnetic field induces a meridional base flow in a cylindrical zone of an electrically conducting liquid. This remotely induced flow can be conveniently controlled, in magnitude and direction, and can have benefits for crystal growth applications. In particular, it can be used to offset natural convection. For long vertical cylinders, non-uniform and localized in the propagating direction, magnetic fields are required for this purpose. Here we investigate a particular form of this field, namely that induced by a set of a few electric current coils. An order of magnitude reduction of buoyancy convection is theoretically demonstrated for a vertical Bridgman crystal growth configuration.

  2. Dynamic-local-field approximation for the quantum solids

    NASA Technical Reports Server (NTRS)

    Etters, R. D.; Danilowicz, R. L.

    1974-01-01

    A local-molecular-field description for the ground-state properties of the quantum solids is presented. The dynamical behavior of atoms contributing to the local field, which acts on an arbitrary pair of test particles, is incorporated by decoupling the pair correlations between these field atoms. The energy, pressure, compressibility, single-particle-distribution function, and the rms atomic deviations about the equilibrium lattice sites are calculated for H2, He-3, and He-4 over the volume range from 5 to 24.5 cu cm/mole. The results are in close agreement with existing Monte Carlo calculations wherever comparisons are possible. At very high pressure, the results agree with simplified descriptions which depend on negligible overlap of the system wave function between neighboring lattice sites.

  3. Quantum entanglement of local operators in conformal field theories.

    PubMed

    Nozaki, Masahiro; Numasawa, Tokiro; Takayanagi, Tadashi

    2014-03-21

    We introduce a series of quantities which characterize a given local operator in any conformal field theory from the viewpoint of quantum entanglement. It is defined by the increased amount of (Rényi) entanglement entropy at late time for an excited state defined by acting the local operator on the vacuum. We consider a conformal field theory on an infinite space and take the subsystem in the definition of the entanglement entropy to be its half. We calculate these quantities for a free massless scalar field theory in two, four and six dimensions. We find that these results are interpreted in terms of quantum entanglement of a finite number of states, including Einstein-Podolsky-Rosen states. They agree with a heuristic picture of propagations of entangled particles. PMID:24702348

  4. Simplest relationship between local field potential and intracellular signals in layered neural tissue

    NASA Astrophysics Data System (ADS)

    Chizhov, Anton V.; Sanchez-Aguilera, Alberto; Rodrigues, Serafim; de la Prida, Liset Menendez

    2015-12-01

    The relationship between the extracellularly measured electric field potential resulting from synaptic activity in an ensemble of neurons and intracellular signals in these neurons is an important but still open question. Based on a model neuron with a cylindrical dendrite and lumped soma, we derive a formula that substantiates a proportionality between the local field potential and the total somatic transmembrane current that emerges from the difference between the somatic and dendritic membrane potentials. The formula is tested by intra- and extracellular recordings of evoked synaptic responses in hippocampal slices. Additionally, the contribution of different membrane currents to the field potential is demonstrated in a two-population mean-field model. Our formalism, which allows for a simple estimation of unknown dendritic currents directly from somatic measurements, provides an interpretation of the local field potential in terms of intracellularly measurable synaptic signals. It is also applicable to the study of cortical activity using two-compartment neuronal population models.

  5. Simplest relationship between local field potential and intracellular signals in layered neural tissue.

    PubMed

    Chizhov, Anton V; Sanchez-Aguilera, Alberto; Rodrigues, Serafim; de la Prida, Liset Menendez

    2015-12-01

    The relationship between the extracellularly measured electric field potential resulting from synaptic activity in an ensemble of neurons and intracellular signals in these neurons is an important but still open question. Based on a model neuron with a cylindrical dendrite and lumped soma, we derive a formula that substantiates a proportionality between the local field potential and the total somatic transmembrane current that emerges from the difference between the somatic and dendritic membrane potentials. The formula is tested by intra- and extracellular recordings of evoked synaptic responses in hippocampal slices. Additionally, the contribution of different membrane currents to the field potential is demonstrated in a two-population mean-field model. Our formalism, which allows for a simple estimation of unknown dendritic currents directly from somatic measurements, provides an interpretation of the local field potential in terms of intracellularly measurable synaptic signals. It is also applicable to the study of cortical activity using two-compartment neuronal population models. PMID:26764724

  6. Spectral investigation of nonlinear local field effects in Ag nanoparticles

    SciTech Connect

    Sato, Rodrigo Takeda, Yoshihiko; Ohnuma, Masato; Oyoshi, Keiji

    2015-03-21

    The capability of Ag nanoparticles to modulate their optical resonance condition, by optical nonlinearity, without an external feedback system was experimentally demonstrated. These optical nonlinearities were studied in the vicinity of the localized surface plasmon resonance (LSPR), using femtosecond pump-and-probe spectroscopy with a white-light continuum probe. Transient transmission changes ΔT/T exhibited strong photon energy and particle size dependence and showed a complex and non-monotonic change with increasing pump light intensity. Peak position and change of sign redshift with increasing pump light intensity demonstrate the modulation of the LSPR. These features are discussed in terms of the intrinsic feedback via local field enhancement.

  7. Local capacitor model for plasmonic electric field enhancement.

    PubMed

    Kang, J H; Kim, D S; Park, Q-Han

    2009-03-01

    We present a local capacitor model that enables a simple yet quantitatively accurate description of lightning rod effect in nanoplasmonics. A notion of lambda-zone capacitance is proposed and applied to predict the strongly induced electric field by a light source near nanoscale metal edges such as metal tip or metal gap. The enhancement factor, calculated from the local capacitor model, shows excellent agreement with more rigorous results. The lambda-zone capacitor allows a blockwise treatment of nano-optical devices and constitutes a basic element of optical nanocircuits. PMID:19392523

  8. Orientation correlation and local field in liquid nitrobenzene

    NASA Astrophysics Data System (ADS)

    Shelton, David P.

    2016-06-01

    Hyper-Rayleigh scattering (HRS) is sensitive to long-range molecular orientation correlation in isotropic liquids composed of dipolar molecules. Measurements of the polarization, angle, and spectral dependence for HRS from liquid nitrobenzene (NB) are analyzed to determine the NB molecular orientation correlations at long range. The longitudinal and transverse orientation correlation functions for r > 3 nm are BL(r) = (a/r)3 and BT(r) = - BL(r)/2, where a = 0.20 ± 0.01 nm. Measurements of HRS induced by dissolved ions are also analyzed and combined with molecular dynamics simulation and dielectric response results, to determine the molecular dipole moment μ = 3.90 ± 0.04 D, Kirkwood orientation correlation factor gK = 0.68 ± 0.02, and local field factor f(0) = 0.85 ± 0.04 × Onsager local field factor in liquid nitrobenzene.

  9. Orientation correlation and local field in liquid nitrobenzene.

    PubMed

    Shelton, David P

    2016-06-21

    Hyper-Rayleigh scattering (HRS) is sensitive to long-range molecular orientation correlation in isotropic liquids composed of dipolar molecules. Measurements of the polarization, angle, and spectral dependence for HRS from liquid nitrobenzene (NB) are analyzed to determine the NB molecular orientation correlations at long range. The longitudinal and transverse orientation correlation functions for r > 3 nm are BL(r) = (a/r)(3) and BT(r) = - BL(r)/2, where a = 0.20 ± 0.01 nm. Measurements of HRS induced by dissolved ions are also analyzed and combined with molecular dynamics simulation and dielectric response results, to determine the molecular dipole moment μ = 3.90 ± 0.04 D, Kirkwood orientation correlation factor gK = 0.68 ± 0.02, and local field factor f(0) = 0.85 ± 0.04 × Onsager local field factor in liquid nitrobenzene. PMID:27334178

  10. The local dayside reconnection rate for oblique interplanetary magnetic fields

    NASA Astrophysics Data System (ADS)

    Komar, C. M.; Cassak, P. A.

    2016-06-01

    We present an analysis of local properties of magnetic reconnection at the dayside magnetopause for various interplanetary magnetic field (IMF) orientations in global magnetospheric simulations. This has heretofore not been practical because it is difficult to locate where reconnection occurs for oblique IMF, but new techniques make this possible. The approach is to identify magnetic separators, the curves separating four regions of differing magnetic topology, which map the reconnection X line. The electric field parallel to the X line is the local reconnection rate. We compare results to a simple model of local two-dimensional asymmetric reconnection. To do so, we find the plasma parameters that locally drive reconnection in the magnetosheath and magnetosphere in planes perpendicular to the X line at a large number of points along the X line. The global magnetohydrodynamic simulations are from the three-dimensional Block-Adaptive, Tree Solarwind Roe-type Upwind Scheme (BATS-R-US) code with a uniform resistivity, although the techniques described here are extensible to any global magnetospheric simulation model. We find that the predicted local reconnection rates scale well with the measured values for all simulations, being nearly exact for due southward IMF. However, the absolute predictions differ by an undetermined constant of proportionality, whose magnitude increases as the IMF clock angle changes from southward to northward. We also show similar scaling agreement in a simulation with oblique southward IMF and a dipole tilt. The present results will be an important component of a full understanding of the local and global properties of dayside reconnection.

  11. The Local Stellar Velocity Field via Vector Spherical Harmonics

    NASA Technical Reports Server (NTRS)

    Makarov, V. V.; Murphy, D. W.

    2007-01-01

    We analyze the local field of stellar tangential velocities for a sample of 42,339 nonbinary Hipparcos stars with accurate parallaxes, using a vector spherical harmonic formalism.We derive simple relations between the parameters of the classical linear model (Ogorodnikov-Milne) of the local systemic field and low-degree terms of the general vector harmonic decomposition. Taking advantage of these relationships, we determine the solar velocity with respect to the local stars of (V(sub X), V(sub Y), V(sub Z)) = (10.5, 18.5, 7.3) +/- 0.1 km s(exp -1) not for the asymmetric drift with respect to the local standard of rest. If only stars more distant than 100 pc are considered, the peculiar solar motion is (V(sub X), V(sub Y), V(sub Z)) = (9.9, 15.6, 6.9) +/- 0.2 km s(exp -1). The adverse effects of harmonic leakage, which occurs between the reflex solar motion represented by the three electric vector harmonics in the velocity space and higher degree harmonics in the proper-motion space, are eliminated in our analysis by direct subtraction of the reflex solar velocity in its tangential components for each star...

  12. Local flow control for active building facades

    NASA Astrophysics Data System (ADS)

    Kaligotla, Srikar; Chen, Wayne; Glauser, Mark

    2010-11-01

    Existing building facade designs are for a passive and an impermeable shell to prevent migration of outdoor air into the building and to control heat transfers between the exterior environment and the building interior. An active facade that can respond in real time to changing environmental conditions like wind speed and direction, pollutant load, temperature, humidity and light can lower energy use and maximize occupant comfort. With an increased awareness of cost and environmental effects of energy use, cross or natural ventilation has become an attractive method to lower energy use. Separated flow regions around such buildings are undesirable due to high concentration of pollutants, especially if the vents or dynamic windows for cross ventilation are situated in these regions. Outside pollutant load redistribution through vents can be regulated via flow separation control to minimize transport of pollutants into the building. Flow separation has been substantially reduced with the application of intelligent flow control tools developed at Syracuse University for flow around "silo" (turret) like structures. Similar flow control models can be introduced into buildings with cross ventilation for local external flow separation control. Initial experiments will be performed for turbulent flow over a rectangular block (scaled to be a mid-rise building) that has been configured with dynamic vents and unsteady suction actuators in a wind tunnel at various wind speeds.

  13. Numerical simulations of localized high field 1H MR spectroscopy

    PubMed Central

    Kaiser, Lana G.; Young, Karl; Matson, Gerald B.

    2008-01-01

    The limited bandwidths of volume selective RF pulses in localized in vivo MRS experiments introduce spatial artifacts that complicate spectral quantification of J-coupled metabolites. These effects are commonly referred to as a spatial interference or “4 compartment” artifacts and are more pronounced at higher field strengths. The main focus of this study is to develop a generalized approach to numerical simulations that combines full density matrix calculations with 3D localization to investigate the spatial artifacts and to provide accurate prior knowledge for spectral fitting. Full density matrix calculations with 3D localization using experimental pulses were carried out for PRESS (TE=20, 70 ms), STEAM (TE=20, 70 ms) and LASER (TE=70 ms) pulse sequences and compared to non-localized simulations and to phantom solution data at 4 Tesla. Additional simulations at 1.5 and 7 Tesla were carried out for STEAM and PRESS (TE=20 ms). Four brain metabolites that represented a range from weak to strong J-coupling networks were included in the simulations (lactate, N-acetylaspartate, glutamate and myo-inositol). For longer TE, full 3D localization was necessary to achieve agreement between the simulations and phantom solution spectra for the majority of cases in all pulse sequence simulations. For short echo time (TE=20 ms), ideal pulses without localizing gradients gave results that were in agreement with phantom results at 4 T for STEAM, but not for PRESS (TE=20). Numerical simulations that incorporate volume localization using experimental RF pulses are shown to be a powerful tool for generation of accurate metabolic basis sets for spectral fitting and for optimization of experimental parameters. PMID:18789736

  14. Source localization of brain activity using helium-free interferometer

    NASA Astrophysics Data System (ADS)

    Dammers, Jürgen; Chocholacs, Harald; Eich, Eberhard; Boers, Frank; Faley, Michael; Dunin-Borkowski, Rafal E.; Jon Shah, N.

    2014-05-01

    To detect extremely small magnetic fields generated by the human brain, currently all commercial magnetoencephalography (MEG) systems are equipped with low-temperature (low-Tc) superconducting quantum interference device (SQUID) sensors that use liquid helium for cooling. The limited and increasingly expensive supply of helium, which has seen dramatic price increases recently, has become a real problem for such systems and the situation shows no signs of abating. MEG research in the long run is now endangered. In this study, we report a MEG source localization utilizing a single, highly sensitive SQUID cooled with liquid nitrogen only. Our findings confirm that localization of neuromagnetic activity is indeed possible using high-Tc SQUIDs. We believe that our findings secure the future of this exquisitely sensitive technique and have major implications for brain research and the developments of cost-effective multi-channel, high-Tc SQUID-based MEG systems.

  15. Source localization of brain activity using helium-free interferometer

    SciTech Connect

    Dammers, Jürgen Chocholacs, Harald; Eich, Eberhard; Boers, Frank; Faley, Michael; Dunin-Borkowski, Rafal E.; Jon Shah, N.

    2014-05-26

    To detect extremely small magnetic fields generated by the human brain, currently all commercial magnetoencephalography (MEG) systems are equipped with low-temperature (low-T{sub c}) superconducting quantum interference device (SQUID) sensors that use liquid helium for cooling. The limited and increasingly expensive supply of helium, which has seen dramatic price increases recently, has become a real problem for such systems and the situation shows no signs of abating. MEG research in the long run is now endangered. In this study, we report a MEG source localization utilizing a single, highly sensitive SQUID cooled with liquid nitrogen only. Our findings confirm that localization of neuromagnetic activity is indeed possible using high-T{sub c} SQUIDs. We believe that our findings secure the future of this exquisitely sensitive technique and have major implications for brain research and the developments of cost-effective multi-channel, high-T{sub c} SQUID-based MEG systems.

  16. Measuring Earth's Local Magnetic Field Using a Helmholtz Coil

    ERIC Educational Resources Information Center

    Williams, Jonathan E.

    2014-01-01

    In this paper, I present a low-cost interactive experiment for measuring the strength of Earth's local magnetic field. This activity can be done in most high schools or two-year physics laboratories with limited resources, yet will have a tremendous learning impact. This experiment solidifies the three-dimensional nature of Earth's…

  17. Local excitations in mean-field spin glasses

    NASA Astrophysics Data System (ADS)

    Krzakala, F.; Parisi, G.

    2004-06-01

    We address the question of geometrical as well as energetic properties of local excitations in mean-field Ising spin glasses. We study analytically the Random Energy Model and numerically a dilute mean-field model, first on tree-like graphs, equivalent to a replica-symmetric computation, and then directly on finite-connectivity random lattices. In the first model, characterized by a discontinuous replica symmetry breaking, we found that the energy of finite-volume excitation is infinite, whereas in the dilute mean-field model, described by a continuous replica symmetry breaking, it slowly decreases with sizes and saturates at a finite value, in contrast with what would be naively expected. The geometrical properties of these excitations are similar to those of lattice animals or branched polymers. We discuss the meaning of these results in terms of replica symmetry breaking and also possible relevance in finite-dimensional systems.

  18. Localized strain field measurement on laminography data with mechanical regularization

    NASA Astrophysics Data System (ADS)

    Taillandier-Thomas, Thibault; Roux, Stéphane; Morgeneyer, Thilo F.; Hild, François

    2014-04-01

    For an in-depth understanding of the failure of structural materials the study of deformation mechanisms in the material bulk is fundamental. In situ synchrotron computed laminography provides 3D images of sheet samples and digital volume correlation yields the displacement and strain fields between each step of experimental loading by using the natural contrast of the material. Difficulties arise from the lack of data, which is intrinsic to laminography and leads to several artifacts, and the little absorption contrast in the 3D image texture of the studied aluminum alloy. To lower the uncertainty level and to have a better mechanical admissibility of the measured displacement field, a regularized digital volume correlation procedure is introduced and applied to measure localized displacement and strain fields.

  19. New localization mechanism and Hodge duality for q -form field

    NASA Astrophysics Data System (ADS)

    Fu, Chun-E.; Liu, Yu-Xiao; Guo, Heng; Zhang, Sheng-Li

    2016-03-01

    In this paper, we investigate the problem of localization and the Hodge duality for a q -form field on a p -brane with codimension one. By a general Kaluza-Klein (KK) decomposition without gauge fixing, we obtain two Schrödinger-like equations for two types of KK modes of the bulk q -form field, which determine the localization and mass spectra of these KK modes. It is found that there are two types of zero modes (the 0-level modes): a q -form zero mode and a (q -1 )-form one, which cannot be localized on the brane at the same time. For the n -level KK modes, there are two interacting KK modes, a massive q -form KK mode and a massless (q -1 )-form one. By analyzing gauge invariance of the effective action and choosing a gauge condition, the n -level massive q -form KK mode decouples from the n -level massless (q -1 )-form one. It is also found that the Hodge duality in the bulk naturally becomes two dualities on the brane. The first one is the Hodge duality between a q -form zero mode and a (p -q -1 )-form one, or between a (q -1 )-form zero mode and a (p -q )-form one. The second duality is between two group KK modes: one is an n -level massive q -form KK mode with mass mn and an n -level massless (q -1 )-form mode; another is an n -level (p -q )-form one with the same mass mn and an n -level massless (p -q -1 )-form mode. Because of the dualities, the effective field theories on the brane for the KK modes of the two dual bulk form fields are physically equivalent.

  20. Localized magnetic fields enhance the field sensitivity of the gyrotropic resonance frequency of a magnetic vortex

    NASA Astrophysics Data System (ADS)

    Fried, Jasper P.; Metaxas, Peter J.

    2016-02-01

    We have carried out micromagnetic simulations of the gyrotropic resonance mode of a magnetic vortex in the presence of spatially localized and spatially uniform out-of-plane magnetic fields. We show that the field-induced change in the gyrotropic mode frequency is significantly larger when the field is centrally localized over lengths which are comparable to or a few times larger than the vortex core radius. When aligned with the core magnetization, such fields generate an additional confinement of the core. This confinement increases the vortex stiffness in the small-displacement limit, leading to a resonance shift which is greater than that expected for a uniform out-of-plane field of the same amplitude. Fields generated by uniformly magnetized spherical particles having a fixed separation from the disk are found to generate analogous effects except that there is a maximum in the shift at intermediate particle sizes where field localization and stray field magnitude combine optimally to generate a maximum confinement.

  1. Near-Field Source Localization by Using Focusing Technique

    NASA Astrophysics Data System (ADS)

    He, Hongyang; Wang, Yide; Saillard, Joseph

    2008-12-01

    We discuss two fast algorithms to localize multiple sources in near field. The symmetry-based method proposed by Zhi and Chia (2007) is first improved by implementing a search-free procedure for the reduction of computation cost. We present then a focusing-based method which does not require symmetric array configuration. By using focusing technique, the near-field signal model is transformed into a model possessing the same structure as in the far-field situation, which allows the bearing estimation with the well-studied far-field methods. With the estimated bearing, the range estimation of each source is consequently obtained by using 1D MUSIC method without parameter pairing. The performance of the improved symmetry-based method and the proposed focusing-based method is compared by Monte Carlo simulations and with Crammer-Rao bound as well. Unlike other near-field algorithms, these two approaches require neither high-computation cost nor high-order statistics.

  2. Electron Spin Resonance Imaging Utilizing Localized Microwave Magnetic Field

    NASA Astrophysics Data System (ADS)

    Furusawa, Masahiro; Ikeya, Motoji

    1990-02-01

    A method for two-dimensional electron spin resonance (ESR) imaging utilizing a localized microwave field is presented with an application of the image processing technique. Microwaves are localized at the surface of a sample by placing a sample in contact with a pinholed cavity wall. A two-dimensional ESR image can be obtained by scanning the sample in contact with the cavity. Some ESR images which correspond to distribution of natural radiation damages and paramagnetic impurities in carbonate fossils of a crinoid and an ammonite are presented as applications in earth science. Resolution of a raw ESR image is restricted by the diameter of the hole (1 mm). Higher resolution of 0.2 mm is obtained by using a deconvolution algorithm and instrument function for the hole. Restored images of a test sample of DPPH and of a fossil crinoid are presented.

  3. Quantization of non-local field theory and string field theory

    NASA Astrophysics Data System (ADS)

    Hata, Hiroyuki

    1989-02-01

    The interaction vertex in covariant string field theory (SFT) is non-local in the time coordinate and the conventional canonical quantization is inapplicable to it. As an approach to quantizing this system we apply Hayashi's theory of the Hamilton formalism for field theories with non-local interactions. We find that the resulting one-loop amplitudes in covariant closed SFT coincide with those in the light-cone gauge SFT. I would like to thank T. Kugo, H. Kunitomo, M.M. Nojiri, K. Ogawa and K. Suehiro for valuable discussions, and especially Professor S. Tanaka for directing my attention to Hayashi's theory.

  4. Exponentially localized Wannier functions in periodic zero flux magnetic fields

    NASA Astrophysics Data System (ADS)

    De Nittis, G.; Lein, M.

    2011-11-01

    In this work, we investigate conditions which ensure the existence of an exponentially localized Wannier basis for a given periodic hamiltonian. We extend previous results [Panati, G., Ann. Henri Poincare 8, 995-1011 (2007), 10.1007/s00023-007-0326-8] to include periodic zero flux magnetic fields which is the setting also investigated by Kuchment [J. Phys. A: Math. Theor. 42, 025203 (2009), 10.1088/1751-8113/42/2/025203]. The new notion of magnetic symmetry plays a crucial rôle; to a large class of symmetries for a non-magnetic system, one can associate "magnetic" symmetries of the related magnetic system. Observing that the existence of an exponentially localized Wannier basis is equivalent to the triviality of the so-called Bloch bundle, a rank m hermitian vector bundle over the Brillouin zone, we prove that magnetic time-reversal symmetry is sufficient to ensure the triviality of the Bloch bundle in spatial dimension d = 1, 2, 3. For d = 4, an exponentially localized Wannier basis exists provided that the trace per unit volume of a suitable function of the Fermi projection vanishes. For d > 4 and d ⩽ 2m (stable rank regime) only the exponential localization of a subset of Wannier functions is shown; this improves part of the analysis of Kuchment [J. Phys. A: Math. Theor. 42, 025203 (2009), 10.1088/1751-8113/42/2/025203]. Finally, for d > 4 and d > 2m (unstable rank regime) we show that the mere analysis of Chern classes does not suffice in order to prove triviality and thus exponential localization.

  5. On the Local-Field Distribution in Attractor Neural Networks

    NASA Astrophysics Data System (ADS)

    Korutcheva, E.; Koroutchev, K.

    In this paper a simple two-layer neural network's model, similar to that studied by D. Amit and N. Brunel,11 is investigated in the frames of the mean-field approximation. The distributions of the local fields are analytically derived and compared to those obtained in Ref. 11. The dynamic properties are discussed and the basin of attraction in some parametric space is found. A procedure for driving the system into a basin of attraction by using a regulation imposed on the network is proposed. The effect of outer stimulus is shown to have a destructive influence on the attractor, forcing the latter to disappear if the distribution of the stimulus has high enough variance or if the stimulus has a spatial structure with sufficient contrast. The techniques, used in this paper, for obtaining the analytical results can be applied to more complex topologies of linked recurrent neural networks.

  6. 21 CFR 346.10 - Local anesthetic active ingredients.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 5 2010-04-01 2010-04-01 false Local anesthetic active ingredients. 346.10 Section 346.10 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES... § 346.10 Local anesthetic active ingredients. The active ingredient of the product consists of any...

  7. 21 CFR 346.10 - Local anesthetic active ingredients.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 5 2013-04-01 2013-04-01 false Local anesthetic active ingredients. 346.10 Section 346.10 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES... § 346.10 Local anesthetic active ingredients. The active ingredient of the product consists of any...

  8. 21 CFR 346.10 - Local anesthetic active ingredients.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 5 2012-04-01 2012-04-01 false Local anesthetic active ingredients. 346.10 Section 346.10 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES... § 346.10 Local anesthetic active ingredients. The active ingredient of the product consists of any...

  9. 21 CFR 346.10 - Local anesthetic active ingredients.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 5 2014-04-01 2014-04-01 false Local anesthetic active ingredients. 346.10 Section 346.10 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES... § 346.10 Local anesthetic active ingredients. The active ingredient of the product consists of any...

  10. 21 CFR 346.10 - Local anesthetic active ingredients.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 5 2011-04-01 2011-04-01 false Local anesthetic active ingredients. 346.10 Section 346.10 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES... § 346.10 Local anesthetic active ingredients. The active ingredient of the product consists of any...

  11. 24 CFR 4100.3 - Field activities.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 24 Housing and Urban Development 5 2014-04-01 2014-04-01 false Field activities. 4100.3 Section 4100.3 Housing and Urban Development Regulations Relating to Housing and Urban Development (Continued) NEIGHBORHOOD REINVESTMENT CORPORATION ORGANIZATION AND CHANNELING OF FUNCTIONS § 4100.3 Field activities....

  12. Influence of magnetic field on electric-field-induced local polar states in manganites

    NASA Astrophysics Data System (ADS)

    Mamin, R. F.; Strle, J.; Bizyaev, D. A.; Yusupov, R. V.; Kabanov, V. V.; Kranjec, A.; Borovsak, M.; Mihailovic, D.; Bukharaev, A. A.

    2015-11-01

    It is shown that creation of local charged states at the surface of the lanthanum-strontium manganite single crystals by means of bias application via a conducting atomic force microscope tip is strongly affected by magnetic field. Both a charge and a size of created structures increase significantly on application of the magnetic field during the induction. We argue that the observed phenomenon originates from a known tendency of manganites toward charge segregation and its intimate relation to magnetic ordering.

  13. Influence of magnetic field on electric-field-induced local polar states in manganites

    SciTech Connect

    Mamin, R. F.; Strle, J.; Kabanov, V. V.; Kranjec, A.; Borovsak, M.; Mihailovic, D.; Bizyaev, D. A.; Yusupov, R. V.; Bukharaev, A. A.

    2015-11-09

    It is shown that creation of local charged states at the surface of the lanthanum-strontium manganite single crystals by means of bias application via a conducting atomic force microscope tip is strongly affected by magnetic field. Both a charge and a size of created structures increase significantly on application of the magnetic field during the induction. We argue that the observed phenomenon originates from a known tendency of manganites toward charge segregation and its intimate relation to magnetic ordering.

  14. Deviations from the local field approximation in negative streamer heads

    NASA Astrophysics Data System (ADS)

    Li, Chao; Brok, W. J. M.; Ebert, Ute; van der Mullen, J. J. A. M.

    2007-06-01

    Negative streamer ionization fronts in nitrogen under normal conditions are investigated both in a particle model and in a fluid model in local field approximation. The parameter functions for the fluid model are derived from swarm experiments in the particle model. The front structure on the inner scale is investigated in a one-dimensional setting, allowing reasonable run time and memory consumption and high numerical accuracy without introducing superparticles. If the reduced electric field immediately before the front is ⩽50kV/(cmbar), solutions of fluid and particle model agree very well. If the field increases up to 200kV/(cmbar), the solutions of particle and fluid model deviate, in particular, the ionization level behind the front becomes up to 60% higher in the particle model while the velocity is rather insensitive. Particle and fluid model deviate because electrons with high energies do not yet fully run away from the front, but are somewhat ahead. This leads to increasing ionization rates in the particle model at the very tip of the front. The energy overshoot of electrons in the leading edge of the front actually agrees quantitatively with the energy overshoot in the leading edge of an electron swarm or avalanche in the same electric field.

  15. Polarity establishment requires localized activation of Cdc42

    PubMed Central

    Woods, Benjamin; Kuo, Chun-Chen; Wu, Chi-Fang; Zyla, Trevin R.

    2015-01-01

    Establishment of cell polarity in animal and fungal cells involves localization of the conserved Rho-family guanosine triphosphatase, Cdc42, to the cortical region destined to become the “front” of the cell. The high local concentration of active Cdc42 promotes cytoskeletal polarization through various effectors. Cdc42 accumulation at the front is thought to involve positive feedback, and studies in the budding yeast Saccharomyces cerevisiae have suggested distinct positive feedback mechanisms. One class of mechanisms involves localized activation of Cdc42 at the front, whereas another class involves localized delivery of Cdc42 to the front. Here we show that Cdc42 activation must be localized for successful polarity establishment, supporting local activation rather than local delivery as the dominant mechanism in this system. PMID:26459595

  16. Localized electric field of plasmonic nanoplatform enhanced photodynamic tumor therapy.

    PubMed

    Li, Yiye; Wen, Tao; Zhao, Ruifang; Liu, Xixi; Ji, Tianjiao; Wang, Hai; Shi, Xiaowei; Shi, Jian; Wei, Jingyan; Zhao, Yuliang; Wu, Xiaochun; Nie, Guangjun

    2014-11-25

    Near-infrared plasmonic nanoparticles demonstrate great potential in disease theranostic applications. Herein a nanoplatform, composed of mesoporous silica-coated gold nanorods (AuNRs), is tailor-designed to optimize the photodynamic therapy (PDT) for tumor based on the plasmonic effect. The surface plasmon resonance of AuNRs was fine-tuned to overlap with the exciton absorption of indocyanine green (ICG), a near-infrared photodynamic dye with poor photostability and low quantum yield. Such overlap greatly increases the singlet oxygen yield of incorporated ICG by maximizing the local field enhancement, and protecting the ICG molecules against photodegradation by virtue of the high absorption cross section of the AuNRs. The silica shell strongly increased ICG payload with the additional benefit of enhancing ICG photostability by facilitating the formation of ICG aggregates. As-fabricated AuNR@SiO2-ICG nanoplatform enables trimodal imaging, near-infrared fluorescence from ICG, and two-photon luminescence/photoacoustic tomography from the AuNRs. The integrated strategy significantly improved photodynamic destruction of breast tumor cells and inhibited the growth of orthotopic breast tumors in mice, with mild laser irradiation, through a synergistic effect of PDT and photothermal therapy. Our study highlights the effect of local field enhancement in PDT and demonstrates the importance of systematic design of nanoplatform to greatly enhancing the antitumor efficacy. PMID:25375193

  17. Matched field localization based on CS-MUSIC algorithm

    NASA Astrophysics Data System (ADS)

    Guo, Shuangle; Tang, Ruichun; Peng, Linhui; Ji, Xiaopeng

    2016-04-01

    The problem caused by shortness or excessiveness of snapshots and by coherent sources in underwater acoustic positioning is considered. A matched field localization algorithm based on CS-MUSIC (Compressive Sensing Multiple Signal Classification) is proposed based on the sparse mathematical model of the underwater positioning. The signal matrix is calculated through the SVD (Singular Value Decomposition) of the observation matrix. The observation matrix in the sparse mathematical model is replaced by the signal matrix, and a new concise sparse mathematical model is obtained, which means not only the scale of the localization problem but also the noise level is reduced; then the new sparse mathematical model is solved by the CS-MUSIC algorithm which is a combination of CS (Compressive Sensing) method and MUSIC (Multiple Signal Classification) method. The algorithm proposed in this paper can overcome effectively the difficulties caused by correlated sources and shortness of snapshots, and it can also reduce the time complexity and noise level of the localization problem by using the SVD of the observation matrix when the number of snapshots is large, which will be proved in this paper.

  18. The Local Stellar Velocity Field via Vector Spherical Harmonics

    NASA Astrophysics Data System (ADS)

    Makarov, V. V.; Murphy, D. W.

    2007-07-01

    We analyze the local field of stellar tangential velocities for a sample of 42,339 nonbinary Hipparcos stars with accurate parallaxes, using a vector spherical harmonic formalism. We derive simple relations between the parameters of the classical linear model (Ogorodnikov-Milne) of the local systemic field and low-degree terms of the general vector harmonic decomposition. Taking advantage of these relationships, we determine the solar velocity with respect to the local stars of (VX,VY,VZ)=(10.5,18.5,7.3)+/-0.1 km s-1 not corrected for the asymmetric drift with respect to the local standard of rest. If only stars more distant than 100 pc are considered, the peculiar solar motion is (VX,VY,VZ)=(9.9,15.6,6.9)+/-0.2 km s-1. The adverse effects of harmonic leakage, which occurs between the reflex solar motion represented by the three electric vector harmonics in the velocity space and higher degree harmonics in the proper-motion space, are eliminated in our analysis by direct subtraction of the reflex solar velocity in its tangential components for each star. The Oort parameters determined by a straightforward least-squares adjustment in vector spherical harmonics are A=14.0+/-1.4, B=-13.1+/-1.2, K=1.1+/-1.8, and C=-2.9+/-1.4 km s-1 kpc-1. The physical meaning and the implications of these parameters are discussed in the framework of a general linear model of the velocity field. We find a few statistically significant higher degree harmonic terms that do not correspond to any parameters in the classical linear model. One of them, a third-degree electric harmonic, is tentatively explained as the response to a negative linear gradient of rotation velocity with distance from the Galactic plane, which we estimate at ~-20 km s-1 kpc-1. A similar vertical gradient of rotation velocity has been detected for more distant stars representing the thick disk (z>1 kpc), but here we surmise its existence in the thin disk at z<200 pc. The most unexpected and unexplained term within

  19. The Local Stellar Velocity Field via Vector Spherical Harmonics

    NASA Technical Reports Server (NTRS)

    Markarov, V. V.; Murphy, D. W.

    2007-01-01

    We analyze the local field of stellar tangential velocities for a sample of 42,339 nonbinary Hipparcos stars with accurate parallaxes, using a vector spherical harmonic formalism. We derive simple relations between the parameters of the classical linear model (Ogorodnikov-Milne) of the local systemic field and low-degree terms of the general vector harmonic decomposition. Taking advantage of these relationships, we determine the solar velocity with respect to the local stars of (V(sub X), V(sub Y), V(sub Z)) (10.5, 18.5, 7.3) +/- 0.1 km s(exp -1) not corrected for the asymmetric drift with respect to the local standard of rest. If only stars more distant than 100 pc are considered, the peculiar solar motion is (V(sub X), V(sub Y), V(sub Z)) (9.9, 15.6, 6.9) +/- 0.2 km s(exp -1). The adverse effects of harmonic leakage, which occurs between the reflex solar motion represented by the three electric vector harmonics in the velocity space and higher degree harmonics in the proper-motion space, are eliminated in our analysis by direct subtraction of the reflex solar velocity in its tangential components for each star. The Oort parameters determined by a straightforward least-squares adjustment in vector spherical harmonics are A=14.0 +/- 1.4, B=13.1 +/- 1.2, K=1.1 +/- 1.8, and C=2.9 +/- 1.4 km s(exp -1) kpc(exp -1). The physical meaning and the implications of these parameters are discussed in the framework of a general linear model of the velocity field. We find a few statistically significant higher degree harmonic terms that do not correspond to any parameters in the classical linear model. One of them, a third-degree electric harmonic, is tentatively explained as the response to a negative linear gradient of rotation velocity with distance from the Galactic plane, which we estimate at approximately -20 km s(exp -1) kpc(exp -1). A similar vertical gradient of rotation velocity has been detected for more distant stars representing the thick disk (z greater than 1 kpc

  20. Time-localized projectors in string field theory with an E-field

    SciTech Connect

    Maccaferri, C.; Scherer Santos, R.J.; Tolla, D.D.

    2005-03-15

    We extend the analysis of Bonora et al. [hep-th/0409063] to the case of a constant electric field turned on the world volume and on a transverse direction of a D-brane. We show that time localization is still obtained by inverting the discrete eigenvalues of the lump solution. The lifetime of the unstable soliton is shown to depend on two free parameters: the b parameter and the value of the electric field. As a by-product, we construct the normalized diagonal basis of the star algebra in the B{sub {mu}}{sub {nu}}-field background.

  1. Localizing a large-dimensional field of sonobuoys

    NASA Astrophysics Data System (ADS)

    Collison, Nicole E.; Dosso, Stan E.

    2003-04-01

    For target localization, multistatic sonar systems require an adequate knowledge of both the source and receiver positions. In this paper, we use a regularized acoustic inversion method on measured direct-arrival times from several impulsive sources to track a freely drifting sonobuoy field. The shallow-water experiment involved 11 sonobuoys within a 6×8 km field, with 6 sources over approximately 70 min. Regularization allows prior information to be built into the inversion, which in this case consists of estimates (with associated uncertainties) of the source and initial sonobuoy drop positions determined from the GPS position of the aircraft at the instant of drop, as well as a model for smooth sonobuoy tracks. Closely spaced sonobuoys move along similar tracks, although there is considerable movement in different directions over the entire field (260-700 m). Positioning uncertainties are estimated using a Monte Carlo appraisal procedure to be approximately 100 m (absolute) and 65 m (relative). Submitted for the Signal Processing Young Presenter Award.

  2. Locality of Gravitational Systems from Entanglement of Conformal Field Theories.

    PubMed

    Lin, Jennifer; Marcolli, Matilde; Ooguri, Hirosi; Stoica, Bogdan

    2015-06-01

    The Ryu-Takayanagi formula relates the entanglement entropy in a conformal field theory to the area of a minimal surface in its holographic dual. We show that this relation can be inverted for any state in the conformal field theory to compute the bulk stress-energy tensor near the boundary of the bulk spacetime, reconstructing the local data in the bulk from the entanglement on the boundary. We also show that positivity, monotonicity, and convexity of the relative entropy for small spherical domains between the reduced density matrices of any state and of the ground state of the conformal field theory are guaranteed by positivity conditions on the bulk matter energy density. As positivity and monotonicity of the relative entropy are general properties of quantum systems, this can be interpreted as a derivation of bulk energy conditions in any holographic system for which the Ryu-Takayanagi prescription applies. We discuss an information theoretical interpretation of the convexity in terms of the Fisher metric. PMID:26196612

  3. High-Resolution Local Crustal Magnetic Field Modeling of the Martian South Pole

    NASA Astrophysics Data System (ADS)

    Plattner, A.; Simons, F. J.

    2014-12-01

    The Mars Global Surveyor (MGS) satellite mission has brought us a wealth of information about the Martian magnetic field. Besides determining that Mars currently does not possess an active core field, MGS revealed that Mars contains an unexpectedly wide crustal magnetic field intensity range. In its orbit insertion, MGS performed a series of low altitude passes down to around 100 km above surface. During this mission phase the magnetic field measurements were active. In particular the nighttime low-altitude data are of high interest because they contain minimal noise from solar wind. Since these data only cover a small portion of the planet's surface, to date all Martian crustal magnetic field models blend the highest-quality data with lower quality measurements collected either at higher satellite altitudes or during daytime. In this contribution we present a locally inverted crustal magnetic field model for the Martian South Polar region calculated from only the highest-quality MGS data using locally constructed altitude vector Slepian functions. The South Polar region of Mars contains the southern part of the strongly magnetized Terra Sirenum and the area south of the Tharsis volcanic highland. Besides parts of planetary scale features our area of data coverage also contains local features such as the presumably volcanic Australe Montes and the Prometheus impact crater. These ingredients compose a highly heterogeneous crustal magnetic field. We show that even for our dense low-altitude low-noise data set the inversion for the crustal magnetic field of a weakly magnetized region adjacent to a region containing a strong magnetic field leads to artifacts in the weak region. With our local method we can avoid these artifacts by selecting subregions of roughly homogeneous field intensity and individually invert for crustal magnetic fields from data within only these subregions. This regional and subregional modeling allows us to reveal previously obscured crustal

  4. Past Activeness, Solidarity, and Local Development Efforts.

    ERIC Educational Resources Information Center

    Zekeri, Andrew A.; And Others

    1994-01-01

    Draws upon community field theory and human ecology and uses data from 120 rural Pennsylvania school districts to examine the relative contributions of past community actions, development of solidarity, and ecological variables (socioeconomic status, remoteness, previous industrialization, and percentage of residents commuting to work) to the…

  5. Spin resonance strength of a localized rf magnetic field

    NASA Astrophysics Data System (ADS)

    Lee, S. Y.

    2006-07-01

    Spin-resonance strength produced by a localized rf field has been a focus of recent publications [V. S. Morozov , Phys. Rev. ST Accel. Beams 7, 024002 (2004).PRABFM1098-440210.1103/PhysRevSTAB.7.024002; M. A. Leonova (to be published).; T. Roser, in Handbook of Accelerator Physics and Engineering, edited by A. W. Chao and M. Tigner (World Scientific, Singapore, 1999), p. 151.; M. Bai, W. W. MacKay, and T. Roser, Phys. Rev. ST Accel. Beams 8, 099001 (2005).PRABFM1098-440210.1103/PhysRevSTAB.8.099001; V. S. Morozov , Phys. Rev. ST Accel. Beams 8, 099002 (2005).PRABFM1098-440210.1103/PhysRevSTAB.8.099002]. This paper discusses the debated factor of 2, and provides a formula to calculate the component enhanced by the induced betatron motion.

  6. Wedge-Local Fields in Integrable Models with Bound States

    NASA Astrophysics Data System (ADS)

    Cadamuro, Daniela; Tanimoto, Yoh

    2015-12-01

    Recently, large families of two-dimensional quantum field theories with factorizing S-matrices have been constructed by the operator-algebraic methods, by first showing the existence of observables localized in wedge-shaped regions. However, these constructions have been limited to the class of S-matrices whose components are analytic in rapidity in the physical strip. In this work, we construct candidates for observables in wedges for scalar factorizing S-matrices with poles in the physical strip and show that they weakly commute on a certain domain. We discuss some technical issues concerning further developments, especially the self-adjointness of the candidate operators here and strong commutativity between them.

  7. Probing {N}=2 superconformal field theories with localization

    NASA Astrophysics Data System (ADS)

    Fiol, Bartomeu; Garolera, Blai; Torrentsa, Genís

    2016-01-01

    We use supersymmetric localization to study probes of four dimensional Lagrangian {N}=2 superconformal field theories. We first derive a unique equation for the eigenvalue density of these theories. We observe that these theories have a Wigner eigenvalue density precisely when they satisfy a necessary condition for having a holographic dual with a sensible higher-derivative expansion. We then compute in the saddle-point approximation the vacuum expectation value of 1/2-BPS circular Wilson loops, and the two-point functions of these Wilson loops with the Lagrangian density and with the stress-energy tensor. This last computation also provides the corresponding Bremsstrahlung functions and entanglement entropies. As expected, whenever a finite fraction of the matter is in the fundamental representation, the results are drastically different from those of {N}=4 supersymmetric Yang-Mills theory.

  8. Neural field dynamics under variation of local and global connectivity and finite transmission speed

    NASA Astrophysics Data System (ADS)

    Qubbaj, Murad R.; Jirsa, Viktor K.

    2009-12-01

    Spatially continuous networks with heterogeneous connections are ubiquitous in biological systems, in particular neural systems. To understand the mutual effects of locally homogeneous and globally heterogeneous connectivity, we investigate the stability of the steady state activity of a neural field as a function of its connectivity. The variation of the connectivity is implemented through manipulation of a heterogeneous two-point connection embedded into the otherwise homogeneous connectivity matrix and by variation of the connectivity strength and transmission speed. Detailed examples including the Ginzburg-Landau equation and various other local architectures are discussed. Our analysis shows that developmental changes such as the myelination of the cortical large-scale fiber system generally result in the stabilization of steady state activity independent of the local connectivity. Non-oscillatory instabilities are shown to be independent of any influences of time delay.

  9. Field Effect and Strongly Localized Carriers in the Metal-Insulator Transition Material VO(2).

    PubMed

    Martens, K; Jeong, J W; Aetukuri, N; Rettner, C; Shukla, N; Freeman, E; Esfahani, D N; Peeters, F M; Topuria, T; Rice, P M; Volodin, A; Douhard, B; Vandervorst, W; Samant, M G; Datta, S; Parkin, S S P

    2015-11-01

    The intrinsic field effect, the change in surface conductance with an applied transverse electric field, of prototypal strongly correlated VO(2) has remained elusive. Here we report its measurement enabled by epitaxial VO(2) and atomic layer deposited high-κ dielectrics. Oxygen migration, joule heating, and the linked field-induced phase transition are precluded. The field effect can be understood in terms of field-induced carriers with densities up to ∼5×10(13)  cm(-2) which are trongly localized, as shown by their low, thermally activated mobility (∼1×10(-3)  cm(2)/V s at 300 K). These carriers show behavior consistent with that of Holstein polarons and strongly impact the (opto)electronics of VO(2). PMID:26588400

  10. Imaging local electric fields produced upon synchrotron X-ray exposure

    PubMed Central

    Dettmar, Christopher M.; Newman, Justin A.; Toth, Scott J.; Becker, Michael; Fischetti, Robert F.; Simpson, Garth J.

    2015-01-01

    Electron–hole separation following hard X-ray absorption during diffraction analysis of soft materials under cryogenic conditions produces substantial local electric fields visualizable by second harmonic generation (SHG) microscopy. Monte Carlo simulations of X-ray photoelectron trajectories suggest the formation of substantial local electric fields in the regions adjacent to those exposed to X-rays, indicating a possible electric-field–induced SHG (EFISH) mechanism for generating the observed signal. In studies of amorphous vitreous solvents, analysis of the SHG spatial profiles following X-ray microbeam exposure was consistent with an EFISH mechanism. Within protein crystals, exposure to 12-keV (1.033-Å) X-rays resulted in increased SHG in the region extending ∼3 μm beyond the borders of the X-ray beam. Moderate X-ray exposures typical of those used for crystal centering by raster scanning through an X-ray beam were sufficient to produce static electric fields easily detectable by SHG. The X-ray–induced SHG activity was observed with no measurable loss for longer than 2 wk while maintained under cryogenic conditions, but disappeared if annealed to room temperature for a few seconds. These results provide direct experimental observables capable of validating simulations of X-ray–induced damage within soft materials. In addition, X-ray–induced local fields may potentially impact diffraction resolution through localized piezoelectric distortions of the lattice. PMID:25552555

  11. Texaphyrins: Tumor Localizing Redox Active Expanded Porphyrins

    PubMed Central

    Arambula, Jonathan F.; Preihs, Christian; Borthwick, Derric; Magda, Darren; Sessler, Jonathan L.

    2011-01-01

    Texaphyrins, a class of tumor selective expanded porphyrins capable of coordinating large metals, have been found to act as redox mediators within biological systems. This review summarizes studies involving their experimentaluse in cancer chemotherapy. Mechanistic insights involving their presumed mode of action are also described, as well as certain structure activity relationships. Finally, newer texaphyrin-based applications associated with targeted drug delivery are presented. PMID:21355841

  12. Localization of cerebral activity during simple singing.

    PubMed

    Perry, D W; Zatorre, R J; Petrides, M; Alivisatos, B; Meyer, E; Evans, A C

    1999-11-01

    Cerebral blood flow (CBF) was measured with PET during rudimentary singing of a single pitch and vowel, contrasted to passive listening to complex tones. CBF increases in cortical areas related to motor control were seen in the supplementary motor area, anterior cingulate cortex, precentral gyri, anterior insula (and the adjacent inner face of the precentral operculum) and cerebellum, replicating most previously seen during speech. Increases in auditory cortex were seen within right Heschl's gyrus, and in the posterior superior temporal plane (and the immediately overlying parietal cortex). Since cortex near right Heschl's has been linked to complex pitch perception, its asymmetric activation here may be related to analyzing the fundamental frequency of one's own voice for feedback-guided modulation. PMID:10599861

  13. Localization of cerebral activity during simple singing.

    PubMed

    Perry, D W; Zatorre, R J; Petrides, M; Alivisatos, B; Meyer, E; Evans, A C

    1999-12-16

    Cerebral blood flow (CBF) was measured with PET during rudimentary singing of a single pitch and vowel, contrasted to passive listening to complex tones. CBF increases in cortical areas related to motor control were seen in the supplementary motor area, anterior cingulate cortex, precentral gyri, anterior insula (and the adjacent inner face of the precentral operculum) and cerebellum, replicating most previously seen during speech. Increases in auditory cortex were seen within right Heschl's gyrus, and in the posterior superior temporal plane (and the immediately overlying parietal cortex). Since cortex near right Heschl's has been linked to complex pitch perception, its asymmetric activation here may be related to analyzing the fundamental frequency of one's own voice for feedback-guided modulation. PMID:10716244

  14. Fluctuating magnetic field induced resonant activation

    SciTech Connect

    Mondal, Shrabani; Das, Sudip; Baura, Alendu; Bag, Bidhan Chandra

    2014-12-14

    In this paper, we have studied the properties of a Brownian particle at stationary state in the presence of a fluctuating magnetic field. Time dependence of the field makes the system thermodynamically open. As a signature of that the steady state distribution function becomes function of damping strength, intensity of fluctuations and constant parts of the applied magnetic field. It also depends on the correlation time of the fluctuating magnetic field. Our another observation is that the random magnetic field can induce the resonant activation phenomenon. Here correlation time is increased under the fixed variance of the fluctuating field. But if the correlation time (τ) increases under the fixed field strength then the mean first passage time rapidly grows at low τ and it almost converges at other limit. This is sharp contrast to the usual colored noise driven open system case where the mean first passage time diverges exponentially. We have also observed that a giant enhancement of barrier crossing rate occurs particularly at large strength of constant parts of the applied magnetic field even for very weak fluctuating magnetic field. Finally, break down of the Arrhenius result and disappearance of the Kramers’ turn over phenomenon may occur in the presence of a fluctuating magnetic field.

  15. Joint analysis of spikes and local field potentials using copula.

    PubMed

    Hu, Meng; Li, Mingyao; Li, Wu; Liang, Hualou

    2016-06-01

    Recent technological advances, which allow for simultaneous recording of spikes and local field potentials (LFPs) at multiple sites in a given cortical area or across different areas, have greatly increased our understanding of signal processing in brain circuits. Joint analysis of simultaneously collected spike and LFP signals is an important step to explicate how the brain orchestrates information processing. In this contribution, we present a novel statistical framework based on Gaussian copula to jointly model spikes and LFP. In our approach, we use copula to link separate, marginal regression models to construct a joint regression model, in which the binary-valued spike train data are modeled using generalized linear model (GLM) and the continuous-valued LFP data are modeled using linear regression. Model parameters can be efficiently estimated via maximum-likelihood. In particular, we show that our model offers a means to statistically detect directional influence between spikes and LFP, akin to Granger causality measure, and that we are able to assess its statistical significance by conducting a Wald test. Through extensive simulations, we also show that our method is able to reliably recover the true model used to generate the data. To demonstrate the effectiveness of our approach in real setting, we further apply the method to a mixed neural dataset, consisting of spikes and LFP simultaneously recorded from the visual cortex of a monkey performing a contour detection task. PMID:27012500

  16. Performance of FFT methods in local gravity field modelling

    NASA Technical Reports Server (NTRS)

    Forsberg, Rene; Solheim, Dag

    1989-01-01

    Fast Fourier transform (FFT) methods provide a fast and efficient means of processing large amounts of gravity or geoid data in local gravity field modelling. The FFT methods, however, has a number of theoretical and practical limitations, especially the use of flat-earth approximation, and the requirements for gridded data. In spite of this the method often yields excellent results in practice when compared to other more rigorous (and computationally expensive) methods, such as least-squares collocation. The good performance of the FFT methods illustrate that the theoretical approximations are offset by the capability of taking into account more data in larger areas, especially important for geoid predictions. For best results good data gridding algorithms are essential. In practice truncated collocation approaches may be used. For large areas at high latitudes the gridding must be done using suitable map projections such as UTM, to avoid trivial errors caused by the meridian convergence. The FFT methods are compared to ground truth data in New Mexico (xi, eta from delta g), Scandinavia (N from delta g, the geoid fits to 15 cm over 2000 km), and areas of the Atlantic (delta g from satellite altimetry using Wiener filtering). In all cases the FFT methods yields results comparable or superior to other methods.

  17. Motor task event detection using Subthalamic Nucleus Local Field Potentials.

    PubMed

    Niketeghad, Soroush; Hebb, Adam O; Nedrud, Joshua; Hanrahan, Sara J; Mahoor, Mohammad H

    2015-08-01

    Deep Brain Stimulation (DBS) provides significant therapeutic benefit for movement disorders such as Parkinson's disease. Current DBS devices lack real-time feedback (thus are open loop) and stimulation parameters are adjusted during scheduled visits with a clinician. A closed-loop DBS system may reduce power consumption and DBS side effects. In such systems, DBS parameters are adjusted based on patient's behavior, which means that behavior detection is a major step in designing such systems. Various physiological signals can be used to recognize the behaviors. Subthalamic Nucleus (STN) Local Field Potential (LFP) is a great candidate signal for the neural feedback, because it can be recorded from the stimulation lead and does not require additional sensors. A practical behavior detection method should be able to detect behaviors asynchronously meaning that it should not use any prior knowledge of behavior onsets. In this paper, we introduce a behavior detection method that is able to asynchronously detect the finger movements of Parkinson patients. As a result of this study, we learned that there is a motor-modulated inter-hemispheric connectivity between LFP signals recorded bilaterally from STN. We used non-linear regression method to measure this connectivity and use it to detect the finger movements. Performance of this method is evaluated using Receiver Operating Characteristic (ROC). PMID:26737550

  18. Extraction of bistable-percept-related features from local field potential by integration of local regression and common spatial patterns.

    PubMed

    Wang, Zhisong; Maier, Alexander; Logothetis, Nikos K; Liang, Hualou

    2009-08-01

    Bistable perception arises when an ambiguous stimulus under continuous view is perceived as an alternation of two mutually exclusive states. Such a stimulus provides a unique opportunity for understanding the neural basis of visual perception because it dissociates the perception from the visual input. In this paper, we focus on extracting the percept-related features from the local field potential (LFP) in monkey visual cortex for decoding its bistable structure-from-motion (SFM) perception. Our proposed feature extraction approach consists of two stages. First, we estimate and remove from each LFP trial the nonpercept-related stimulus-evoked activity via a local regression method called the locally weighted scatterplot smoothing because of the dissociation between the perception and the stimulus in our experimental paradigm. Second, we use the common spatial patterns approach to design spatial filters based on the residue signals of multiple channels to extract the percept-related features. We exploit a support vector machine (SVM) classifier on the extracted features to decode the reported perception on a single-trial basis. We apply the proposed approach to the multichannel intracortical LFP data collected from the middle temporal (MT) visual cortex in a macaque monkey performing an SFM task. We demonstrate that our approach is effective in extracting the discriminative features of the percept-related activity from LFP and achieves excellent decoding performance. We also find that the enhanced gamma band synchronization and reduced alpha and beta band desynchronization may be the underpinnings of the percept-related activity. PMID:19362902

  19. Local and global contributions to hemodynamic activity in mouse cortex.

    PubMed

    Pisauro, M Andrea; Benucci, Andrea; Carandini, Matteo

    2016-06-01

    Imaging techniques such as functional magnetic resonance imaging seek to estimate neural signals in local brain regions through measurements of hemodynamic activity. However, hemodynamic activity is accompanied by large vascular fluctuations of unclear significance. To characterize these fluctuations and their impact on estimates of neural signals, we used optical imaging in visual cortex of awake mice. We found that hemodynamic activity can be expressed as the sum of two components, one local and one global. The local component reflected presumed neural signals driven by visual stimuli in the appropriate retinotopic region. The global component constituted large fluctuations shared by larger cortical regions, which extend beyond visual cortex. These fluctuations varied from trial to trial, but they did not constitute noise; they correlated with pupil diameter, suggesting that they reflect variations in arousal or alertness. Distinguishing local and global contributions to hemodynamic activity may help understand neurovascular coupling and interpret measurements of hemodynamic responses. PMID:26984421

  20. Local and global contributions to hemodynamic activity in mouse cortex

    PubMed Central

    Pisauro, M. Andrea; Benucci, Andrea

    2016-01-01

    Imaging techniques such as functional magnetic resonance imaging seek to estimate neural signals in local brain regions through measurements of hemodynamic activity. However, hemodynamic activity is accompanied by large vascular fluctuations of unclear significance. To characterize these fluctuations and their impact on estimates of neural signals, we used optical imaging in visual cortex of awake mice. We found that hemodynamic activity can be expressed as the sum of two components, one local and one global. The local component reflected presumed neural signals driven by visual stimuli in the appropriate retinotopic region. The global component constituted large fluctuations shared by larger cortical regions, which extend beyond visual cortex. These fluctuations varied from trial to trial, but they did not constitute noise; they correlated with pupil diameter, suggesting that they reflect variations in arousal or alertness. Distinguishing local and global contributions to hemodynamic activity may help understand neurovascular coupling and interpret measurements of hemodynamic responses. PMID:26984421

  1. Millisecond Coupling of Local Field Potentials to Synaptic Currents in the Awake Visual Cortex

    PubMed Central

    Haider, Bilal; Schulz, David P.A.; Häusser, Michael; Carandini, Matteo

    2016-01-01

    Summary The cortical local field potential (LFP) is a common measure of population activity, but its relationship to synaptic activity in individual neurons is not fully established. This relationship has been typically studied during anesthesia and is obscured by shared slow fluctuations. Here, we used patch-clamp recordings in visual cortex of anesthetized and awake mice to measure intracellular activity; we then applied a simple method to reveal its coupling to the simultaneously recorded LFP. LFP predicted membrane potential as accurately as synaptic currents, indicating a major role for synaptic currents in the relationship between cortical LFP and intracellular activity. During anesthesia, cortical LFP predicted excitation far better than inhibition; during wakefulness, it predicted them equally well, and visual stimulation further enhanced predictions of inhibition. These findings reveal a central role for synaptic currents, and especially inhibition, in the relationship between the subthreshold activity of individual neurons and the cortical LFP during wakefulness. PMID:27021173

  2. Encoding of natural sounds by variance of the cortical local field potential.

    PubMed

    Ding, Nai; Simon, Jonathan Z; Shamma, Shihab A; David, Stephen V

    2016-06-01

    Neural encoding of sensory stimuli is typically studied by averaging neural signals across repetitions of the same stimulus. However, recent work has suggested that the variance of neural activity across repeated trials can also depend on sensory inputs. Here we characterize how intertrial variance of the local field potential (LFP) in primary auditory cortex of awake ferrets is affected by continuous natural sound stimuli. We find that natural sounds often suppress the intertrial variance of low-frequency LFP (<16 Hz). However, the amount of the variance reduction is not significantly correlated with the amplitude of the mean response at the same recording site. Moreover, the variance changes occur with longer latency than the mean response. Although the dynamics of the mean response and intertrial variance differ, spectro-temporal receptive field analysis reveals that changes in LFP variance have frequency tuning similar to multiunit activity at the same recording site, suggesting a local origin for changes in LFP variance. In summary, the spectral tuning of LFP intertrial variance and the absence of a correlation with the amplitude of the mean evoked LFP suggest substantial heterogeneity in the interaction between spontaneous and stimulus-driven activity across local neural populations in auditory cortex. PMID:26912594

  3. Extraction of percept-related induced local field potential during spontaneously reversing perception.

    PubMed

    Wang, Zhisong; Logothetis, Nikos K; Liang, Hualou

    2009-01-01

    The question of how perception arises from neuronal activity in the visual cortex is of fundamental importance in cognitive neuroscience. To address this question, we adopt a unique experimental paradigm in which bistable structure-from-motion (SFM) stimuli are employed to dissociate the visual input from perception while monitoring the cortical neural activity called local field potential (LFP). Consequently, the stimulus-evoked activity of LFP is not related to perception but the oscillatory induced activity of LFP may be percept-related. In this paper we focus on extracting the percept-related features of the induced activity from LFP in a monkey's visual cortex for decoding its bistable structure-from-motion perception. We first estimate the stimulus-evoked activity via a wavelet-based method and remove it from the single-trial LFP. We then use the common spatial patterns (CSP) approach to design spatial filters to extract the percept-related features from the remaining induced activity. We exploit the linear discriminant analysis (LDA) classifier on the extracted features to decode the reported perception on a single-trial basis. We demonstrate that our approach has excellent performance in estimating the stimulus-evoked activity, outperforming the Wiener filter, least mean square (LMS), and a local regression method called the locally weighted scatterplot smoothing (LOWESS), and that our approach is effective in extracting the discriminative features of the percept-related induced activity from LFP, which leads to excellent decoding performance. We also discover that the enhanced gamma band synchronization and reduced alpha band desynchronization may be the underpinnings of the induced activity. PMID:19608383

  4. Cosmological perturbations in SFT inspired non-local scalar field models

    NASA Astrophysics Data System (ADS)

    Koshelev, Alexey S.; Vernov, Sergey Yu.

    2012-10-01

    We study cosmological perturbations in models with a single non-local scalar field originating from the string field theory description of the rolling tachyon dynamics. We construct the equation for the energy density perturbations of the non-local scalar field and explicitly prove that for the free field it is identical to a system of local cosmological perturbation equations in a particular model with multiple (maybe infinitely many) local free scalar fields. We also show that vector and tensor perturbations are absent in this set-up.

  5. Conditions of activity bubble uniqueness in dynamic neural fields.

    PubMed

    Mikhailova, Inna; Goerick, Christian

    2005-02-01

    Dynamic neural fields (DNFs) offer a rich spectrum of dynamic properties like hysteresis, spatiotemporal information integration, and coexistence of multiple attractors. These properties make DNFs more and more popular in implementations of sensorimotor loops for autonomous systems. Applications often imply that DNFs should have only one compact region of firing neurons (activity bubble), whereas the rest of the field should not fire (e.g., if the field represents motor commands). In this article we prove the conditions of activity bubble uniqueness in the case of locally symmetric input bubbles. The qualitative condition on inhomogeneous inputs used in earlier work on DNFs is transfered to a quantitative condition of a balance between the internal dynamics and the input. The mathematical analysis is carried out for the two-dimensional case with methods that can be extended to more than two dimensions. The article concludes with an example of how our theoretical results facilitate the practical use of DNFs. PMID:15685393

  6. Spin noise explores local magnetic fields in a semiconductor.

    PubMed

    Ryzhov, Ivan I; Kozlov, Gleb G; Smirnov, Dmitrii S; Glazov, Mikhail M; Efimov, Yurii P; Eliseev, Sergei A; Lovtcius, Viacheslav A; Petrov, Vladimir V; Kavokin, Kirill V; Kavokin, Alexey V; Zapasskii, Valerii S

    2016-01-01

    Rapid development of spin noise spectroscopy of the last decade has led to a number of remarkable achievements in the fields of both magnetic resonance and optical spectroscopy. In this report, we demonstrate a new - magnetometric - potential of the spin noise spectroscopy and use it to study magnetic fields acting upon electron spin-system of an n-GaAs layer in a high-Q microcavity probed by elliptically polarized light. Along with the external magnetic field, applied to the sample, the spin noise spectrum revealed the Overhauser field created by optically oriented nuclei and an additional, previously unobserved, field arising in the presence of circularly polarized light. This "optical field" is directed along the light propagation axis, with its sign determined by sign of the light helicity. We show that this field results from the optical Stark effect in the field of the elliptically polarized light. This conclusion is supported by theoretical estimates. PMID:26882994

  7. The lure of local SETI: Fifty years of field experiments

    NASA Astrophysics Data System (ADS)

    Ailleris, Philippe

    2011-01-01

    With the commemoration in October 2007 of the Sputnik launch, space exploration celebrated its 50th anniversary. Despite impressive technological and scientific achievements the fascination for space has weakened during the last decades. One contributing factor has been the gradual disappearance of mankind's hope of discovering extraterrestrial life within its close neighbourhood. In striking contrast and since the middle of the 20th century, a non-negligible proportion of the population have already concluded that intelligent beings from other worlds do exist and visit Earth through space vehicles popularly called Unidentified Flying Objects (UFOs). In light of the continuous public interest for the UFO enigma symbolized by the recent widely diffused media announcements on the release of French and English governmental files; and considering the approach of broadening the strategies of the "Active SETI" approach and the existence of a rich multi-disciplinary UFO documentation of potential interest for SETI; this paper describes some past scientific attempts to demonstrate the physical reality of the phenomena and potentially the presence on Earth of probes of extraterrestrial origin. Details of the different instrumented field studies deployed by scientists and organizations during the period 1950-1990 in the USA, Canada and Europe are provided. In conclusion it will be argued that while continuing the current radio/optical SETI searches, there is the necessity to maintain sustaining attention to the topic of anomalous aerospace phenomena and to develop new rigorous research approaches.

  8. Quantum theory for plasmon-assisted local field enhancement

    NASA Astrophysics Data System (ADS)

    Grigorenko, Ilya

    2016-01-01

    We applied quantum theory for nonlocal response and plasmon-assisted field enhancement near a small metallic nanoscale antenna in the limit of weak incoming fields. A simple asymmetric bio-inspired design of the nanoantenna for polarization-resolved measurement is proposed. The spatial field intensity distribution was calculated for different field frequencies and polarizations. We have shown that the proposed design the antenna allows us to resolve the polarization of incoming photons.

  9. Quantum theory for plasmon-assisted local field enhancement

    NASA Astrophysics Data System (ADS)

    Grigorenko, Ilya

    We applied quantum theory for nonlocal response and plasmon-assisted field enhancement near a small metallic nanoscale antenna in the limit of weak incoming fields. A simple asymmetric bio-inspired design of the nanoantenna for polarization-resolved measurement is proposed. The spatial field intensity distribution was calculated for different field frequencies and polarizations. We have shown that the proposed design the antenna allows us to resolve the polarization of incoming photons.

  10. Local Activity Principle:. the Cause of Complexity and Symmetry Breaking

    NASA Astrophysics Data System (ADS)

    Mainzer, Klaus

    2013-01-01

    The principle of local activity is precisely the missing concept to explain the emergence of complex patterns in a homogeneous medium. Leon O. Chua discovered and defined this principle in the theory of nonlinear electronic circuits in a mathematically rigorous way. The local principle can be generalized and proven at least for the class of nonlinear reaction-diffusion systems in physics, chemistry, biology and brain research. Recently, it was realized by memristors for nanoelectronic device applications in technical brains. In general, the emergence of complex patterns and structures is explained by symmetry breaking in homogeneous media. The principle of local activity is the cause of symmetry breaking in homogeneous media. We argue that the principle of local activity is really fundamental in science and can even be identified in quantum cosmology as symmetry breaking of local gauge symmetries generating the complexity of matter and forces in our universe. Finally, we consider applications in economic, financial, and social systems with the emergence of equilibrium states, symmetry breaking at critical points of phase transitions and risky acting at the edge of chaos. In any case, the driving causes of symmetry breaking and the emergence of complexity are locally active elements, cells, units, or agents.

  11. Spin noise explores local magnetic fields in a semiconductor

    NASA Astrophysics Data System (ADS)

    Ryzhov, Ivan I.; Kozlov, Gleb G.; Smirnov, Dmitrii S.; Glazov, Mikhail M.; Efimov, Yurii P.; Eliseev, Sergei A.; Lovtcius, Viacheslav A.; Petrov, Vladimir V.; Kavokin, Kirill V.; Kavokin, Alexey V.; Zapasskii, Valerii S.

    2016-02-01

    Rapid development of spin noise spectroscopy of the last decade has led to a number of remarkable achievements in the fields of both magnetic resonance and optical spectroscopy. In this report, we demonstrate a new - magnetometric - potential of the spin noise spectroscopy and use it to study magnetic fields acting upon electron spin-system of an n-GaAs layer in a high-Q microcavity probed by elliptically polarized light. Along with the external magnetic field, applied to the sample, the spin noise spectrum revealed the Overhauser field created by optically oriented nuclei and an additional, previously unobserved, field arising in the presence of circularly polarized light. This “optical field” is directed along the light propagation axis, with its sign determined by sign of the light helicity. We show that this field results from the optical Stark effect in the field of the elliptically polarized light. This conclusion is supported by theoretical estimates.

  12. Spin noise explores local magnetic fields in a semiconductor

    PubMed Central

    Ryzhov, Ivan I.; Kozlov, Gleb G.; Smirnov, Dmitrii S.; Glazov, Mikhail M.; Efimov, Yurii P.; Eliseev, Sergei A.; Lovtcius, Viacheslav A.; Petrov, Vladimir V.; Kavokin, Kirill V.; Kavokin, Alexey V.; Zapasskii, Valerii S.

    2016-01-01

    Rapid development of spin noise spectroscopy of the last decade has led to a number of remarkable achievements in the fields of both magnetic resonance and optical spectroscopy. In this report, we demonstrate a new – magnetometric – potential of the spin noise spectroscopy and use it to study magnetic fields acting upon electron spin-system of an n-GaAs layer in a high-Q microcavity probed by elliptically polarized light. Along with the external magnetic field, applied to the sample, the spin noise spectrum revealed the Overhauser field created by optically oriented nuclei and an additional, previously unobserved, field arising in the presence of circularly polarized light. This “optical field” is directed along the light propagation axis, with its sign determined by sign of the light helicity. We show that this field results from the optical Stark effect in the field of the elliptically polarized light. This conclusion is supported by theoretical estimates. PMID:26882994

  13. Local excitations of a spin glass in a magnetic field

    NASA Astrophysics Data System (ADS)

    Lamarcq, J.; Bouchaud, J.-P.; Martin, O. C.

    2003-07-01

    We study the minimum energy clusters (MEC) above the ground state for the 3-d Edwards-Anderson Ising spin glass in a magnetic field. For fields B below 0.4, we find that the field has almost no effect on the excitations that we can probe, of volume V⩽64. As found previously for B=0, their energies decrease with V, and their magnetization remains very small (even slightly negative). For larger fields, both the MEC energy and magnetization grow with V, as expected in a paramagnetic phase. However, all results appear to scale as BV (instead of B(V) as expected from droplet arguments), suggesting that the spin glass phase is destroyed by any small field. Finally, the geometry of the MEC is completely insensitive to the field, giving further credence that they are lattice animals, in the presence or the absence of a field.

  14. Holocene eolian activity in the Minot dune field, North Dakota

    USGS Publications Warehouse

    Muhs, D.R.; Stafford, Thomas W., Jr.; Been, J.; Mahan, S.A.; Burdett, J.; Skipp, G.; Rowland, Z.M.

    1997-01-01

    Stabilized eolian sand is common over much of the Great Plains region of the United States and Canada, including a subhumid area of ??? 1500 km2 near Minot, North Dakota. Eolian landforms consist of sand sheets and northwest-trending parabolic dunes. Dunes and sand sheets in the Minot field are presently stabilized by a cover of prairie grasses or oak woodland. Stratigraphic studies and accelerator mass spectrometry radiocarbon dating of paleosols indicate at least two periods of eolian sand movement in the late Holocene. Pedologic data suggest that all of the dune field has experienced late Holocene dune activity, though not all parts of the dune field may have been active simultaneously. Similar immobile element (Ti, Zr, La, Ce) concentrations support the interpretation that eolian sands are derived from local glaciofluvial and glaciolacustrine sediments. However, glaciolacustrine and glaciofluvial source sediments have high Ca concentrations from carbonate minerals, whereas dune sands are depleted in Ca. Because noneolian-derived soils in the area are calcareous, these data indicate that the Minot dune field may have had extended periods of activity in the Holocene, such that eolian abrasion removed soft carbonate minerals. The southwest-facing parts of some presently stabilized dunes were active during the 1930s drought, but were revegetated during the wetter years of the 1940s. These observations indicate that severe droughts accompanied by high temperatures are the most likely cause of Holocene eolian activity.

  15. Connecting Local Yield Stresses with Plastic Activity in Amorphous Solids

    NASA Astrophysics Data System (ADS)

    Patinet, Sylvain; Vandembroucq, Damien; Falk, Michael L.

    2016-07-01

    In model amorphous solids produced via differing quench protocols, a strong correlation is established between local yield stress measured by direct local probing of shear stress thresholds and the plastic rearrangements observed during remote loading in shear. This purely local measure shows a higher predictive power for identifying sites of plastic activity when compared with more conventional structural properties. Most importantly, the sites of low local yield stress, thus defined, are shown to be persistent, remaining predictive of deformation events even after fifty or more such plastic rearrangements. This direct and nonperturbative approach gives access to relevant transition pathways that control the stability of amorphous solids. Our results reinforce the relevance of modeling plasticity in amorphous solids based on a gradually evolving population of discrete and local zones preexisting in the structure.

  16. Tip-enhanced Raman nanographs: mapping topography and local electric fields.

    PubMed

    El-Khoury, Patrick Z; Gong, Yu; Abellan, Patricia; Arey, Bruce W; Joly, Alan G; Hu, Dehong; Evans, James E; Browning, Nigel D; Hess, Wayne P

    2015-04-01

    We report tip-enhanced Raman imaging experiments in which information on sample topography and local electric fields is simultaneously obtained using an all-optical detection scheme. We demonstrate how a Raman-active 4,4'-dimercaptostilbene (DMS)-coated gold tip of an atomic force microscope can be used to simultaneously map the topography and image the electric fields localized at nanometric (20 and 5 nm wide) slits lithographically etched in silver, all using optical signals. Bimodal imaging is feasible by virtue of the frequency-resolved optical response of the functionalized metal probe. Namely, the probe position-dependent signals can be subdivided into two components. The first is a 500-2250 cm(-1) Raman-shifted signal, characteristic of the tip-bound DMS molecules. The molecules report on topography through the intensity contrast observed as the tip scans across the nanoscale features. The variation in molecular Raman activity arises from the absence/formation of a plasmonic junction between the scanning probe and patterned silver surface, which translates into dimmed/enhanced Raman signatures of DMS. Using these molecular signals, we demonstrate that sub-15 nm spatial resolution is attainable using a 30 nm DMS-coated gold tip. The second response consists of two correlated sub-500 cm(-1) signals arising from mirror-like reflections of (i) the incident laser field and (ii) the Raman scattered response of an underlying glass support (at 100-500 cm(-1)) off the gold tip. We show that both the reflected low-wavenumber signals trace the local electric fields in the vicinity of the nanometric slits. PMID:25741776

  17. Oxindole-3-spiropyrrolidines and -piperidines. Synthesis and local anesthetic activity.

    PubMed

    Kornet, M J; Thio, A P

    1976-07-01

    The synthesis and local anesthetic properties of five 1-dealkyloxindole-3-spiropyrrolidines and six 1-dealkyloxindole-3-spiropiperidines are described. The compounds studied include members of all five possible positional isomers of the two classes of spirooxindoles; all showed local anesthetic activity by the rat sciatic nerve block method. The coincidence of the least variability in the relative positions of basic nitrogen, amide carbonyl, and aromatic ring (compounds 1 and 6) with lowest normalized toxicity is noteworthy. PMID:940109

  18. Mesoscopic turbulence and local order in Janus particles self-propelling under an ac electric field

    NASA Astrophysics Data System (ADS)

    Nishiguchi, Daiki; Sano, Masaki

    2015-11-01

    To elucidate mechanisms of mesoscopic turbulence exhibited by active particles, we experimentally study turbulent states of nonliving self-propelled particles. We realize an experimental system with dense suspensions of asymmetrical colloidal particles (Janus particles) self-propelling on a two-dimensional surface under an ac electric field. Velocity fields of the Janus particles in the crowded situation can be regarded as a sort of turbulence because it contains many vortices and their velocities change abruptly. Correlation functions of their velocity field reveal the coexistence of polar alignment and antiparallel alignment interactions, which is considered to trigger mesoscopic turbulence. Probability distributions of local order parameters for polar and nematic orders indicate the formation of local clusters with particles moving in the same direction. A broad peak in the energy spectrum of the velocity field appears at the spatial scales where the polar alignment and the cluster formation are observed. Energy is injected at the particle scale and conserved quantities such as energy could be cascading toward the larger clusters.

  19. Mesoscopic turbulence and local order in Janus particles self-propelling under an ac electric field.

    PubMed

    Nishiguchi, Daiki; Sano, Masaki

    2015-11-01

    To elucidate mechanisms of mesoscopic turbulence exhibited by active particles, we experimentally study turbulent states of nonliving self-propelled particles. We realize an experimental system with dense suspensions of asymmetrical colloidal particles (Janus particles) self-propelling on a two-dimensional surface under an ac electric field. Velocity fields of the Janus particles in the crowded situation can be regarded as a sort of turbulence because it contains many vortices and their velocities change abruptly. Correlation functions of their velocity field reveal the coexistence of polar alignment and antiparallel alignment interactions, which is considered to trigger mesoscopic turbulence. Probability distributions of local order parameters for polar and nematic orders indicate the formation of local clusters with particles moving in the same direction. A broad peak in the energy spectrum of the velocity field appears at the spatial scales where the polar alignment and the cluster formation are observed. Energy is injected at the particle scale and conserved quantities such as energy could be cascading toward the larger clusters. PMID:26651697

  20. Optical Detection of Local Electric Field Dynamics in Solutions by Waveguide-integrated Graphene Device

    NASA Astrophysics Data System (ADS)

    Horng, Jason; Balch, Halleh; Feng Wang Team

    The spatio-temporal dynamics of local electric fields in ionic solutions plays a central role in various chemical and biological processes ranging from batteries technologies to neuron signaling. A non-invasive, precise detection scheme for measuring local electric fields dynamics has long been sought for. Here, we report a sensitive, high-speed, high spatial resolution optical imaging method for local electric fields based on the unique optoelectronic properties of graphene. With enhancement from a waveguide involving critical coupling concept, we show that our graphene optical sensor provides an ideal platform for studying dynamics of local electric field fluctuations in different nonequilibrium solutions.

  1. Local flux intrusion in HTS annuli during pulsed field magnetization

    NASA Astrophysics Data System (ADS)

    Korotkov, V. S.; Krasnoperov, E. P.; Kartamyshev, A. A.

    2016-03-01

    During pulsed field magnetization of melt-grown HTS flux jumps can occur and the shielding current falls by 10-20 times. As the duration of pulse is shorter than the temperature relaxation time (<< 1 s), the circular current remains small during the field falling. The residual trapped field in the hole of the annulus has a direction opposite to that of the pulsed field. Small circular current and high critical current density are explained by the fact that flux moves through narrow regions of the annulus body. The angle of the sector with “soft flux” (i.e. a low Jc region) is estimated to be ∼ 7 deg.

  2. Stimulus selectivity and spatial coherence of gamma components of the local field potential

    PubMed Central

    Jia, Xiaoxuan; Smith, Matthew A.; Kohn, Adam

    2011-01-01

    The gamma frequencies of the local field potential (LFP) provide a physiological correlate for numerous perceptual and cognitive phenomena and have been proposed to play a role in cortical function. Understanding the spatial extent of gamma and its relationship to spiking activity is critical for interpreting this signal and elucidating its function, but previous studies have provided widely disparate views of these properties. We addressed these issues by simultaneously recording LFPs and spiking activity using microelectrode arrays implanted in the primary visual cortex of macaque monkeys. We find that the spatial extent of gamma and its relationship to local spiking activity is stimulus dependent. Small gratings, and those masked with noise, induce a broadband increase in spectral power. This signal is tuned similarly to spiking activity and has limited spatial coherence. Large gratings, on the other hand, induce a gamma rhythm characterized by a distinctive spectral “bump”, which is coherent across widely separated sites. This signal is well tuned, but its stimulus preference is similar across millimeters of cortex. The preference of this global gamma rhythm is sensitive to adaptation, in a manner consistent with it magnifying a bias in the neuronal representation of visual stimuli. Gamma thus arises from two sources that reflect different spatial scales of neural ensemble activity. Our results show that there is not a single, fixed ensemble contributing to gamma and that the selectivity of gamma cannot be used to infer its spatial extent. PMID:21697389

  3. ABRUPT LONGITUDINAL MAGNETIC FIELD CHANGES IN FLARING ACTIVE REGIONS

    SciTech Connect

    Petrie, G. J. D.; Sudol, J. J.

    2010-12-01

    We characterize the changes in the longitudinal photospheric magnetic field during 38 X-class and 39 M-class flares within 65{sup 0} of disk center using 1 minute GONG magnetograms. In all 77 cases, we identify at least one site in the flaring active region where clear, permanent, stepwise field changes occurred. The median duration of the field changes was about 15 minutes and was approximately equal for X-class and for M-class flares. The absolute values of the field changes ranged from the detection limit of {approx}10 G to as high as {approx}450 G in two exceptional cases. The median value was 69 G. Field changes were significantly stronger for X-class than for M-class flares and for limb flares than for disk-center flares. Longitudinal field changes less than 100 G tended to decrease longitudinal field strengths, both close to disk center and close to the limb, while field changes greater than 100 G showed no such pattern. Likewise, longitudinal flux strengths tended to decrease during flares. Flux changes, particularly net flux changes near disk center, correlated better than local field changes with GOES peak X-ray flux. The strongest longitudinal field and flux changes occurred in flares observed close to the limb. We estimate the change of Lorentz force associated with each flare and find that this is large enough in some cases to power seismic waves. We find that longitudinal field decreases would likely outnumber increases at all parts of the solar disk within 65{sup 0} of disk center, as in our observations, if photospheric field tilts increase during flares as predicted by Hudson et al.

  4. Sub-10 nm near-field localization by plasmonic metal nanoaperture arrays with ultrashort light pulses

    PubMed Central

    Lee, Hongki; Kim, Chulhong; Kim, Donghyun

    2015-01-01

    Near-field localization by ultrashort femtosecond light pulses has been investigated using simple geometrical nanoapertures. The apertures employ circular, rhombic, and triangular shapes to localize the distribution of surface plasmon. To understand the geometrical effect on the localization, aperture length and period of the nanoapertures were varied. Aperture length was shown to affect the performance more than aperture period due mainly to intra-aperture coupling of near-fields. Triangular apertures provided the strongest spatial localization below 10 nm in size as well as the highest enhancement of field intensity by more than 7000 times compared to the incident light pulse. Use of ultrashort pulses was found to allow much stronger light localization than with continuous-wave light. The results can be used for super-localization sensing and imaging applications where spatially localized fields can break through the limits in achieving improved sensitivity and resolution. PMID:26628326

  5. Sub-10 nm near-field localization by plasmonic metal nanoaperture arrays with ultrashort light pulses.

    PubMed

    Lee, Hongki; Kim, Chulhong; Kim, Donghyun

    2015-01-01

    Near-field localization by ultrashort femtosecond light pulses has been investigated using simple geometrical nanoapertures. The apertures employ circular, rhombic, and triangular shapes to localize the distribution of surface plasmon. To understand the geometrical effect on the localization, aperture length and period of the nanoapertures were varied. Aperture length was shown to affect the performance more than aperture period due mainly to intra-aperture coupling of near-fields. Triangular apertures provided the strongest spatial localization below 10 nm in size as well as the highest enhancement of field intensity by more than 7000 times compared to the incident light pulse. Use of ultrashort pulses was found to allow much stronger light localization than with continuous-wave light. The results can be used for super-localization sensing and imaging applications where spatially localized fields can break through the limits in achieving improved sensitivity and resolution. PMID:26628326

  6. Localization from near-source quasi-static electromagnetic fields

    SciTech Connect

    Mosher, J.C.

    1993-09-01

    A wide range of research has been published on the problem of estimating the parameters of electromagnetic and acoustical sources from measurements of signals measured at an array of sensors. In the quasi-static electromagnetic cases examined here, the signal variation from a point source is relatively slow with respect to the signal propagation and the spacing of the array of sensors. As such, the location of the point sources can only be determined from the spatial diversity of the received signal across the array. The inverse source localization problem is complicated by unknown model order and strong local minima. The nonlinear optimization problem is posed for solving for the parameters of the quasi-static source model. The transient nature of the sources can be exploited to allow subspace approaches to separate out the signal portion of the spatial correlation matrix. Decomposition techniques are examined for improved processing, and an adaptation of MUtiple SIgnal Characterization (MUSIC) is presented for solving the source localization problem. Recent results on calculating the Cramer-Rao error lower bounds are extended to the multidimensional problem here. This thesis focuses on the problem of source localization in magnetoencephalography (MEG), with a secondary application to thunderstorm source localization. Comparisons are also made between MEG and its electrical equivalent, electroencephalography (EEG). The error lower bounds are examined in detail for several MEG and EEG configurations, as well as localizing thunderstorm cells over Cape Canaveral and Kennedy Space Center. Time-eigenspectrum is introduced as a parsing technique for improving the performance of the optimization problem.

  7. Frequency-dependent local field factors in dielectric liquids by a polarizable force field and molecular dynamics simulations

    SciTech Connect

    Davari, Nazanin; Haghdani, Shokouh; Åstrand, Per-Olof

    2015-12-31

    A force field model for calculating local field factors, i.e. the linear response of the local electric field for example at a nucleus in a molecule with respect to an applied electric field, is discussed. It is based on a combined charge-transfer and point-dipole interaction model for the polarizability, and thereby it includes two physically distinct terms for describing electronic polarization: changes in atomic charges arising from transfer of charge between the atoms and atomic induced dipole moments. A time dependence is included both for the atomic charges and the atomic dipole moments and if they are assumed to oscillate with the same frequency as the applied electric field, a model for frequency-dependent properties are obtained. Furthermore, if a life-time of excited states are included, a model for the complex frequency-dependent polariability is obtained including also information about excited states and the absorption spectrum. We thus present a model for the frequency-dependent local field factors through the first molecular excitation energy. It is combined with molecular dynamics simulations of liquids where a large set of configurations are sampled and for which local field factors are calculated. We are normally not interested in the average of the local field factor but rather in configurations where it is as high as possible. In electrical insulation, we would like to avoid high local field factors to reduce the risk for electrical breakdown, whereas for example in surface-enhanced Raman spectroscopy, high local field factors are desired to give dramatically increased intensities.

  8. Frequency-dependent local field factors in dielectric liquids by a polarizable force field and molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Davari, Nazanin; Haghdani, Shokouh; Åstrand, Per-Olof

    2015-12-01

    A force field model for calculating local field factors, i.e. the linear response of the local electric field for example at a nucleus in a molecule with respect to an applied electric field, is discussed. It is based on a combined charge-transfer and point-dipole interaction model for the polarizability, and thereby it includes two physically distinct terms for describing electronic polarization: changes in atomic charges arising from transfer of charge between the atoms and atomic induced dipole moments. A time dependence is included both for the atomic charges and the atomic dipole moments and if they are assumed to oscillate with the same frequency as the applied electric field, a model for frequency-dependent properties are obtained. Furthermore, if a life-time of excited states are included, a model for the complex frequency-dependent polariability is obtained including also information about excited states and the absorption spectrum. We thus present a model for the frequency-dependent local field factors through the first molecular excitation energy. It is combined with molecular dynamics simulations of liquids where a large set of configurations are sampled and for which local field factors are calculated. We are normally not interested in the average of the local field factor but rather in configurations where it is as high as possible. In electrical insulation, we would like to avoid high local field factors to reduce the risk for electrical breakdown, whereas for example in surface-enhanced Raman spectroscopy, high local field factors are desired to give dramatically increased intensities.

  9. Geometrical parameters effects on local electric field enhancement of silver-dielectric-silver multilayer nanoshell

    SciTech Connect

    Shirzaditabar, Farzad; Saliminasab, Maryam

    2013-05-15

    The local electric field enhancement at different points of silver-dielectric-silver nanoshell is investigated using quasi-static theory. Because of the symmetric and anti-symmetric coupling between surface plasmon of inner silver core and outer silver shell, the local electric field spectrum of silver-dielectric-silver has two distinct peaks at resonance wavelengths. The silver core size and middle dielectric thickness affect the local electric field enhancement at different points of silver-dielectric-silver nanoshell. Increasing the silver core radius always leads to blue shift of shorter resonance wavelength and red shift of longer resonance wavelength. We observed two distinct local electric field peaks, which are corresponded to the symmetric and anti-symmetric coupling between inner and outer surface plasmons. In a system with thick silver shell, local electric field enhancement is greater than a system with thin silver shell. However, the local electric field variations as a function of silver core radius in both systems are different at different points of nanoshell. The effects of the dielectric thickness variations on local electric field are different from those from silver core size variations. As the dielectric thickness is about 3 nm, the highest local electric field enhancement occurs at the surface of the inner silver core, where the symmetric and anti-symmetric modes are mixed together.

  10. Geometrical parameters effects on local electric field enhancement of silver-dielectric-silver multilayer nanoshell

    NASA Astrophysics Data System (ADS)

    Shirzaditabar, Farzad; Saliminasab, Maryam

    2013-05-01

    The local electric field enhancement at different points of silver-dielectric-silver nanoshell is investigated using quasi-static theory. Because of the symmetric and anti-symmetric coupling between surface plasmon of inner silver core and outer silver shell, the local electric field spectrum of silver-dielectric-silver has two distinct peaks at resonance wavelengths. The silver core size and middle dielectric thickness affect the local electric field enhancement at different points of silver-dielectric-silver nanoshell. Increasing the silver core radius always leads to blue shift of shorter resonance wavelength and red shift of longer resonance wavelength. We observed two distinct local electric field peaks, which are corresponded to the symmetric and anti-symmetric coupling between inner and outer surface plasmons. In a system with thick silver shell, local electric field enhancement is greater than a system with thin silver shell. However, the local electric field variations as a function of silver core radius in both systems are different at different points of nanoshell. The effects of the dielectric thickness variations on local electric field are different from those from silver core size variations. As the dielectric thickness is about 3 nm, the highest local electric field enhancement occurs at the surface of the inner silver core, where the symmetric and anti-symmetric modes are mixed together.

  11. Chapter A9. Safety in Field Activities

    USGS Publications Warehouse

    Lane, Susan L.; Ray, Ronald G.

    1998-01-01

    The National Field Manual for the Collection of Water-Quality Data (National Field Manual) describes protocols (requirements and recommendations) and provides guidelines for U.S. Geological Survey (USGS) personnel who collect data used to assess the quality of the Nation's surface-water and ground-water resources. This chapter of the manual addresses topics related to personal safety to be used in the collection of water-quality data, including: policies and general regulations on field safety; transportation of people and equipment; implementation of surface-water and ground-water activities; procedures for handling chemicals; and information on potentially hazardous environmental conditions, animals, and plants. Each chapter of the National Field Manual is published separately and revised periodically. Newly published and revised chapters will be announced on the USGS Home Page on the World Wide Web under 'New Publications of the U.S. Geological Survey.' The URL for this page is http://pubs.usgs.gov/publications/ index.html.

  12. Atom localization in a Doppler broadened medium via two standing-wave fields

    NASA Astrophysics Data System (ADS)

    Abd-Elnabi, Somia; Osman, Kariman I.

    2016-01-01

    The atom localization has been achieved in a four-level V-type atomic system interacting with two classical unidirectional standing-wave fields and weak probe field in a Doppler broadened medium under several conditions at very low temperature. The precision of the atom localization is compared with the system in the presence and absence of the Doppler broadened medium. The influence of some parameters such as the amplitude, wave vectors and the phase shift of the standing-wave fields on the atom localization is studied and has been found to obtain various atom localization patterns with symmetric shape.

  13. Regional and local geologic structure of the Momotombo field, Nicaragua

    SciTech Connect

    Goldsmith, L.H.

    1980-09-01

    The regional geologic-tectonic setting of northwestern Nicaragua is the result of subduction. Differential plate margin movement and segmentation formed a deep rift paralleling the Middle American Trench. Deep-seated shear faults provided access to sublithospheric magmas to create the Nicaraguan volcanic chain. Volcan Momotombo is the southernmost volcano of the Marabios Range of northern Nicaragua. It hosts a proven geothermal resource known as the Momotombo field, located within a small graben structure and measuring less than one square kilometer. This geothermally productive area appears not to be a geothermal reservoir, but rather part of a thermal convection system. Wells in the central and eastern part of the field have diminished in output and temperature. The presence of a temperature inversion zone, clearly distinguishable in the eastern end of the field, indicates that no conductive heating of the productive zone is taking place.

  14. A Hi Fidelity Asymptotic Theory For Local Field Recovery Inside Pre-stressed Composite Media

    SciTech Connect

    Breitzman, Timothy; Lipton, Robert; Iarve, Endel

    2008-02-15

    We introduce a new mathematically rigorous high fidelity asymptotic theory for recovering the local field behavior inside complex composite architectures. The theory applies to zones containing strong spatial variance of local material properties. The method is used to recover the local field across ply interfaces for a pre-stressed multi-ply fiber reinforced composite. The results are shown to be in good agreement with direct numerical simulations for realistic fiber sizes and fiber-matrix elastic properties.

  15. Spontaneous Activity Drives Local Synaptic Plasticity In Vivo.

    PubMed

    Winnubst, Johan; Cheyne, Juliette E; Niculescu, Dragos; Lohmann, Christian

    2015-07-15

    Spontaneous activity fine-tunes neuronal connections in the developing brain. To explore the underlying synaptic plasticity mechanisms, we monitored naturally occurring changes in spontaneous activity at individual synapses with whole-cell patch-clamp recordings and simultaneous calcium imaging in the mouse visual cortex in vivo. Analyzing activity changes across large populations of synapses revealed a simple and efficient local plasticity rule: synapses that exhibit low synchronicity with nearby neighbors (<12 μm) become depressed in their transmission frequency. Asynchronous electrical stimulation of individual synapses in hippocampal slices showed that this is due to a decrease in synaptic transmission efficiency. Accordingly, experimentally increasing local synchronicity, by stimulating synapses in response to spontaneous activity at neighboring synapses, stabilized synaptic transmission. Finally, blockade of the high-affinity proBDNF receptor p75(NTR) prevented the depression of asynchronously stimulated synapses. Thus, spontaneous activity drives local synaptic plasticity at individual synapses in an "out-of-sync, lose-your-link" fashion through proBDNF/p75(NTR) signaling to refine neuronal connectivity. VIDEO ABSTRACT. PMID:26182421

  16. Locality and entanglement in bandlimited quantum field theory

    NASA Astrophysics Data System (ADS)

    Pye, Jason; Donnelly, William; Kempf, Achim

    2015-11-01

    We consider a model for a Planck-scale ultraviolet cutoff which is based on Shannon sampling. Shannon sampling originated in information theory, where it expresses the equivalence of continuous and discrete representations of information. When applied to quantum field theory, Shannon sampling expresses a hard ultraviolet cutoff in the form of a bandlimitation. This introduces nonlocality at the cutoff scale in a way that is more subtle than a simple discretization of space: quantum fields can then be represented as either living on continuous space or, entirely equivalently, as living on any one lattice whose average spacing is sufficiently small. We explicitly calculate vacuum entanglement entropies in 1 +1 dimensions and we find a transition between logarithmic and linear scaling of the entropy, which is the expected 1 +1 dimensional analog of the transition from an area to a volume law. We also use entanglement entropy and mutual information as measures to probe in detail the localizability of the field degrees of freedom. We find that, even though neither translation nor rotation invariance are broken, each field degree of freedom occupies an incompressible volume of space, indicating a finite information density.

  17. Locality and entanglement in bandlimited quantum field theory

    NASA Astrophysics Data System (ADS)

    Pye, Jason; Donnelly, William; Kempf, Achim

    We consider a model for a Planck scale ultraviolet cutoff which is based on Shannon sampling. Shannon sampling originated in information theory, where it expresses the equivalence of continuous and discrete representations of information. When applied to quantum field theory, Shannon sampling expresses a hard ultraviolet cutoff in the form of a bandlimitation. This introduces nonlocality at the cutoff scale in a way that is more subtle than a simple discretization of space: quantum fields can then be represented as either living on continuous space or, entirely equivalently, as living on any one lattice whose average spacing is sufficiently small. We explicitly calculate vacuum entanglement entropies in 1+1 dimensions and we find a transition between logarithmic and linear scaling of the entropy, which is the expected 1+1 dimensional analog of the transition from an area to a volume law. We also use entanglement entropy and mutual information as measures to probe in detail the localizability of the field degrees of freedom. We find that, even though neither translation nor rotation invariance are broken, each field degree of freedom occupies an incompressible volume of space, indicating a finite information density.

  18. Magnetic field associated with active electrochemical corrosion

    NASA Astrophysics Data System (ADS)

    Abedi, Afshin

    The purpose of this work is to provide a better understanding of the underlying sources of the magnetic field associated with ongoing electrochemical corrosion, to investigate the spatio-temporal information content of the corrosion magnetic field, and to evaluate its potential utility in non-invasive quantification of hidden corrosion. The importance of this work lies in the fact that conventional electrochemical instruments and techniques are not well suited for non-invasive measurements of the rate and dynamics of corrosion in occluded regions such as in aircraft lap joints. With the increase in the number of aging engineered systems there is an increasing demand for more accurate corrosion predictive models that can improve the probability of detection of corrosion induced flaws in structures, and hence reduce the risk of catastrophic failures. Therefore, such rate information is of great importance to the corrosion community. At the present time, there are no other techniques capable of providing such information. This work is the first successful attempt at quantification of the rate of corrosion through non- invasive measurements of its associated magnetic field. It includes the development of appropriate experimental techniques and associated models. Herein we have reviewed previous experiments, explored various exposure conditions and sample geometries, and discussed appropriate experimental procedures. We have defined quantitative magnetic parameters and, in conjunction with mass loss calibration measurements, have used them to determine non-invasively the rate and dynamics of ongoing hidden corrosion. We conclude that the corrosion magnetic field contains spatial and temporal information that correlate with the distribution, magnitude, and time course of currents associated with electrochemical corrosion. In conjunction with appropriate calibration experiments, sample geometry, and experimental topology, the magnetic activity of a corroding sample can be

  19. The triggering of local substorm activity by HF SURA heater

    NASA Astrophysics Data System (ADS)

    Ruzhin, Yuri; Parrot, Michel; Kovalev, Victor; Plastinin, Yuri; Kuznetsov, Vladimir; Vladimir Frolov, S.

    The results of analysis of helio-geophisical conditions of experiments 2007-2012 on local modification of ionosphere by powerful HF radio waves of SURA facility are presented. All experiment were conducted at sector of local time of Harang discontinuity for most probable influence of powerful HF pumping during the heater functioning on activation of natural processes at subauroral ionosphere - magnetosphere region. The peculiarity of these experiments was that all of these were executed with use of operative frequency, which was higher than upper hybrid frequency for background plasma of F2-layer maximum. It was obtained that, at least, in two experiments the observed substorm activity in zone northern SURA heater could be stimulated by its functionment.In the present study the ray tracing analysis clearly shows that ionosphere density decreasing (from DEMETER and IONEX data) at higher than SURA latitudes can redirect and refocused transmitter beam power in northward structure away from the beam center by refraction. By this way we have chance to participate by means of radiated SURA HF power in subauroral and auroral processes It is shown that results of groundbased, International Space Station and satellite DEMETER measurements as in vicinity a SURA location and in magnetic conjugated region support the conclusion (output) about reasons and possibility of substorm localization by action of SURA heater. The possible mechanisms of the local substorm activation are discussed.

  20. Equatorial longitude and local time variations of topside magnetic field-aligned ion drifts at solar minimum

    NASA Astrophysics Data System (ADS)

    Burrell, A. G.; Heelis, R. A.; Stoneback, R. A.

    2012-04-01

    In the topside ionosphere, the high mobility of the plasma along the magnetic field allows field-aligned ion drifts to occur readily as a result of field-aligned gravitational forces, collisional forces, or pressure gradients. Therefore, variations in the field-aligned ion drifts can be used to explore the influence of thermospheric, electrodynamic, and chemical processes on the ionosphere. Longitude and local time variations in the field-aligned ion drifts near the magnetic equator are presented using observations from the Coupled Ion Neutral Dynamics Investigation on board the Communications/Navigation Outage Forecast System satellite. These observations were obtained during the period of extremely low solar activity present in 2008 and 2009, allowing the seasonal, local time, and longitudinal variations to reveal the relative importance of the processes responsible for topside field-aligned plasma drifts during solar minimum. This investigation found that the low-altitude winds and tides, the net ionization or loss, and the meridional E×B drift were all influential in creating longitudinal and local time variations in the field-aligned drift, though the strength of the influence seen by each driver was found to vary with season, local time, and longitude.

  1. Tabu for matched-field source localization and geoacoustic inversion.

    PubMed

    Michalopoulou, Zoi-Heleni; Ghosh-Dastidar, Urmi

    2004-01-01

    Tabu is a global optimization technique that has been very successful in operations research. In this paper, a Tabu-based method is developed for source localization and geoacoustic inversion with underwater sound data; the method relies on memory to guide the multiparameter search. Tabu is evaluated through a comparison to simulating annealing. Both methods are tested by inverting synthetic data for various numbers of unknown parameters. Tabu is found to be superior to the simulated annealing variant implemented here in terms both of accuracy and efficiency. Inversion results from the SWellEX-96 data set are also presented. PMID:14759004

  2. Measuring Instantaneous Frequency of Local Field Potential Oscillations using the Kalman Smoother

    PubMed Central

    Nguyen, David P.; Wilson, Matthew A.; Brown, Emery N.; Barbieri, Riccardo

    2009-01-01

    Rhythmic local field potentials (LFP) arise from coordinated neural activity. Inference of neural function based on the properties of brain rhythms remains a challenging data analysis problem. Algorithms that characterize non-stationary rhythms with high temporal and spectral resolution may be useful for interpreting LFP activity on the timescales in which they are generated. We propose a Kalman smoother based dynamic autoregressive model for tracking the instantaneous frequency (iFreq) and frequency modulation (FM) of noisy and non-stationary sinusoids such as those found in LFP data. We verify the performance of our algorithm using simulated data with broad spectral content, and demonstrate its application using real data recorded from behavioral learning experiments. In analyses of ripple oscillations (100-250 Hz) recorded from the rodent hippocampus, our algorithm identified novel repetitive, short timescale frequency dynamics. Our results suggest that iFreq and FM may be useful measures for the quantification of small timescale LFP dynamics. PMID:19699763

  3. Fast and reliable identification of axons, axon initial segments and dendrites with local field potential recording

    PubMed Central

    Petersen, Anders V.; Johansen, Emil Ø.; Perrier, Jean-François

    2015-01-01

    The axon initial segment (AIS) is an essential neuronal compartment. It is usually where action potentials are initiated. Recent studies demonstrated that the AIS is a plastic structure that can be regulated by neuronal activity and by the activation of metabotropic receptors. Studying the AIS in live tissue can be difficult because its identification is not always reliable. Here we provide a new technique allowing a fast and reliable identification of the AIS in live brain slice preparations. By simultaneous recording of extracellular local field potentials and whole-cell patch-clamp recording of neurons, we can detect sinks caused by inward currents flowing across the membrane. We determine the location of the AIS by comparing the timing of these events with the action potential. We demonstrate that this method allows the unequivocal identification of the AIS of different types of neurons from the brain. PMID:26578887

  4. Real-time estimation and biofeedback of single-neuron firing rates using local field potentials

    PubMed Central

    Hall, Thomas M.; Nazarpour, Kianoush; Jackson, Andrew

    2014-01-01

    The long-term stability and low-frequency composition of local field potentials (LFPs) offer important advantages for robust and efficient neuroprostheses. However, cortical LFPs recorded by multi-electrode arrays are often assumed to contain only redundant information arising from the activity of large neuronal populations. Here we show that multichannel LFPs in monkey motor cortex each contain a slightly different mixture of distinctive slow potentials that accompany neuronal firing. As a result, the firing rates of individual neurons can be estimated with surprising accuracy. We implemented this method in a real-time biofeedback brain–machine interface, and found that monkeys could learn to modulate the activity of arbitrary neurons using feedback derived solely from LFPs. These findings provide a principled method for monitoring individual neurons without long-term recording of action potentials. PMID:25394574

  5. Binding-activated localization microscopy of DNA structures.

    PubMed

    Schoen, Ingmar; Ries, Jonas; Klotzsch, Enrico; Ewers, Helge; Vogel, Viola

    2011-09-14

    Many nucleic acid stains show a strong fluorescence enhancement upon binding to double-stranded DNA. Here we exploit this property to perform superresolution microscopy based on the localization of individual binding events. The dynamic labeling scheme and the optimization of fluorophore brightness yielded a resolution of ∼14 nm (fwhm) and a spatial sampling of 1/nm. We illustrate our approach with two different DNA-binding dyes and apply it to visualize the organization of the bacterial chromosome in fixed Escherichia coli cells. In general, the principle of binding-activated localization microscopy (BALM) can be extended to other dyes and targets such as protein structures. PMID:21838238

  6. Connecting local active forces to macroscopic stress in elastic media.

    PubMed

    Ronceray, Pierre; Lenz, Martin

    2015-02-28

    In contrast with ordinary materials, living matter drives its own motion by generating active, out-of-equilibrium internal stresses. These stresses typically originate from localized active elements embedded in an elastic medium, such as molecular motors inside the cell or contractile cells in a tissue. While many large-scale phenomenological theories of such active media have been developed, a systematic understanding of the emergence of stress from the local force-generating elements is lacking. In this paper, we present a rigorous theoretical framework to study this relationship. We show that the medium's macroscopic active stress tensor is equal to the active elements' force dipole tensor per unit volume in both continuum and discrete linear homogeneous media of arbitrary geometries. This relationship is conserved on average in the presence of disorder, but can be violated in nonlinear elastic media. Such effects can lead to either a reinforcement or an attenuation of the active stresses, giving us a glimpse of the ways in which nature might harness microscopic forces to create active materials. PMID:25594831

  7. Sensors at Centrosomes Reveal Determinants of Local Separase Activity

    PubMed Central

    Agircan, Fikret Gurkan; Schiebel, Elmar

    2014-01-01

    Separase is best known for its function in sister chromatid separation at the metaphase-anaphase transition. It also has a role in centriole disengagement in late mitosis/G1. To gain insight into the activity of separase at centrosomes, we developed two separase activity sensors: mCherry-Scc1(142-467)-ΔNLS-eGFP-PACT and mCherry-kendrin(2059-2398)-eGFP-PACT. Both localize to the centrosomes and enabled us to monitor local separase activity at the centrosome in real time. Both centrosomal sensors were cleaved by separase before anaphase onset, earlier than the corresponding H2B-mCherry-Scc1(142-467)-eGFP sensor at chromosomes. This indicates that substrate cleavage by separase is not synchronous in the cells. Depletion of the proteins astrin or Aki1, which have been described as inhibitors of centrosomal separase, did not led to a significant activation of separase at centrosomes, emphasizing the importance of direct separase activity measurements at the centrosomes. Inhibition of polo-like kinase Plk1, on the other hand, decreased the separase activity towards the Scc1 but not the kendrin reporter. Together these findings indicate that Plk1 regulates separase activity at the level of substrate affinity at centrosomes and may explain in part the role of Plk1 in centriole disengagement. PMID:25299182

  8. Effect of ferroelastic twin walls on local polarization switching: Phase-field modeling

    NASA Astrophysics Data System (ADS)

    Choudhury, S.; Zhang, J. X.; Li, Y. L.; Chen, L. Q.; Jia, Q. X.; Kalinin, S. V.

    2008-10-01

    Local polarization switching in epitaxial ferroelectric thin films in the presence of ferroelastic domain walls was studied using phase-field approach. The nucleation bias profile across a twin wall was analyzed, and the localization of preferential nucleation sites was established. This analysis was further extended to a realistic domain structure with multiple twin boundaries. It was observed that the local nucleation voltage required for a 180° domain switching is closely related to the number of such local defects.

  9. Effect of ferroelastic twin walls on local polarizations switching - phase field modeling

    SciTech Connect

    Jia, Quanzi; Choudhury, S; Zhang, J X; Li, Y L; Chen, Q; Kalinin, S V

    2008-01-01

    Local polarization switching in epitaxial ferroelectric thin films in the presence of ferroelastic domain walls was studied using phase-field approach. The nucleation bias profile across a twin wall was analyzed, and the localization of preferential nucleation sites was established. This analysis was further extended to a realistic domain structure with multiple twin boundaries. It was observed that the local nucleation voltage required for a 180{sup o} domain switching is closely related to the number of such local defects.

  10. Local Earth's gravity field in view of fractal dimension

    NASA Astrophysics Data System (ADS)

    Mészárosová, Katarína; Minarechová, Zuzana; Janák, Juraj

    2013-04-01

    The poster presents the relative roughness of chosen characteristics of the Earth's gravity field in several small regions in area of Slovakia (e.g. free-air anomaly, Bouguer anomaly, gravity disturbance...) using the values of fractal dimension. In this approach, a three dimensional box counting method and the Hurst analysis method are applied to estimate the values of fractal dimensions. Then the computed fractal dimension values are used to compare all 3D models of all chosen characteristics.

  11. Reinforcement active learning in the vibrissae system: optimal object localization.

    PubMed

    Gordon, Goren; Dorfman, Nimrod; Ahissar, Ehud

    2013-01-01

    Rats move their whiskers to acquire information about their environment. It has been observed that they palpate novel objects and objects they are required to localize in space. We analyze whisker-based object localization using two complementary paradigms, namely, active learning and intrinsic-reward reinforcement learning. Active learning algorithms select the next training samples according to the hypothesized solution in order to better discriminate between correct and incorrect labels. Intrinsic-reward reinforcement learning uses prediction errors as the reward to an actor-critic design, such that behavior converges to the one that optimizes the learning process. We show that in the context of object localization, the two paradigms result in palpation whisking as their respective optimal solution. These results suggest that rats may employ principles of active learning and/or intrinsic reward in tactile exploration and can guide future research to seek the underlying neuronal mechanisms that implement them. Furthermore, these paradigms are easily transferable to biomimetic whisker-based artificial sensors and can improve the active exploration of their environment. PMID:22789551

  12. An active UHF RFID localization system for fawn saving

    NASA Astrophysics Data System (ADS)

    Eberhardt, M.; Lehner, M.; Ascher, A.; Allwang, M.; Biebl, E. M.

    2015-11-01

    We present a localization concept for active UHF RFID transponders which enables mowing machine drivers to detect and localize marked fawns. The whole system design and experimental results with transponders located near the ground in random orientations in a meadow area are shown. The communication flow between reader and transponders is realized as a dynamic master-slave concept. Multiple marked fawns will be localized by processing detected transponders sequentially. With an eight-channel-receiver with integrated calibration method one can estimate the direction-of-arrival by measuring the phases of the transponder signals up to a range of 50 m in all directions. For further troubleshooting array manifolds have been measured. An additional hand-held receiver with a two-channel receiver allows a guided approaching search without endangering the fawn by the mowing machine.

  13. On the Energy Shift between Near-Field and Far-Field Peak Intensities in Localized Plasmon Systems

    SciTech Connect

    Zuloaga, Jorge; Nordlander, Peter

    2011-03-09

    The localized plasmons of metallic nanoparticles and nanostructures are known to display an interesting and apparently universal phenomenon: upon optical excitation, the maximum near-field enhancements occur at lower energies than the maximum of the corresponding far-field spectrum. Here we present an explanation for this behavior, showing that it results directly from the physics of a driven and damped harmonic oscillator. We show that the magnitude of the shift between the near- and far-field peak intensities depends directly on the total damping of the system, whether it is intrinsic damping within the metal of the nanoparticle or radiative damping of the localized plasmon.

  14. Switching local magnetization by electric-field-induced domain wall motion

    NASA Astrophysics Data System (ADS)

    Kakizakai, Haruka; Ando, Fuyuki; Koyama, Tomohiro; Yamada, Kihiro; Kawaguchi, Masashi; Kim, Sanghoon; Kim, Kab-Jin; Moriyama, Takahiro; Chiba, Daichi; Ono, Teruo

    2016-06-01

    Electric field effect on magnetism is an appealing technique for manipulating magnetization at a low energy cost. Here, we show that the local magnetization of an ultrathin Co film can be switched by simply applying a gate electric field without the assistance of any external magnetic field or current flow. The local magnetization switching is explained by nucleation and annihilation of magnetic domains through domain wall motion induced by the electric field. Our results lead to external-field-free and ultralow-energy spintronic applications.

  15. Insights into lateral marsh retreat mechanism through localized field measurements

    NASA Astrophysics Data System (ADS)

    Bendoni, M.; Mel, R.; Solari, L.; Lanzoni, S.; Francalanci, S.; Oumeraci, H.

    2016-02-01

    Deterioration of salt marshes may be due to several factors related to increased anthropic pressure, sea level rise, and erosive processes. While salt marshes can reach equilibrium in the vertical direction, adapting to sea level rise, they are inherently unstable in the horizontal direction. Marsh boundaries are characterized by scarps with bare sediment below the vegetated surface layer that can be easily removed by wave-induced erosion. In this work, we explore the different mechanisms involved in the erosion of marsh borders through the interpretation of field data. The analysis is based on a systematic field monitoring of a salt marsh in the Venice Lagoon subject to lateral erosion. Measurements included horizontal retreat of the scarp at various locations and wave height in front of the marsh during three storm surges. Continuous erosion and mass failures alternated during the observed period, leading to an average retreat up to 80 cm/yr. The data, collected roughly every month for 1.5 year, indicate that the linear relation that links the observed erosion rate to the impinging wave power exhibits a larger slope than that already estimated in literature on the basis of long-term surveys. Moreover, an increase in the gradient of erodibility is detected along the marsh scarp, due to the combined action of soil strengthening by vegetation on the marsh surface and the impact of wave breaking at the bank toe, which promote cantilever failures and increase the lateral erosion rate.

  16. Local implementation of cancer control activities in rural Appalachia, 2006.

    PubMed

    Behringer, Bruce; Mabe, Karen Harrell; Dorgan, Kelly A; Hutson, Sadie P

    2009-01-01

    Underserved communities with high cancer rates often are not involved in implementing state cancer control activities locally. An East Tennessee State University research team formed 2 Appalachian Community Cancer Research Review Work Groups, 1 in northeast Tennessee and 1 in southwest Virginia. During 4 sessions, the research team presented regional cancer data to the work groups. Work group participants explored research from a lay perspective and identified possible reasons for cancer disparities in central Appalachia. The fifth session was a community dissemination activity in which work group participants engaged in cancer education and action by presenting the research to their local communities in unique ways. During a sixth session, both work groups discussed these interventions and further attempted to answer the question, "What makes the experience of cancer unique in Appalachia?" This article describes the key steps of this community-based participatory research process. PMID:19080040

  17. Particle displacements in the elastic deformation of amorphous materials: Local fluctuations vs. non-affine field

    NASA Astrophysics Data System (ADS)

    Goldenberg, C.; Tanguy, A.; Barrat, J.-L.

    2007-10-01

    We study the local disorder in the deformation of amorphous materials by decomposing the particle displacements into a continuous, inhomogeneous field and the corresponding fluctuations. We compare these fields to the commonly used non-affine displacements in an elastically deformed 2D Lennard-Jones glass. Unlike the non-affine field, the fluctuations are very localized, and exhibit a much smaller (and system size independent) correlation length, on the order of a particle diameter, supporting the applicability of the notion of local "defects" to such materials. We propose a scalar "noise" field to characterize the fluctuations, as an additional field for extended continuum models, e.g., to describe the localized irreversible events observed during plastic deformation.

  18. Drug Trafficking Organizations and Local Economic Activity in Mexico

    PubMed Central

    González, Felipe

    2015-01-01

    Little is known about the relationship between illegal firms and local economic activity. In this paper I study changes in satellite night lights across Mexican municipalities after the arrival of large drug trafficking organizations in the period 2000–2010. After accounting for state trends and differences in political regimes, results indicate no significant change in night lights after the arrival of these illegal firms. Estimated coefficients are precise, robust, and similar across different drug trafficking organizations. PMID:26348041

  19. Drug Trafficking Organizations and Local Economic Activity in Mexico.

    PubMed

    González, Felipe

    2015-01-01

    Little is known about the relationship between illegal firms and local economic activity. In this paper I study changes in satellite night lights across Mexican municipalities after the arrival of large drug trafficking organizations in the period 2000-2010. After accounting for state trends and differences in political regimes, results indicate no significant change in night lights after the arrival of these illegal firms. Estimated coefficients are precise, robust, and similar across different drug trafficking organizations. PMID:26348041

  20. Two-dimensional atom localization in a four-level tripod system in laser fields

    SciTech Connect

    Ivanov, Vladimir; Rozhdestvensky, Yuri

    2010-03-15

    We propose a scheme for two-dimensional (2D) atom localization in a four-level tripod system under an influence of two orthogonal standing-wave fields. Position information of the atom is retained in the atomic internal states by an additional probe field either of a standing or of a running wave. It is shown that the localization factors depend crucially on the atom-field coupling that results in such spatial structures of populations as spikes, craters, and waves. We demonstrate a high-precision localization due to measurement of population in the upper state or in any ground state.

  1. Direct subwavelength imaging and control of near-field localization in individual silver nanocubes

    SciTech Connect

    Mårsell, Erik; Svärd, Robin; Miranda, Miguel; Guo, Chen; Harth, Anne; Lorek, Eleonora; Mauritsson, Johan; Arnold, Cord L.; L'Huillier, Anne; Mikkelsen, Anders; Losquin, Arthur; Xu, Hongxing

    2015-11-16

    We demonstrate the control of near-field localization within individual silver nanocubes through photoemission electron microscopy combined with broadband, few-cycle laser pulses. We find that the near-field is concentrated at the corners of the cubes, and that it can be efficiently localized to different individual corners depending on the polarization of the incoming light. The experimental results are confirmed by finite-difference time-domain simulations, which also provide an intuitive picture of polarization dependent near-field localization in nanocubes.

  2. Model of low-pass filtering of local field potentials in brain tissue

    NASA Astrophysics Data System (ADS)

    Bédard, C.; Kröger, H.; Destexhe, A.

    2006-05-01

    Local field potentials (LFPs) are routinely measured experimentally in brain tissue, and exhibit strong low-pass frequency filtering properties, with high frequencies (such as action potentials) being visible only at very short distances (≈10μm) from the recording electrode. Understanding this filtering is crucial to relate LFP signals with neuronal activity, but not much is known about the exact mechanisms underlying this low-pass filtering. In this paper, we investigate a possible biophysical mechanism for the low-pass filtering properties of LFPs. We investigate the propagation of electric fields and its frequency dependence close to the current source, i.e., at length scales in the order of average interneuronal distances. We take into account the presence of a high density of cellular membranes around current sources, such as glial cells. By considering them as passive cells, we show that under the influence of the electric source field, they respond by polarization. Because of the finite velocity of ionic charge movements, this polarization will not be instantaneous. Consequently, the induced electric field will be frequency-dependent, and much reduced for high frequencies. Our model establishes that this situation is analogous to an equivalent RC circuit, or better yet a system of coupled RC circuits. We present a number of numerical simulations of an induced electric field for biologically realistic values of parameters, and show the frequency filtering effect as well as the attenuation of extracellular potentials with distance. We suggest that induced electric fields in passive cells surrounding neurons are the physical origin of frequency filtering properties of LFPs. Experimentally testable predictions are provided allowing us to verify the validity of this model.

  3. An active antenna for ELF magnetic fields

    NASA Technical Reports Server (NTRS)

    Sutton, John F.; Spaniol, Craig

    1994-01-01

    The work of Nikola Tesla, especially that directed toward world-wide electrical energy distribution via excitation of the earth-ionosphere cavity resonances, has stimulated interest in the study of these resonances. Not only are they important for their potential use in the transmission of intelligence and electrical power, they are important because they are an integral part of our natural environment. This paper describes the design of a sensitive, untuned, low noise active antenna which is uniquely suited to modern earth-ionosphere cavity resonance measurements employing fast-Fourier transform techniques for near-real-time data analysis. It capitalizes on a little known field-antenna interaction mechanism. Recently, the authors made preliminary measurements of the magnetic fields in the earth-ionosphere cavity. During the course of this study, the problem of designing an optimized ELF magnetic field sensor presented itself. The sensor would have to be small, light weight (for portable use), and capable of detecting the 5-50 Hz picoTesla-level signals generated by the natural excitations of the earth-ionosphere cavity resonances. A review of the literature revealed that past researchers had employed very large search coils, both tuned and untuned. Hill and Bostick, for example, used coils of 30,000 turns wound on high permeability cores of 1.83 m length, weighing 40 kg. Tuned coils are unsuitable for modern fast-Fourier transform data analysis techniques which require a broad spectrum input. 'Untuned' coils connected to high input impedance voltage amplifiers exhibit resonant responses at the resonant frequency determined by the coil inductance and the coil distributed winding capacitance. Also, considered as antennas, they have effective areas equal only to their geometrical areas.

  4. Field Operations Program Activities Status Report

    SciTech Connect

    J. E. Francfort; D. V. O'Hara; L. A. Slezak

    1999-05-01

    The Field Operations Program is an electric vehicle testing and evaluation program sponsored by US Department of Energy and managed by the Idaho National Engineering and Environmental Laboratory. The Program's goals are to evaluate electric vehicles in real-world applications and environments, support electric vehicle technology advancement, develop infrastructure elements necessary to support significant electric vehicle use, support increased use of electric vehicles in federal fleets, and increase overall awareness and acceptance of electric vehicles. This report covers Program activities from fiscal year 1997 through mid-fiscal year 1999. The Field Operations Program succeeded the Site Operator Program, which ended in September 1996. Electric vehicle testing conducted by the Program includes baseline performance testing (EV America testing), accelerated reliability (life-cycle) testing, and fleet testing. The baseline performance parameters include accelerations, braking, range, energy efficiency, and charging time. The Program collects accelerated reliability and fleet operations data on electric vehicles operated by the Program's Qualified Vehicle Testing (QVT) partners. The Program's QVT partners have over 3 million miles of electric vehicle operating experience.

  5. Antifungal activity of local anesthetics against Candida species.

    PubMed Central

    Pina-Vaz, C; Rodrigues, A G; Sansonetty, F; Martinez-De-Oliveira, J; Fonseca, A F; Mårdh, P A

    2000-01-01

    OBJECTIVE: To evaluate the activity of benzydamine, lidocaine, and bupivacaine, three drugs with local anesthetic activity, against Candida albicans and non-albicans strains and to clarify their mechanism of activity. METHODS: The minimal inhibitory concentration (MIC) was determined for 20 Candida strains (18 clinical isolates and two American Type Culture Collection strains). The fungistatic activity was studied with the fluorescent probe FUN-1 and observation under epifluorescence microscopy and flow cytometry. The fungicidal activity of the three drugs was assayed by viability counts. Membrane alterations induced in the yeast cells were evaluated by staining with propidium iodide, by quantitation of intracellular K+ leakage and by transmission electron microscopy of intact yeast cells and prepared spheroplasts. RESULTS: The MIC ranged from 12.5-50.0 microg/mL, 5.0-40.0 mg/mL, and 2.5-10.0 mg/mL for benzydamine, lidocaine, and bupivacaine, respectively. The inhibitory activity of these concentrations could be detected with the fluorescent probe FUN-1 after incubation for 60 minutes. A very fast fungicidal activity was shown by 0.2, 50, and 30 mg/mL of benzydamine, lidocaine, and bupivacaine, respectively. CONCLUSIONS: At lower concentrations, the tested drugs have a fungistatic activity, due to yeast metabolic impairment, while at higher concentrations they are fungicidal, due to direct damage to the cytoplasmic membrane. PMID:10968594

  6. Subthalamic and Cortical Local Field Potentials Associated with Pilocarpine-Induced Oral Tremor in the Rat

    PubMed Central

    Long, Lauren L.; Podurgiel, Samantha J.; Haque, Aileen F.; Errante, Emily L.; Chrobak, James J.; Salamone, John D.

    2016-01-01

    Tremulous jaw movements (TJMs) are rapid vertical deflections of the lower jaw that resemble chewing but are not directed at any particular stimulus. In rodents, TJMs are induced by neurochemical conditions that parallel those seen in human Parkinsonism, including neurotoxic or pharmacological depletion of striatal dopamine (DA), DA antagonism, and cholinomimetic administration. Moreover, TJMs in rodents can be attenuated by antiparkinsonian agents, including levodopa (L-DOPA), DA agonists, muscarinic antagonists, and adenosine A2A antagonists. In human Parkinsonian patients, exaggerated physiological synchrony is seen in the beta frequency band in various parts of the cortical/basal ganglia/thalamic circuitry, and activity in the tremor frequency range (3–7 Hz) also has been recorded. The present studies were undertaken to determine if tremor-related local field potential (LFP) activity could be recorded from motor cortex (M1) or subthalamic nucleus (STN) during the TJMs induced by the muscarinic agonist pilocarpine, which is a well-known tremorogenic agent. Pilocarpine induced a robust TJM response that was marked by rhythmic electromyographic (EMG) activity in the temporalis muscle. Compared to periods with no tremor activity, TJM epochs were characterized by increased LFP activity in the tremor frequency range in both neocortex and STN. Tremor activity was not associated with increased synchrony in the beta frequency band. These studies identified tremor-related LFP activity in parts of the cortical/basal ganglia circuitry that are involved in the pathophysiology of Parkinsonism. This research may ultimately lead to identification of the oscillatory neural mechanisms involved in the generation of tremulous activity, and promote development of novel treatments for tremor disorders. PMID:27378874

  7. Fine structure of the magnetic field in active regions

    NASA Astrophysics Data System (ADS)

    Pustilnik, Lev; Beskrovnaya, Nina; Ikhsanov, Nazar

    High-resolution observations with SOHO, SDO, TRACE, HINODE suggest that the solar magnetic field in active regions has a complicated fine structure. There is a large number of thin magnetic arcs extended from the photosphere to corona with almost constant cross-section. We explore a possibility to model the complex of interacting arcs in terms of a dynamical percolating network. A transition of the system into flaring can be triggered by the flute instability of prominences and/or coronal condensations. We speculate around an assumption that the energy release in active regions is governed by the same scenario as dynamical current percolation through a random resistors network in which the saltatory conduction is controlled by a local current level.

  8. Ultrafast active control of localized surface plasmon resonances in silicon bowtie antennas.

    PubMed

    Berrier, Audrey; Ulbricht, Ronald; Bonn, Mischa; Rivas, Jaime Gómez

    2010-10-25

    Localized surface plasmon polaritons (LSPPs) provide an efficient means of achieving extreme light concentration. In recent years, their active control has become a major aspiration of plasmonic research. Here, we demonstrate direct control of semiconductor bowtie antennas, enabling active excitation of LSPPs, at terahertz (THz) frequencies. We modify the LSPPs by ultrafast optical modulation of the free carrier density in the plasmonic structure itself, allowing for active control of the semiconductor antennas on picosecond timescales. Moreover, this control enables the manipulation of the field intensity enhancements in ranges of four orders of magnitude. PMID:21164664

  9. Local anaesthetic activity of the essential oil of Lavandula angustifolia.

    PubMed

    Ghelardini, C; Galeotti, N; Salvatore, G; Mazzanti, G

    1999-12-01

    In this work we studied the local anaesthetic activity of the essential oil obtained from Lavandula angustifolia Mill., a medicinal plant traditionally used as an antispasmodic. We compared its activity to the essential oils obtained from two citrus fruits, Citrus reticulata Blanco and Citrus limon (L.) Burm. f., which have no medical uses. Biological tests were also performed on the major pure components of L. angustifolia Mill. essential oil: linalol and linalyl acetate as determined by GC and confirmed by GC-MS. Anaesthetic activity was evaluated in vivo in the rabbit conjunctival reflex test, and in vitro in a rat phrenic nerve-hemidiaphragm preparation. The essential oil of L. angustifolia, linalyl acetate and linanol (0.01-10 micrograms/ml) but not the oils of Citrus reticulata and Citrus limon were able to drastically reduce, in a dose-dependent manner, the electrically evoked contractions of rat phrenic-hemidiaphragm. In the rabbit conjunctival reflex test treatment with a solution of essential oil of L. angustifolia, as well as linalyl acetate and linalol (30-2500 micrograms/ml administered in the conjunctival sac) allow a dose-dependent increase in the number of stimuli necessary to provoke the reflex, thus confirming in vivo the local anaesthetic activity observed in vitro. PMID:10630108

  10. Active contours for localizing polyps in colonoscopic NBI image data

    NASA Astrophysics Data System (ADS)

    Breier, Matthias; Gross, Sebastian; Behrens, Alexander; Stehle, Thomas; Aach, Til

    2011-03-01

    Colon cancer is the third most common type of cancer in the United States of America. Every year about 140,000 people are newly diagnosed with colon cancer. Early detection is crucial for a successful therapy. The standard screening procedure is called colonoscopy. Using this endoscopic examination physicians can find colon polyps and remove them if necessary. Adenomatous colon polyps are deemed a preliminary stage of colon cancer. The removal of a polyp, though, can lead to complications like severe bleedings or colon perforation. Thus, only polyps diagnosed as adenomatous should be removed. To decide whether a polyp is adenomatous the polyp's surface structure including vascular patterns has to be inspected. Narrow-Band imaging (NBI) is a new tool to improve visibility of vascular patterns of the polyps. The first step for an automatic polyp classification system is the localization of the polyp. We investigate active contours for the localization of colon polyps in NBI image data. The shape of polyps, though roughly approximated by an elliptic form, is highly variable. Active contours offer the flexibility to adapt to polyp variation well. To avoid clustering of contour polygon points we propose the application of active rays. The quality of the results was evaluated based on manually segmented polyps as ground truth data. The results were compared to a template matching approach and to the Generalized Hough Transform. Active contours are superior to the Hough transform and perform equally well as the template matching approach.

  11. Histochemical localization of palmitoyl protein thioesterase-1 activity.

    PubMed

    Dearborn, Joshua T; Ramachandran, Subramania; Shyng, Charles; Lu, Jui-Yun; Thornton, Jonah; Hofmann, Sandra L; Sands, Mark S

    2016-02-01

    Infantile neuronal ceroid lipofuscinosis (INCL, Infantile Batten disease) is an invariably fatal neurodegenerative pediatric disorder caused by an inherited mutation in the PPT1 gene. Patients with INCL lack the lysosomal enzyme palmitoyl protein thioesterase-1 (PPT1, EC 3.1.2.22), resulting in intracellular accumulation of autofluorescent storage material and subsequent neuropathology. The Ppt1(-/-) mouse is deficient in PPT1 activity and represents a useful animal model of INCL that recapitulates most of the clinical and pathological aspects of the disease. Preclinical therapeutic experiments performed in the INCL mouse include CNS-directed gene therapy and recombinant enzyme replacement therapy; both seek to re-establish therapeutic levels of the deficient enzyme. We present a novel method for the histochemical localization of PPT1 activity in the Ppt1(-/-) mouse. By utilizing the substrate CUS-9235, tissues known to be positive for PPT1 activity turn varying intensities of blue. Presented here are histochemistry data showing the staining pattern in Ppt1(-/-), wild type, and Ppt1(-/-) mice treated with enzyme replacement therapy or AAV2/9-PPT1-mediated gene therapy. Results are paired with quantitative biochemistry data that confirm the ability of CUS-9235 to detect and localize PPT1 activity. This new method complements the current tools for the study of INCL and evaluation of effective therapies. PMID:26597320

  12. Local Health Department Activities to Ensure Access to Care

    PubMed Central

    Luo, Huabin; Sotnikov, Sergey; Shah, Gulzar

    2016-01-01

    Background Local health departments (LHDs) can play an important role in linking people to personal health services and ensuring the provision of health care when it is otherwise unavailable. However, the extent to which LHDs are involved in ensuring access to health care in its jurisdictions is not well known. Purpose To provide nationally representative estimates of LHD involvement in specific activities to ensure access to healthcare services and to assess their association with macro-environment/community and LHD capacity and process characteristics. Methods Data used were from the 2010 National Profile of Local Health Departments Study, Area Resource Files, and the Association of State and Territorial Health Officials’ 2010 Profile of State Public Health Agencies Survey. Data were analyzed in 2012. Results Approximately 66.0% of LHDs conducted activities to ensure access to medical care, 45.9% to dental care, and 32.0% to behavioral health care. About 28% of LHDs had not conducted activities to ensure access to health care in their jurisdictions in 2010. LHDs with higher per capita expenditures and larger jurisdiction population sizes were more likely to provide access to care services (p <0.05). Conclusions There is substantial variation in LHD engagement in activities to ensure access to care. Differences in LHD capacity and the needs of the communities in which they are located may account for this variation. Further research is needed to determine whether this variation is associated with adverse population health outcomes. PMID:24237913

  13. Estimated number of field stars toward Galactic globular clusters and Local Group Galaxies

    NASA Technical Reports Server (NTRS)

    Ratnatunga, K. U.; Bahcall, J. N.

    1985-01-01

    Field star densities are estimated for 89 fields with /b/ greater than 10 degrees based on the Galaxy model of Bahcall and Soneira (1980, 1984; Bahcall et al. 1985). Calculated tables are presented for 76 of the fields toward Galactic globular clusters, and 16 Local Group Galaxies in 13 fields. The estimates can be used as an initial guide for planning both ground-based and Space Telescope observations of globular clusters at intermediate-to-high Galactic latitudes.

  14. Localization of incipient tip vortex cavitation using ray based matched field inversion method

    NASA Astrophysics Data System (ADS)

    Kim, Dongho; Seong, Woojae; Choo, Youngmin; Lee, Jeunghoon

    2015-10-01

    Cavitation of marine propeller is one of the main contributing factors of broadband radiated ship noise. In this research, an algorithm for the source localization of incipient vortex cavitation is suggested. Incipient cavitation is modeled as monopole type source and matched-field inversion method is applied to find the source position by comparing the spatial correlation between measured and replicated pressure fields at the receiver array. The accuracy of source localization is improved by broadband matched-field inversion technique that enhances correlation by incoherently averaging correlations of individual frequencies. Suggested localization algorithm is verified through known virtual source and model test conducted in Samsung ship model basin cavitation tunnel. It is found that suggested localization algorithm enables efficient localization of incipient tip vortex cavitation using a few pressure data measured on the outer hull above the propeller and practically applicable to the typically performed model scale experiment in a cavitation tunnel at the early design stage.

  15. Geodesic active fields--a geometric framework for image registration.

    PubMed

    Zosso, Dominique; Bresson, Xavier; Thiran, Jean-Philippe

    2011-05-01

    In this paper we present a novel geometric framework called geodesic active fields for general image registration. In image registration, one looks for the underlying deformation field that best maps one image onto another. This is a classic ill-posed inverse problem, which is usually solved by adding a regularization term. Here, we propose a multiplicative coupling between the registration term and the regularization term, which turns out to be equivalent to embed the deformation field in a weighted minimal surface problem. Then, the deformation field is driven by a minimization flow toward a harmonic map corresponding to the solution of the registration problem. This proposed approach for registration shares close similarities with the well-known geodesic active contours model in image segmentation, where the segmentation term (the edge detector function) is coupled with the regularization term (the length functional) via multiplication as well. As a matter of fact, our proposed geometric model is actually the exact mathematical generalization to vector fields of the weighted length problem for curves and surfaces introduced by Caselles-Kimmel-Sapiro. The energy of the deformation field is measured with the Polyakov energy weighted by a suitable image distance, borrowed from standard registration models. We investigate three different weighting functions, the squared error and the approximated absolute error for monomodal images, and the local joint entropy for multimodal images. As compared to specialized state-of-the-art methods tailored for specific applications, our geometric framework involves important contributions. Firstly, our general formulation for registration works on any parametrizable, smooth and differentiable surface, including nonflat and multiscale images. In the latter case, multiscale images are registered at all scales simultaneously, and the relations between space and scale are intrinsically being accounted for. Second, this method is, to

  16. Classical field theories from Hamiltonian constraint: Canonical equations of motion and local Hamilton-Jacobi theory

    NASA Astrophysics Data System (ADS)

    Zatloukal, Václav

    2016-04-01

    Classical field theory is considered as a theory of unparametrized surfaces embedded in a configuration space, which accommodates, in a symmetric way, spacetime positions and field values. Dynamics is defined by a (Hamiltonian) constraint between multivector-valued generalized momenta, and points in the configuration space. Starting from a variational principle, we derive local equations of motion, that is, differential equations that determine classical surfaces and momenta. A local Hamilton-Jacobi equation applicable in the field theory then follows readily. The general method is illustrated with three examples: non-relativistic Hamiltonian mechanics, De Donder-Weyl scalar field theory, and string theory.

  17. Endoplasmic reticulum localization and activity of maize auxin biosynthetic enzymes.

    PubMed

    Kriechbaumer, Verena; Seo, Hyesu; Park, Woong June; Hawes, Chris

    2015-09-01

    Auxin is a major growth hormone in plants and the first plant hormone to be discovered and studied. Active research over >60 years has shed light on many of the molecular mechanisms of its action including transport, perception, signal transduction, and a variety of biosynthetic pathways in various species, tissues, and developmental stages. The complexity and redundancy of the auxin biosynthetic network and enzymes involved raises the question of how such a system, producing such a potent agent as auxin, can be appropriately controlled at all. Here it is shown that maize auxin biosynthesis takes place in microsomal as well as cytosolic cellular fractions from maize seedlings. Most interestingly, a set of enzymes shown to be involved in auxin biosynthesis via their activity and/or mutant phenotypes and catalysing adjacent steps in YUCCA-dependent biosynthesis are localized to the endoplasmic reticulum (ER). Positioning of auxin biosynthetic enzymes at the ER could be necessary to bring auxin biosynthesis in closer proximity to ER-localized factors for transport, conjugation, and signalling, and allow for an additional level of regulation by subcellular compartmentation of auxin action. Furthermore, it might provide a link to ethylene action and be a factor in hormonal cross-talk as all five ethylene receptors are ER localized. PMID:26139824

  18. Reconstructing Grasping Motions from High-Frequency Local Field Potentials in Primary Motor Cortex

    PubMed Central

    Zhuang, Jun; Truccolo, Wilson; Vargas-Irwin, Carlos; Donoghue, John P.

    2011-01-01

    Recent developments in neural interface systems hold the promise to restore movement in people with paralysis. In search of neural signals for control of neural interface systems (NISs), previous studies have investigated primarily single and multiunit activity, as well as low frequency local field potentials (LFPs). In this paper, we investigate the information content about grasping motion of a broad band high frequency LFP (200 Hz – 400 Hz) by classifying discrete grasp aperture states and decoding continuous aperture trajectories. LFPs were recorded via 96-microelectrode arrays in the primary motor cortex (M1) of two monkeys performing free 3-D reaching and grasping towards moving objects. Our results indicate that broad band high frequency LFPs could serve as useful signals in NISs that aim at restoring motor functions such as grasp control. PMID:21096002

  19. Computational Modeling of Single Neuron Extracellular Electric Potentials and Network Local Field Potentials using LFPsim.

    PubMed

    Parasuram, Harilal; Nair, Bipin; D'Angelo, Egidio; Hines, Michael; Naldi, Giovanni; Diwakar, Shyam

    2016-01-01

    Local Field Potentials (LFPs) are population signals generated by complex spatiotemporal interaction of current sources and dipoles. Mathematical computations of LFPs allow the study of circuit functions and dysfunctions via simulations. This paper introduces LFPsim, a NEURON-based tool for computing population LFP activity and single neuron extracellular potentials. LFPsim was developed to be used on existing cable compartmental neuron and network models. Point source, line source, and RC based filter approximations can be used to compute extracellular activity. As a demonstration of efficient implementation, we showcase LFPs from mathematical models of electrotonically compact cerebellum granule neurons and morphologically complex neurons of the neocortical column. LFPsim reproduced neocortical LFP at 8, 32, and 56 Hz via current injection, in vitro post-synaptic N2a, N2b waves and in vivo T-C waves in cerebellum granular layer. LFPsim also includes a simulation of multi-electrode array of LFPs in network populations to aid computational inference between biophysical activity in neural networks and corresponding multi-unit activity resulting in extracellular and evoked LFP signals. PMID:27445781

  20. Computational Modeling of Single Neuron Extracellular Electric Potentials and Network Local Field Potentials using LFPsim

    PubMed Central

    Parasuram, Harilal; Nair, Bipin; D'Angelo, Egidio; Hines, Michael; Naldi, Giovanni; Diwakar, Shyam

    2016-01-01

    Local Field Potentials (LFPs) are population signals generated by complex spatiotemporal interaction of current sources and dipoles. Mathematical computations of LFPs allow the study of circuit functions and dysfunctions via simulations. This paper introduces LFPsim, a NEURON-based tool for computing population LFP activity and single neuron extracellular potentials. LFPsim was developed to be used on existing cable compartmental neuron and network models. Point source, line source, and RC based filter approximations can be used to compute extracellular activity. As a demonstration of efficient implementation, we showcase LFPs from mathematical models of electrotonically compact cerebellum granule neurons and morphologically complex neurons of the neocortical column. LFPsim reproduced neocortical LFP at 8, 32, and 56 Hz via current injection, in vitro post-synaptic N2a, N2b waves and in vivo T-C waves in cerebellum granular layer. LFPsim also includes a simulation of multi-electrode array of LFPs in network populations to aid computational inference between biophysical activity in neural networks and corresponding multi-unit activity resulting in extracellular and evoked LFP signals. PMID:27445781

  1. SARM1 activation triggers axon degeneration locally via NAD+ destruction

    PubMed Central

    Gerdts, Josiah; Brace, E.J.; Sasaki, Yo; DiAntonio, Aaron

    2015-01-01

    Axon degeneration is an intrinsic self-destruction program that underlies axon loss during injury and disease. Sterile alpha and TIR motif containing 1 (SARM1) protein is an essential mediator of axon degeneration. We report that SARM1 initiates a local destruction program involving rapid breakdown of NAD+ after injury. We used an engineered protease-sensitized SARM1 to demonstrate that SARM1 activity is required after axon injury to induce axon degeneration. Dimerization of the Toll-Interleukin Receptor (TIR) domain of SARM1 alone was sufficient to induce locally-mediated axon degeneration. Formation of the SARM1 TIR dimer triggered rapid breakdown of NAD+, whereas SARM1-induced axon destruction could be counteracted by increased NAD+ synthesis. SARM1-induced depletion of NAD+ may explain the potent axon protection in Wallerian Degeneration slow (Wlds) mutant mice. PMID:25908823

  2. Role Of Conjugate and Local Terminators On the Electric Fields at Arecibo

    NASA Astrophysics Data System (ADS)

    Ganguly, S.; Brum, C. G. M.; Aponte, N.; Franco, E.; Gonzalez, S. A.

    2014-12-01

    Using some recent Plasma drift data at Arecibo, we present evidences of Electric Field (E) changes induced by sunrise and sunset transitions at both local and conjugate regions. Field perpendicular plasma drifts in the F region are used as unambiguous diagnostic of the Electric Field. The large time differences between the local ( 18.35 N, 66.75 W) and conjugate region (46.6 S, 64.7 W) sunrise and sunsets, particularly during the local winter at Arecibo, allow identification of local and conjugate effects on the E field. We present evidences of a downward velocity started around the conjugate sunrise and reaching minimum around the local sunrise, when it turns around and merges with normal daytime behavior, controlled by the dynamo region. During sunset, the upward drift increase at local sunset and shows a dip at the conjugate sunset, when it turns around. Afterwards, the F region is isolated and behaves in regular night time fashion. The entire behavior can be explained by coupled behavior of the E and F region, where the terminator line switches the coupling and affects charge separation at the boundaries. Similar investigations using the summer data have been performed and confirm the interpretation of coupled electric circuit including the local and conjugate regions and intervening ionosphere along the field lines.

  3. Externally controlled local magnetic field in a conducting mesoscopic ring coupled to a quantum wire

    SciTech Connect

    Maiti, Santanu K.

    2015-01-14

    In the present work, the possibility of regulating local magnetic field in a quantum ring is investigated theoretically. The ring is coupled to a quantum wire and subjected to an in-plane electric field. Under a finite bias voltage across the wire a net circulating current is established in the ring which produces a strong magnetic field at its centre. This magnetic field can be tuned externally in a wide range by regulating the in-plane electric field, and thus, our present system can be utilized to control magnetic field at a specific region. The feasibility of this quantum system in designing spin-based quantum devices is also analyzed.

  4. Anderson localization with second quantized fields in a coupled array of waveguides

    SciTech Connect

    Thompson, Clinton; Vemuri, Gautam; Agarwal, G. S.

    2010-11-15

    We report a theoretical study of Anderson localization of nonclassical light in an array of waveguides in which neighboring waveguides are evanescently coupled and in which the disorder can be added in a controlled manner. We use squeezed light at the input to investigate the effects of nonclassicality and compare the results with those obtained by using conventional classical fields, such as a coherent field and a Gaussian field. Our results show that there is an enhancement in fluctuations of localized light due to the medium's disorder. We find superbunching of the localized light, which may be useful for enhancing the interaction between radiation and matter. Another important consequence of sub-Poissonian statistics of the incoming light is to quench the total fluctuations at the output. Finally, we show that as a result of the multiplicative noise in the problem, the output field is far from Gaussian even if the input is a coherent field.

  5. Nano-fEM: Protein Localization Using Photo-activated Localization Microscopy and Electron Microscopy

    PubMed Central

    Watanabe, Shigeki; Richards, Jackson; Hollopeter, Gunther; Hobson, Robert J.; Davis, Wayne M.; Jorgensen, Erik M.

    2012-01-01

    Mapping the distribution of proteins is essential for understanding the function of proteins in a cell. Fluorescence microscopy is extensively used for protein localization, but subcellular context is often absent in fluorescence images. Immuno-electron microscopy, on the other hand, can localize proteins, but the technique is limited by a lack of compatible antibodies, poor preservation of morphology and because most antigens are not exposed to the specimen surface. Correlative approaches can acquire the fluorescence image from a whole cell first, either from immuno-fluorescence or genetically tagged proteins. The sample is then fixed and embedded for electron microscopy, and the images are correlated 1-3. However, the low-resolution fluorescence image and the lack of fiducial markers preclude the precise localization of proteins. Alternatively, fluorescence imaging can be done after preserving the specimen in plastic. In this approach, the block is sectioned, and fluorescence images and electron micrographs of the same section are correlated 4-7. However, the diffraction limit of light in the correlated image obscures the locations of individual molecules, and the fluorescence often extends beyond the boundary of the cell. Nano-resolution fluorescence electron microscopy (nano-fEM) is designed to localize proteins at nano-scale by imaging the same sections using photo-activated localization microscopy (PALM) and electron microscopy. PALM overcomes the diffraction limit by imaging individual fluorescent proteins and subsequently mapping the centroid of each fluorescent spot 8-10. We outline the nano-fEM technique in five steps. First, the sample is fixed and embedded using conditions that preserve the fluorescence of tagged proteins. Second, the resin blocks are sectioned into ultrathin segments (70-80 nm) that are mounted on a cover glass. Third, fluorescence is imaged in these sections using the Zeiss PALM microscope. Fourth, electron dense structures are imaged

  6. Non-locality in quantum field theory due to general relativity

    NASA Astrophysics Data System (ADS)

    Calmet, Xavier; Croon, Djuna; Fritz, Christopher

    2015-12-01

    We show that general relativity coupled to a quantum field theory generically leads to non-local effects in the matter sector. These non-local effects can be described by non-local higher dimensional operators which remarkably have an approximate shift symmetry. When applied to inflationary models, our results imply that small non-Gaussianities are a generic feature of models based on general relativity coupled to matter fields. However, these effects are too small to be observable in the cosmic microwave background.

  7. Stimulated Brillouin scattering in the field of a two-dimensionally localized pumping wave

    NASA Astrophysics Data System (ADS)

    Solikhov, D. K.; Dvinin, S. A.

    2016-06-01

    Stimulated Brillouin scattering of electromagnetic waves in the field of a two-dimensionally localized pump wave at arbitrary scattering angles in the regime of forward scattering is analyzed. Spatial variations in the amplitudes of interacting waves are studied for different values of the pump field and different dimensions of the pump wave localization region. The intensity of scattered radiation is determined as a function of the scattering angle and the dimensions of the pump wave localization region. It is shown that the intensity increases with increasing scattering angle.

  8. Near-field localization by two dimensional metallic nano-post arrays with ultrashort light pulses

    NASA Astrophysics Data System (ADS)

    Lee, Hongki; Kim, Chulhong; Kim, Donghyun

    2016-03-01

    Locally amplified near-fields can be induced with nanostructures within a sub-diffraction-limited volume, which is useful for biomedical imaging and sensing applications. Employment of field localization in the biomedical applications where the pulsed light is used necessitates the spatial and temporal characteristics of fields near nanostructures. We considered the gold nano-post arrays of three different shapes to localize the near-fields which are circular, rhombic, and triangular. They were modeled to be located on an ITO film and a quartz substrate with periods changing from 300 to 900 nm by 200 nm. Their size changes from 50 to 250 nm which corresponds to the radius for the case of circular nanoposts and the distance between the center and the vertices for equilateral rhombic and triangular nanoposts. Numerical calculation of near-fields at the top of nanoposts was performed with finite difference time domain method when the Gaussian pulses at center wavelengths of 532, 633, and 850 nm were normally incident. Near-fields localization occurred mainly at vertices of the nanoposts, which makes the triangular nanoposts of primary interest with an observation of the strongest field intensity within a diffraction limited field-of-view. The observed fields on the triangular vertices were enhanced by 7.85, 51.54, and 7268 when the center wavelengths were 532, 633, and 850 nm respectively. Their temporal peaks were delayed by 2.05, 4.03, and 14.49 fs, which indicates the correlation between field enhancement and time delay associated with electron damping process. It was shown that with rhombic and triangular nanoposts fields can be localized below 10 nm on vertices and their signal-to-noise ratio increased with a larger period.

  9. The continuum intensity as a function of magnetic field. II. Local magnetic flux and convective flows

    NASA Astrophysics Data System (ADS)

    Kobel, P.; Solanki, S. K.; Borrero, J. M.

    2012-06-01

    Context. To deepen our understanding of the role of small-scale magnetic fields in active regions (ARs) and in the quiet Sun (QS) on the solar irradiance, it is fundamental to investigate the physical processes underlying their continuum brightness. Previous results showed that magnetic elements in the QS reach larger continuum intensities than in ARs at disk center, but left this difference unexplained. Aims: We use Hinode/SP disk center data to study the influence of the local amount of magnetic flux on the vigour of the convective flows and the continuum intensity contrasts. Methods: The apparent (i.e. averaged over a pixel) longitudinal field strength and line-of-sight (LOS) plasma velocity were retrieved by means of Milne-Eddington inversions (VFISV code). We analyzed a series of boxes taken over AR plages and the QS, to determine how the continuum intensity contrast of magnetic elements, the amplitude of the vertical flows and the box-averaged contrast were affected by the mean longitudinal field strength in the box (which scales with the total unsigned flux in the box). Results: Both the continuum brightness of the magnetic elements and the dispersion of the LOS velocities anti-correlate with the mean longitudinal field strength. This can be attributed to the "magnetic patches" (here defined as areas where the longitudinal field strength is above 100 G) carrying most of the flux in the boxes. There the velocity amplitude and the spatial scale of convection are reduced. Due to this hampered convective transport, these patches appear darker than their surroundings. Consequently, the average brightness of a box decreases as the the patches occupy a larger fraction of it and the amount of embedded flux thereby increases. Conclusions: Our results suggest that as the magnetic flux increases locally (e.g. from weak network to strong plage), the heating of the magnetic elements is reduced by the intermediate of a more suppressed convective energy transport within

  10. Lower arm electromyography (EMG) activity detection using local binary patterns.

    PubMed

    McCool, Paul; Chatlani, Navin; Petropoulakis, Lykourgos; Soraghan, John J; Menon, Radhika; Lakany, Heba

    2014-09-01

    This paper presents a new electromyography activity detection technique in which 1-D local binary pattern histograms are used to distinguish between periods of activity and inactivity in myoelectric signals. The algorithm is tested on forearm surface myoelectric signals occurring due to hand gestures. The novel features of the presented method are that: 1) activity detection is performed across multiple channels using few parameters and without the need for majority vote mechanisms, 2) there are no per-channel thresholds to be tuned, which makes the process of activity detection easier and simpler to implement and less prone to errors, 3) it is not necessary to measure the properties of the signal during a quiescent period before using the algorithm. The algorithm is compared to other offline single- and double-threshold activity detection methods and, for the data sets tested, it is shown to have a better overall performance with greater tolerance to the noise in the real data set used. PMID:24802139

  11. Stabilization of the Vertical Mode in Tokamaks by Localized Nonaxisymmetric Fields

    SciTech Connect

    A. Reiman

    2007-10-02

    Vertical instability of a tokamak plasma can be controlled by nonaxisymmetric magnetic fields localized near the plasma edge at the bottom and top of the torus. The required magnetic fields can be produced by a relatively simple set of parallelogram-shaped coils.

  12. Local field enhancement on metallic periodic surface structures produced by femtosecond laser pulses

    SciTech Connect

    Ionin, Andrei A; Kudryashov, Sergei I; Ligachev, A E; Makarov, Sergei V; Mel'nik, N N; Rudenko, A A; Seleznev, L V; Sinitsyn, D V; Khmelnitskii, R A

    2013-04-30

    Periodic surface structures on aluminium are produced by femtosecond laser pulses for efficient excitation of surface electromagnetic waves using a strong objective (NA = 0.5). The local electromagnetic field enhancement on the structures is measured using the technique of surface-enhanced Raman scattering from pyridine molecules. (extreme light fields and their applications)

  13. Dynamical localization of Dirac particles in electromagnetic fields with dominating magnetic potentials

    NASA Astrophysics Data System (ADS)

    Barbaroux, Jean-Marie; Mehringer, Josef; Stockmeyer, Edgardo; Taarabt, Amal

    2016-04-01

    We consider two-dimensional massless Dirac operators in a radially symmetric electromagnetic field. In this case the fields may be described by one-dimensional electric and magnetic potentials V and A. We show dynamical localization in the regime when lim r → ∞ ⁡ | V | / | A | < 1, where dense point spectrum occurs.

  14. Using human extra-cortical local field potentials to control a switch

    NASA Astrophysics Data System (ADS)

    Kennedy, Philip; Andreasen, Dinal; Ehirim, Princewill; King, Brandon; Kirby, Todd; Mao, Hui; Moore, Melody

    2004-06-01

    Individuals with profound paralysis and mutism require a communication channel. Traditional assistive technology devices eventually fail, especially in the case of amyotrophic lateral sclerosis (ALS) subjects who gradually become totally locked-in. A direct brain-to-computer interface that provides switch functions can provide a direct communication channel to the external world. Electroencephalographic (EEG) signals recorded from scalp electrodes are significantly degraded due to skull and scalp attenuation and ambient noise. The present system using conductive skull screws allows more reliable access to cortical local field potentials (LFPs) without entering the brain itself. We describe an almost locked-in human subject with ALS who activated a switch using online time domain detection techniques. Frequency domain analysis of his LFP activity demonstrates this to be an alternative method of detecting switch activation intentions. With this brain communicator system it is reasonable to expect that locked-in, but cognitively intact, humans will always be able to communicate. Financial disclosure. Authors PK and DA may derive some financial gain from the sale of this device. A patent has been applied under US and international law: 10/675,703.

  15. Deformation-induced spatiotemporal fluctuation, evolution and localization of strain fields in a bulk metallic glass

    SciTech Connect

    Wu, Yuan; Bei, Hongbin; Wang, Yanli; Lu, Zhaoping; George, Easo P.; Gao, Yanfei

    2015-05-16

    Deformation behavior and local strain evolutions upon loading and unloading of a bulk metallic glass (BMG) were systematically investigated by in situ digital image correlation (DIC). Distinct fluctuations and irreversible local strains were observed before the onset of macroscopic yielding. Statistical analysis shows that these fluctuations might be related to intrinsic structural heterogeneities, and that the evolution history and characteristics of local strain fields play an important role in the subsequent initiation of shear bands. Effects of sample size, pre-strain, and loading conditions were systematically analyzed in terms of the probability distributions of the resulting local strain fields. It is found that a higher degree of local shear strain heterogeneity corresponds to a more ductile stressestrain curve. Implications of these findings are discussed for the design of new materials.

  16. Deformation-induced spatiotemporal fluctuation, evolution and localization of strain fields in a bulk metallic glass

    DOE PAGESBeta

    Wu, Yuan; Bei, Hongbin; Wang, Yanli; Lu, Zhaoping; George, Easo P.; Gao, Yanfei

    2015-05-16

    Deformation behavior and local strain evolutions upon loading and unloading of a bulk metallic glass (BMG) were systematically investigated by in situ digital image correlation (DIC). Distinct fluctuations and irreversible local strains were observed before the onset of macroscopic yielding. Statistical analysis shows that these fluctuations might be related to intrinsic structural heterogeneities, and that the evolution history and characteristics of local strain fields play an important role in the subsequent initiation of shear bands. Effects of sample size, pre-strain, and loading conditions were systematically analyzed in terms of the probability distributions of the resulting local strain fields. It ismore » found that a higher degree of local shear strain heterogeneity corresponds to a more ductile stressestrain curve. Implications of these findings are discussed for the design of new materials.« less

  17. Local conductance: A means to extract polarization and depolarizing fields near domain walls in ferroelectrics

    SciTech Connect

    Douglas, A. M.; Kumar, A.; Gregg, J. M.; Whatmore, R. W.

    2015-10-26

    Conducting atomic force microscopy images of bulk semiconducting BaTiO{sub 3} surfaces show clear stripe domain contrast. High local conductance correlates with strong out-of-plane polarization (mapped independently using piezoresponse force microscopy), and current-voltage characteristics are consistent with dipole-induced alterations in Schottky barriers at the metallic tip-ferroelectric interface. Indeed, analyzing current-voltage data in terms of established Schottky barrier models allows relative variations in the surface polarization, and hence the local domain structure, to be determined. Fitting also reveals the signature of surface-related depolarizing fields concentrated near domain walls. Domain information obtained from mapping local conductance appears to be more surface-sensitive than that from piezoresponse force microscopy. In the right materials systems, local current mapping could therefore represent a useful complementary technique for evaluating polarization and local electric fields with nanoscale resolution.

  18. Sensitivity to local dipole fields in the CRAZED experiment: An approach to bright spot MRI

    NASA Astrophysics Data System (ADS)

    Faber, Cornelius; Heil, Carolin; Zahneisen, Benjamin; Balla, David Z.; Bowtell, Richard

    2006-10-01

    Local dipole fields such as those created by small iron-oxide particles are used to produce regions of low intensity (dark contrast) in many molecular magnetic resonance imaging applications. We have investigated, with computer simulations and experiments at 17.6 T, how the COSY revamped with asymmetric z-gradient echo detection (CRAZED) experiment that selects intermolecular double-quantum coherences can also be used to visualize such local dipole fields. Application of the coherence-selection gradient pulses parallel to the main magnetic field produced similar, dark contrast as conventional gradient echo imaging. Application of the gradient along the magic angle leads to total loss of signal intensity in homogeneous samples. In the presence of local dipole fields, the contrast was inverted and bright signals from the dipoles were observed over a very low background. Both simulations and experiments showed that the signal strongly decreased when a phase-cycle suppressing single-quantum coherences was employed. Therefore, we conclude that most of the signal comes from directly refocused magnetization or intermolecular single-quantum coherences. Finally, we demonstrate that bright contrast from local dipole fields can also be obtained, when the pair of coherence-selection gradient pulses is deliberately mismatched. Both methods allowed visualization of local dipole fields in phantoms in experimental times of about 3 min.

  19. Passive versus active local microrheology in mammalian cells and amoebae

    NASA Astrophysics Data System (ADS)

    Riviere, C.; Gazeau, F.; Marion, S.; Bacri, J.-C.; Wilhelm, C.

    2004-12-01

    We compare in this paper the rotational magnetic microrheology detailed by Marion et al [18] and Wilhelm et al [19] to the passive tracking microrheology. The rotational microrheology has been designed to explore, using magnetic rotating probes, the local intracellular microenvironment of living cells in terms of viscoelasticity. Passive microrheology techniques is based on the analysis of spontaneous diffusive motions of Brownian probes. The dependence of mean square displacement (MSD) with the time then directly reflects the type of movement (sub-, hyper- or diffusive motions). Using the same intracellular probes, we performed two types of measurements (active and passive). Based on the fluctuation-dissipation theorem, one should obtain the same information from the both techniques in a thermally equilibrium system. Interestingly, our measurements differ, and the discordances directly inform on active biological processes, which add to thermally activated fluctuations in our out-of equilibrium systems. In both cell models used, mammalian Hela cells and amoebae Entamoeba Histolytica, a hyper-diffusive regime at a short time is observed, which highlights the presence of an active non-thermal driving force, acting on the probe. However, the nature of this active force in mammalian cells and amoebae is different, according to their different phenotypes. In mammalian cells active processes are governed by the transport, via molecular motors, on the microtubule network. In amoebae, which are highly motile cells free of microtubule network, the active processes are dominated by strong fluxes of cytoplasm driven by extension of pseudopodia, in random directions, leading to an amplitude of motion one order of magnitude higher than for mammalian cells. Figs 7, Refs 32.

  20. The impacts of local human activities on the Antarctic environment

    NASA Astrophysics Data System (ADS)

    Tin, T.; Fleming, Z. L.; Hughes, K. A.; Ainley, D. G.; Convey, P.; Moreno, C. A.; Pfeiffer, S.; Scott, J.; Snape, I.

    2009-04-01

    An overview of a recently published review of the scientific literature from the past decade on the impacts of human activities on the Antarctic environment is presented. An assessment of the cumulative effects of scientists and accompanying base construction, tourists and fishery activities in Antarctica is timely given a decade since the Protocol on Environmental Protection to the Antarctic Treaty came into force in 1998 and the increasing attention given to and human presence in Antarctica during this 2007-2009 IPY. A range of impacts has been identified at a variety of spatial and temporal scales. Chemical contamination and sewage disposal on the continent have been found to be long-lived, with contemporary sewage management practices at many coastal stations insufficient to prevent local contamination. Human activities, particularly construction and transport, have affected Antarctic flora and fauna and a small number of non-indigenous plant and animal species has become established on some of the Antarctic Peninsula and sub Antarctic islands. There is little indication of recovery of overexploited fish stocks, and ramifications of fishing activity on bycatch species and the ecosystem could also be far-reaching. The Antarctic Treaty System and its instruments, in particular the Convention for the Conservation of Antarctic Marine Living Resources (CCAMLR) and the Environmental Protocol, provide a framework within which management of human activities take place. In order to ensure comprehensive protection of the Antarctic environment, including its intrinsic, wilderness and scientific values in the face of the continuing expansion of human activities in Antarctica, a more effective implementation of a wide range of measures is essential. These include effective environmental impact assessments, long-term monitoring, mitigation measures for non-indigenous species, ecosystem-based management of living resources, and increased regulation of National Antarctic

  1. Structural heterogeneity regarding local Shwartzman activity of lipid A.

    PubMed

    Mashimo, J; Tanaka, C; Arata, S; Akiyama, Y; Hata, S; Hirayama, T; Egawa, K; Kasai, N

    1988-01-01

    The relation of chemical structure to local Shwartzman activity of lipid A preparations purified by thin-layer chromatography from five bacterial strains was examined. Two lipid A fractions from E. coli F515--Ec-A2 and Ec-A3--exhibited strong activity, similar to that of previous synthetic E. coli-type lipid A (compound 506 or LA-15-PP). The Ec-A3 fraction contained a component that appeared to be structurally identical to compound 506, and the main component of Ec-A2 fraction was structurally similar to compound 506 except that it carried a 3-hydroxytetradecanoyl group at the C-3' position of the backbone in place of a 3-tetradecanoyloxytetradecanoyl group. Free lipid A (12 C) and purified lipid A fractions, Ec-A2 (12 C) and Ec-A3 (12 C), respectively, obtained from bacteria grown at 12 C, exhibited activity comparable to Ec-A2 or Ec-A3. In these preparations, a large part of the 3-dodecanoyloxytetradecanoyl group might be replaced by 3-hexadecenoyloxytetradecanoyl group. Salmonella minnesota R595 free lipid A also contained at least two active lipid A components as seen in E. coli lipid A, but the third component corresponding to the synthetic Salmonella-type lipid A (compound 516 or LA-16-PP) exhibited low activity. A lipid A fraction, Cv-A4 from Chromobacterium violaceum IFO 12614, which was proposed to have two acyloxyacyl groups at the C-2 and C-2' positions with other acyl groups, exhibited weaker activity than the free lipid A or LPS. The purified lipid A fractions from Pseudomonas diminuta JCM 2788 and Pseudomonas vesicularis JCM 1477 contained an unusual backbone with 2,3-diamino-2,3-dideoxy-D-glucose disaccharide phosphomonoester, and these lipid A (Pd-A3 and Pv-A3) exhibited strong activity comparable to the E. coli lipid A. Thus, the present results show that the local Shwartzman reaction can be expressed by partly different lipid A structures in both hydrophilic backbone and fatty acyl residues; when they have the same backbone the potency varies

  2. Spin dynamics under local gauge fields in chiral spin-orbit coupling systems

    NASA Astrophysics Data System (ADS)

    Tan, S. G.; Jalil, M. B. A.; Fujita, T.; Liu, X. J.

    2011-02-01

    We present a theoretical description of local spin dynamics in magnetic systems with a chiral spin texture and finite spin-orbit coupling (SOC). Spin precession about the relativistic effective magnetic field in a SOC system gives rise to a non-Abelian SU(2) gauge field reminiscent of the Yang-Mills field. In addition, the adiabatic relaxation of electron spin along the local spin yields an U(1) ⊗ U(1) topological gauge (Berry) field. We derive the corresponding equation of motion i.e. modified Landau-Lifshitz-Gilbert (LLG) equation, for the local spin under the influence of these effects. Focusing on the SU(2) gauge, we obtain the spin torque magnitude, and the amplitude and frequency of spin oscillations in this system. Our theoretical estimates indicate significant spin torque and oscillations in systems with large spin-orbit coupling, which may be utilized in technological applications such as current-induced magnetization-switching and tunable microwave oscillators.

  3. Determining the True Polarity and Amplitude of Synaptic Currents Underlying Gamma Oscillations of Local Field Potentials

    PubMed Central

    Makarov, Valeri A.; Herreras, Oscar

    2013-01-01

    Fluctuations in successive waves of oscillatory local field potentials (LFPs) reflect the ongoing processing of neuron populations. However, their amplitude, polarity and synaptic origin are uncertain due to the blending of electric fields produced by multiple converging inputs, and the lack of a baseline in standard AC-coupled recordings. Consequently, the estimation of underlying currents by laminar analysis yields spurious sequences of inward and outward currents. We devised a combined analytical/experimental approach that is suitable to study laminated structures. The approach was essayed on an experimental oscillatory LFP as the Schaffer-CA1 gamma input in anesthetized rats, and it was verified by parallel processing of model LFPs obtained through a realistic CA1 aggregate of compartmental units. This approach requires laminar LFP recordings and the isolation of the oscillatory input from other converging pathways, which was achieved through an independent component analysis. It also allows the spatial and temporal components of pathway-specific LFPs to be separated. While reconstructed Schaffer-specific LFPs still show spurious inward/outward current sequences, these were clearly stratified into distinct subcellular domains. These spatial bands guided the localized delivery of neurotransmitter blockers in experiments. As expected, only Glutamate but not GABA blockers abolished Schaffer LFPs when applied to the active but not passive subcellular domains of pyramidal cells. The known chemical nature of the oscillatory LFP allowed an empirical offset of the temporal component of Schaffer LFPs, such that following reconstruction they yield only sinks or sources at the appropriate sites. In terms of number and polarity, some waves increased and others decreased proportional to the concomitant inputs in native multisynaptic LFPs. Interestingly, the processing also retrieved the initiation time for each wave, which can be used to discriminate afferent from

  4. Prediction of STN-DBS Electrode Implantation Track in Parkinson's Disease by Using Local Field Potentials.

    PubMed

    Telkes, Ilknur; Jimenez-Shahed, Joohi; Viswanathan, Ashwin; Abosch, Aviva; Ince, Nuri F

    2016-01-01

    Optimal electrophysiological placement of the DBS electrode may lead to better long term clinical outcomes. Inter-subject anatomical variability and limitations in stereotaxic neuroimaging increase the complexity of physiological mapping performed in the operating room. Microelectrode single unit neuronal recording remains the most common intraoperative mapping technique, but requires significant expertise and is fraught by potential technical difficulties including robust measurement of the signal. In contrast, local field potentials (LFPs), owing to their oscillatory and robust nature and being more correlated with the disease symptoms, can overcome these technical issues. Therefore, we hypothesized that multiple spectral features extracted from microelectrode-recorded LFPs could be used to automate the identification of the optimal track and the STN localization. In this regard, we recorded LFPs from microelectrodes in three tracks from 22 patients during DBS electrode implantation surgery at different depths and aimed to predict the track selected by the neurosurgeon based on the interpretation of single unit recordings. A least mean square (LMS) algorithm was used to de-correlate LFPs in each track, in order to remove common activity between channels and increase their spatial specificity. Subband power in the beta band (11-32 Hz) and high frequency range (200-450 Hz) were extracted from the de-correlated LFP data and used as features. A linear discriminant analysis (LDA) method was applied both for the localization of the dorsal border of STN and the prediction of the optimal track. By fusing the information from these low and high frequency bands, the dorsal border of STN was localized with a root mean square (RMS) error of 1.22 mm. The prediction accuracy for the optimal track was 80%. Individual beta band (11-32 Hz) and the range of high frequency oscillations (200-450 Hz) provided prediction accuracies of 72 and 68% respectively. The best prediction

  5. Prediction of STN-DBS Electrode Implantation Track in Parkinson's Disease by Using Local Field Potentials

    PubMed Central

    Telkes, Ilknur; Jimenez-Shahed, Joohi; Viswanathan, Ashwin; Abosch, Aviva; Ince, Nuri F.

    2016-01-01

    Optimal electrophysiological placement of the DBS electrode may lead to better long term clinical outcomes. Inter-subject anatomical variability and limitations in stereotaxic neuroimaging increase the complexity of physiological mapping performed in the operating room. Microelectrode single unit neuronal recording remains the most common intraoperative mapping technique, but requires significant expertise and is fraught by potential technical difficulties including robust measurement of the signal. In contrast, local field potentials (LFPs), owing to their oscillatory and robust nature and being more correlated with the disease symptoms, can overcome these technical issues. Therefore, we hypothesized that multiple spectral features extracted from microelectrode-recorded LFPs could be used to automate the identification of the optimal track and the STN localization. In this regard, we recorded LFPs from microelectrodes in three tracks from 22 patients during DBS electrode implantation surgery at different depths and aimed to predict the track selected by the neurosurgeon based on the interpretation of single unit recordings. A least mean square (LMS) algorithm was used to de-correlate LFPs in each track, in order to remove common activity between channels and increase their spatial specificity. Subband power in the beta band (11–32 Hz) and high frequency range (200–450 Hz) were extracted from the de-correlated LFP data and used as features. A linear discriminant analysis (LDA) method was applied both for the localization of the dorsal border of STN and the prediction of the optimal track. By fusing the information from these low and high frequency bands, the dorsal border of STN was localized with a root mean square (RMS) error of 1.22 mm. The prediction accuracy for the optimal track was 80%. Individual beta band (11–32 Hz) and the range of high frequency oscillations (200–450 Hz) provided prediction accuracies of 72 and 68% respectively. The best

  6. Local time resolved dynamics of field-aligned currents and their response to solar wind variability

    NASA Astrophysics Data System (ADS)

    He, Maosheng; Vogt, Joachim; Lühr, Hermann; Sorbalo, Eugen

    2014-07-01

    Using 10 years of CHAMP measurements condensed into the empirical model of field-aligned currents through empirical orthogonal function analysis, the dynamics of field-aligned currents (FACs) is modeled and studied in separate magnetic local time (MLT) sectors. We investigate the distributions of FAC intensity and latitude and evaluate their predictability in terms of geospace parameters which are ranked according to their relative importance measured by a multivariate regression procedure. The response time to changes in solar wind variables is studied in detail and found to be much shorter for dayside FACs than on the nightside (15-25 min versus 35-95 min). Furthermore, dayside FACs can be parameterized more accurately: R2 values maximize greater than 0.7 for FAC latitude and greater than 0.3 for FAC intensity, whereas the corresponding values on the nightside are smaller than 0.3 and 0.15, respectively. The results support the separation between directly driven coupling processes acting on the dayside and unloading processes controlling the nightside. In addition, the MLT-resolved standardized regression coefficients suggest that (1) FAC latitude is affected most significantly by the transpolar potential, substorm evolution, solar activity as represented by the F10.7 index and its square, and the dipole tilt; (2) Region-1/2 current intensity is controlled most efficiently by substorm evolution, IMF Bz and IMF By; and (3) cusp current intensity is influenced by conductivity, IMF By and their cross item.

  7. Localization and quasilocalization of a spin-1 /2 fermion field on a two-field thick braneworld

    NASA Astrophysics Data System (ADS)

    Guo, Heng; Xie, Qun-Ying; Fu, Chun-E.

    2015-11-01

    Localization of a spin-1 /2 fermion on the braneworld is an important and interesting problem. It is well known that a five-dimensional free massless fermion Ψ minimally coupled to gravity cannot be localized on the Randall-Sundrum braneworld. In order to trap such a fermion, the coupling between the fermion and bulk scalar fields should be introduced. In this paper, localization and quasilocalization of a bulk fermion on the thick braneworld generated by two scalar fields (a kink scalar ϕ and a dilaton scalar π ) are investigated. Two types of couplings between the fermion and two scalars are considered. One coupling is the usual Yukawa coupling -η Ψ ¯ϕ Ψ between the fermion and kink scalar, another one is λ Ψ ¯ΓM∂Mπ γ5Ψ between the fermion and dilaton scalar. The left-chiral fermion zero mode can be localized on the brane, and both the left- and right-chiral fermion massive Kaluza-Klein modes may be localized or quasilocalized. Hence the four-dimensional massless left-chiral fermion and massive Dirac fermions, whose lifetime is infinite or finite, can be obtained on the brane.

  8. A method to localize RF B₁ field in high-field magnetic resonance imaging systems.

    PubMed

    Yoo, Hyoungsuk; Gopinath, Anand; Vaughan, J Thomas

    2012-12-01

    In high-field magnetic resonance imaging (MRI) systems, B₀ fields of 7 and 9.4 T, the RF field shows greater inhomogeneity compared to clinical MRI systems with B₀ fields of 1.5 and 3.0 T. In multichannel RF coils, the magnitude and phase of the input to each coil element can be controlled independently to reduce the nonuniformity of the RF field. The convex optimization technique has been used to obtain the optimum excitation parameters with iterative solutions for homogeneity in a selected region of interest. The pseudoinverse method has also been used to find a solution. The simulation results for 9.4- and 7-T MRI systems are discussed in detail for the head model. Variation of the simulation results in a 9.4-T system with the number of RF coil elements for different positions of the regions of interest in a spherical phantom are also discussed. Experimental results were obtained in a phantom in the 9.4-T system and are compared to the simulation results and the specific absorption rate has been evaluated. PMID:22929360

  9. Modulation of local field potential power of the subthalamic nucleus during isometric force generation in patients with Parkinson's disease.

    PubMed

    Florin, E; Dafsari, H S; Reck, C; Barbe, M T; Pauls, K A M; Maarouf, M; Sturm, V; Fink, G R; Timmermann, L

    2013-06-14

    Investigations of local field potentials of the subthalamic nucleus of patients with Parkinson's disease have provided evidence for pathologically exaggerated oscillatory beta-band activity (13-30 Hz) which is amenable to physiological modulation by, e.g., voluntary movement. Previous functional magnetic resonance imaging studies in healthy controls have provided evidence for an increase of subthalamic nucleus blood-oxygenation-level-dependant signal in incremental force generation tasks. However, the modulation of neuronal activity by force generation and its relationship to peripheral feedback remain to be elucidated. We hypothesised that beta-band activity in the subthalamic nucleus is modulated by incremental force generation. Subthalamic nucleus local field potentials were recorded intraoperatively in 13 patients with Parkinson's disease (37 recording sites) during rest and five incremental isometric force generation conditions of the arm with applied loads of 0-400 g (in 100-g increments). Repeated measures analysis of variance (ANOVA) revealed a modulation of local field potential (LFP) power in the upper beta-band (in 24-30 Hz; F(₃.₀₄₂)=4.693, p=0.036) and the gamma-band (in 70-76 Hz; F(₄)=4.116, p=0.036). Granger-causality was computed with the squared partial directed coherence and showed no significant modulation during incremental isometric force generation. Our findings indicate that the upper beta- and gamma-band power of subthalamic nucleus local field potentials are modulated by the physiological task of force generation in patients with Parkinson's disease. This modulation seems to be not an effect of a modulation of peripheral feedback. PMID:23454540

  10. Ketamine Alters Outcome-Related Local Field Potentials in Monkey Prefrontal Cortex.

    PubMed

    Skoblenick, Kevin J; Womelsdorf, Thilo; Everling, Stefan

    2016-06-01

    A subanesthetic dose of the noncompetitive N-methyl-d-aspartate receptor antagonist ketamine is known to induce a schizophrenia-like phenotype in humans and nonhuman primates alike. The transient behavioral changes mimic the positive, negative, and cognitive symptoms of the disease but the neural mechanisms behind these changes are poorly understood. A growing body of evidence indicates that the cognitive control processes associated with prefrontal cortex (PFC) regions relies on groups of neurons synchronizing at narrow-band frequencies measurable in the local field potential (LFP). Here, we recorded LFPs from the caudo-lateral PFC of 2 macaque monkeys performing an antisaccade task, which requires the suppression of an automatic saccade toward a stimulus and the initiation of a goal-directed saccade in the opposite direction. Preketamine injection activity showed significant differences in a narrow 20-30 Hz beta frequency band between correct and error trials in the postsaccade response epoch. Ketamine significantly impaired the animals' performance and was associated with a loss of the differences in outcome-specific beta-band power. Instead, we observed a large increase in high-gamma-band activity. Our results suggest that the PFC employs beta-band synchronization to prepare for top-down cognitive control of saccades and the monitoring of task outcome. PMID:26045564

  11. Nociceptive Local Field Potentials Recorded from the Human Insula Are Not Specific for Nociception

    PubMed Central

    Liberati, Giulia; Klöcker, Anne; Safronova, Marta M.; Ferrão Santos, Susana; Ribeiro Vaz, Jose-Geraldo; Raftopoulos, Christian; Mouraux, André

    2016-01-01

    The insula, particularly its posterior portion, is often regarded as a primary cortex for pain. However, this interpretation is largely based on reverse inference, and a specific involvement of the insula in pain has never been demonstrated. Taking advantage of the high spatiotemporal resolution of direct intracerebral recordings, we investigated whether the human insula exhibits local field potentials (LFPs) specific for pain. Forty-seven insular sites were investigated. Participants received brief stimuli belonging to four different modalities (nociceptive, vibrotactile, auditory, and visual). Both nociceptive stimuli and non-nociceptive vibrotactile, auditory, and visual stimuli elicited consistent LFPs in the posterior and anterior insula, with matching spatial distributions. Furthermore, a blind source separation procedure showed that nociceptive LFPs are largely explained by multimodal neural activity also contributing to non-nociceptive LFPs. By revealing that LFPs elicited by nociceptive stimuli reflect activity unrelated to nociception and pain, our results confute the widespread assumption that these brain responses are a signature for pain perception and its modulation. PMID:26734726

  12. Direct mapping of local director field of nematic liquid crystals at the nano-scale

    NASA Astrophysics Data System (ADS)

    Xia, Yu; Serra, Francesca; Yang, Shu; Kamien, Randall

    2015-03-01

    The director field in liquid crystals (LCs) has been characterized mainly via polarized optical microscopy, fluorescence confocal microscopy, and Raman spectroscopy, all of which are limited by optical wavelengths - from hundreds of nanometers to several micrometers. Since LC orientation cannot be resolved directly by these methods, theory is needed to interpret the local director field of LC alignment. In this work, we introduce a new approach to directly visualize the local director field of a nematic LC (NLC) at the nano-scale using scanning electron microscopy (SEM). A new type of NLC monomer bearing crosslinkable groups was designed and synthesized. It can be well-oriented at particle surfaces and patterned polymer substrates, including micron-sized silica colloids, porous membranes, micropillar arrays, and 1D channels. After carefully crosslinking, the molecular orientation of NLCs around the particles or within the patterns could be directly visualized by SEM, showing oriented nanofibers representing LC director from the fractured samples. Here, we could precisely resolve not only the local director field by this approach, but the defect structures of NLCs, including hedgehogs and line defects. The direct mapping of LC directors at the nanoscale using this method will improve our understanding of NLC local director field, and thus their manipulation and applications. More importantly, a theoretical interpretation will no longer be a necessity to resolve a new material system in this field.

  13. Lorentz factor determination for local electric fields in semiconductor devices utilizing hyper-thin dielectrics

    SciTech Connect

    McPherson, J. W.

    2015-11-28

    The local electric field (the field that distorts, polarizes, and weakens polar molecular bonds in dielectrics) has been investigated for hyper-thin dielectrics. Hyper-thin dielectrics are currently required for advanced semiconductor devices. In the work presented, it is shown that the common practice of using a Lorentz factor of L = 1/3, to describe the local electric field in a dielectric layer, remains valid for hyper-thin dielectrics. However, at the very edge of device structures, a rise in the macroscopic/Maxwell electric field E{sub diel} occurs and this causes a sharp rise in the effective Lorentz factor L{sub eff}. At capacitor and transistor edges, L{sub eff} is found to increase to a value 2/3 < L{sub eff} < 1. The increase in L{sub eff} results in a local electric field, at device edge, that is 50%–100% greater than in the bulk of the dielectric. This increase in local electric field serves to weaken polar bonds thus making them more susceptible to breakage by standard Boltzmann and/or current-driven processes. This has important time-dependent dielectric breakdown (TDDB) implications for all electronic devices utilizing polar materials, including GaN devices that suffer from device-edge TDDB.

  14. Local high-resolution crustal magnetic field analysis from satellite data

    NASA Astrophysics Data System (ADS)

    Plattner, Alain; Simons, Frederik J.

    2016-04-01

    Planetary crustal magnetic fields are key to understanding a planet or moon's structure and history. Due to satellite orbit parameters such as aerobraking (Mars) or only partial coverage (Mercury), or simply because of the strongly heterogeneous crustal field strength, satellite data of planetary magnetic fields vary regionally in their signal-to noise ratio and data coverage. To take full advantage of data quality within one region of a planet or moon without diluting the data with lower quality measurements outside of that region we resort to local methods. Slepian functions are linear combinations of spherical harmonics that provide local sensitivity to structure. Here we present a selection of crustal magnetic field models obtained from vector-valued variable-altitude satellite observations using an altitude-cognizant gradient-vector Slepian approach. This method is based on locally maximizing energy concentration within the region of data availability while simultaneously bandlimiting the model in terms of its spherical-harmonic degree and minimizing noise amplification due to downward continuation. For simple regions such as spherical caps, our method is computationally efficient and allows us to calculate local crustal magnetic field solutions beyond spherical harmonic degree 800, if the data permit. We furthermore discuss extensions of the method that are optimized for the analysis and separation of internal and external magnetic fields.

  15. Effects of the local structure dependence of evaporation fields on field evaporation behavior

    SciTech Connect

    Yao, Lan; Marquis, Emmanuelle A.; Withrow, Travis; Restrepo, Oscar D.; Windl, Wolfgang

    2015-12-14

    Accurate three dimensional reconstructions of atomic positions and full quantification of the information contained in atom probe microscopy data rely on understanding the physical processes taking place during field evaporation of atoms from needle-shaped specimens. However, the modeling framework for atom probe microscopy has only limited quantitative justification. Building on the continuum field models previously developed, we introduce a more physical approach with the selection of evaporation events based on density functional theory calculations. This model reproduces key features observed experimentally in terms of sequence of evaporation, evaporation maps, and depth resolution, and provides insights into the physical limit for spatial resolution.

  16. The Evolution of the Physical Activity Field

    ERIC Educational Resources Information Center

    Blair, Steven N.; Powell, Kenneth E.

    2014-01-01

    This article includes an historical review of research on physical activity and health, and how the findings have contributed to physical activity participation and promotion today. In the 20th century, research began to accumulate on the effects of exercise on physiological functions, and later on the relation between regular activity and various…

  17. Microfluidic Platform Generates Oxygen Landscapes for Localized Hypoxic Activation

    PubMed Central

    Rexius, Megan L.; Mauleon, Gerardo; Malik, Asrar B.; Rehman, Jalees; Eddington, David T.

    2014-01-01

    An open-well microfluidic platform generates an oxygen landscape using gas-perfused networks which diffuse across a membrane. The device enables real-time analysis of cellular and tissue responses to oxygen tension to define how cells adapt to heterogeneous oxygen conditions found in the physiological setting. We demonstrate that localized hypoxic activation of cells elicited specific metabolic and gene responses in human microvascular endothelial cells and bone marrow-derived mesenchymal stem cells. A robust demonstration of the compatibility of the device with standard laboratory techniques demonstrates the wide utility of the method. This platform is ideally suited to study real-time cell responses and cell-cell interactions within physiologically relevant oxygen landscapes. PMID:25315003

  18. Field localization and enhancement near the Dirac point of a finite defectless photonic crystal

    NASA Astrophysics Data System (ADS)

    D'Aguanno, Giuseppe; Mattiucci, Nadia; Conti, Claudio; Bloemer, Mark J.

    2013-02-01

    We use a rigorous electromagnetic approach to show the existence of strongly localized modes in the stop band of a linear, two-dimensional, finite photonic crystal near its Dirac point. At normal incidence, the crystal exhibits a Dirac point with 100% transmission. At angles slightly off the normal, where the crystal is 100% reflective, instead of exponentially decaying fields as in a photonic stop band, the field becomes strongly localized and enhanced inside the crystal. We explain that this anomalous localization is due to guided mode resonances that are the foundation of the Dirac point itself and also shape its adjacent band gap. Besides shedding new light on the physical origin of Dirac points in finite photonic crystals, our results could have applications in many nonlinear light-matter interaction phenomena in which it is crucial to achieve a high degree of light localization.

  19. Localization-based full-field microscopy: how to attain super-resolved images

    PubMed Central

    Son, Taehwang; Lee, Wonju; Kim, Donghyun

    2015-01-01

    In this study, we have investigated localization-based microscopy to achieve full-field super-resolution. For localized sampling, we have considered combs consisting of unit pulses and near-fields localized by surface nanoapertures. Achievable images after reconstruction were assessed in terms of peak signal-to-noise ratio (PSNR). It was found that spatial switching of individual pulses may be needed to break the diffraction limit. Among the parameters, the resolution was largely determined by sampling period while the effect of width of a sampling pulse on PSNR was relatively limited. For the range of sampling parameters that we considered, the highest resolution achievable is estimated to be 70 nm, which can further be enhanced by optimizing the localization parameters. PMID:26201451

  20. Using stress shadows to invert for changes in local stress field

    NASA Astrophysics Data System (ADS)

    Latimer, C. D.; Tiampo, K. F.; Rundle, J.

    2009-12-01

    When a large earthquake occurs, stresses in the crust are redistributed creating regions that experience an increase in stress while others experience a stress decrease which are called stress shadows. In many studies, these stress shadows are said to contain less seismic activity than the average background rate, and so correlations are made between lack of seismicity or a decrease in seismicity rate and the stress shadow locations and magnitudes (the amount of decrease of stress). In this study the opposite procedure is applied: We use seismicity rate changes to determine information about the stress changes due to a large magnitude earthquake, as well as its effect on the stress field itself. We use the Pattern Informatics method to examine the changes in seismicity rate, as it is an objective measure of the rate changes with respect to the regional background rate. The results from this analysis are then used to invert for, with a genetic algorithm, parameters that define the stress field such as the principal stress orientations, the coefficient of friction, and the calculation depth. The modelled stress data is calculated using Coulomb stress change theory and the Coulomb 3 program, and it is trying to produce the same size and location of stress shadows as seen in the seismicity rate change data. Four different Californian earthquakes were chosen in order to determine their effect on the local stress field: (1) 1987 Superstition Hills (2) 1989 Loma Prieta (3) 1992 Landers and (4) 1994 Northridge. In order to find out the effect that each of the parameters have on the modelled results, we performed a Monte Carlo simulation to find the errors associated with each, and a sensitivity analysis to determine the magnitude of change that each one produces. We hope with this new information of the changes incurred due to a large magnitude earthquake occurrence, that modelling of earthquakes can be advanced, and our understanding of their mechanics enhanced.

  1. A Model of the Medial Superior Olive Explains Spatiotemporal Features of Local Field Potentials

    PubMed Central

    Mc Laughlin, Myles; Verschooten, Eric; Joris, Philip X.; Rinzel, John

    2014-01-01

    Local field potentials are important indicators of in vivo neural activity. Sustained, phase-locked, sound-evoked extracellular fields in the mammalian auditory brainstem, known as the auditory neurophonic, reflect the activity of neurons in the medial superior olive (MSO). We develop a biophysically based model of the neurophonic that accounts for features of in vivo extracellular recordings in the cat auditory brainstem. By making plausible idealizations regarding the spatial symmetry of MSO neurons and the temporal synchrony of their afferent inputs, we reduce the challenging problem of computing extracellular potentials in a 3D volume conductor to a one-dimensional problem. We find that postsynaptic currents in bipolar MSO neuron models generate extracellular voltage responses that strikingly resemble in vivo recordings. Simulations reproduce distinctive spatiotemporal features of the in vivo neurophonic response to monaural pure tones: large oscillations (hundreds of microvolts to millivolts), broad spatial reach (millimeter scale), and a dipole-like spatial profile. We also explain how somatic inhibition and the relative timing of bilateral excitation may shape the spatial profile of the neurophonic. We observe in simulations, and find supporting evidence in in vivo data, that coincident excitatory inputs on both dendrites lead to a drastically reduced spatial reach of the neurophonic. This outcome surprises because coincident inputs are thought to evoke maximal firing rates in MSO neurons, and it reconciles previously puzzling evoked potential results in humans and animals. The success of our model, which has no axon or spike-generating sodium currents, suggests that MSO spikes do not contribute appreciably to the neurophonic. PMID:25164666

  2. A model of the medial superior olive explains spatiotemporal features of local field potentials.

    PubMed

    Goldwyn, Joshua H; Mc Laughlin, Myles; Verschooten, Eric; Joris, Philip X; Rinzel, John

    2014-08-27

    Local field potentials are important indicators of in vivo neural activity. Sustained, phase-locked, sound-evoked extracellular fields in the mammalian auditory brainstem, known as the auditory neurophonic, reflect the activity of neurons in the medial superior olive (MSO). We develop a biophysically based model of the neurophonic that accounts for features of in vivo extracellular recordings in the cat auditory brainstem. By making plausible idealizations regarding the spatial symmetry of MSO neurons and the temporal synchrony of their afferent inputs, we reduce the challenging problem of computing extracellular potentials in a 3D volume conductor to a one-dimensional problem. We find that postsynaptic currents in bipolar MSO neuron models generate extracellular voltage responses that strikingly resemble in vivo recordings. Simulations reproduce distinctive spatiotemporal features of the in vivo neurophonic response to monaural pure tones: large oscillations (hundreds of microvolts to millivolts), broad spatial reach (millimeter scale), and a dipole-like spatial profile. We also explain how somatic inhibition and the relative timing of bilateral excitation may shape the spatial profile of the neurophonic. We observe in simulations, and find supporting evidence in in vivo data, that coincident excitatory inputs on both dendrites lead to a drastically reduced spatial reach of the neurophonic. This outcome surprises because coincident inputs are thought to evoke maximal firing rates in MSO neurons, and it reconciles previously puzzling evoked potential results in humans and animals. The success of our model, which has no axon or spike-generating sodium currents, suggests that MSO spikes do not contribute appreciably to the neurophonic. PMID:25164666

  3. 63,65Cu NMR Method in a Local Field for Investigation of Copper Ore Concentrates

    NASA Astrophysics Data System (ADS)

    Gavrilenko, A. N.; Starykh, R. V.; Khabibullin, I. Kh.; Matukhin, V. L.

    2015-01-01

    To choose the most efficient method and ore beneficiation flow diagram, it is important to know physical and chemical properties of ore concentrates. The feasibility of application of the 63,65Cu nuclear magnetic resonance (NMR) method in a local field aimed at studying the properties of copper ore concentrates in the copper-iron-sulfur system is demonstrated. 63,65Cu NMR spectrum is measured in a local field for a copper concentrate sample and relaxation parameters (times T1 and T2) are obtained. The spectrum obtained was used to identify a mineral (chalcopyrite) contained in the concentrate. Based on the experimental data, comparative characteristics of natural chalcopyrite and beneficiated copper concentrate are given. The feasibility of application of the NMR method in a local field to explore mineral deposits is analyzed.

  4. The effects of the local environment on active galactic nuclei

    SciTech Connect

    Manzer, L. H.; De Robertis, M. M. E-mail: mmdr@yorku.ca

    2014-06-20

    There continues to be significant controversy regarding the mechanism(s) responsible for the initiation and maintenance of activity in galactic nuclei. In this paper we will investigate possible environmental triggers of nuclear activity through a statistical analysis of a large sample of galaxy groups. The focus of this paper is to identify active galactic nuclei (AGNs) and other emission-line galaxies in these groups and to compare their frequency with a sample of over 260,000 isolated galaxies from the same catalog. The galaxy groups are taken from the catalog of Yang et al., in which over 20,000 virialized groups of galaxies (2 ≤ N ≤ 20) with redshifts between 0.01 and 0.20 are from the Sloan Digital Sky Survey. We first investigate the completeness of our data set and find, though biases are a concern particularly at higher redshift, that our data provide a fair representation of the local universe. After correcting emission-line equivalent widths for extinction and underlying Balmer stellar absorption, we classify galaxies in the sample using traditional emission-line ratios, while incorporating measurement uncertainties. We find a significantly higher fraction of AGNs in groups compared with the isolated sample. Likewise, a significantly higher fraction of absorption-line galaxies are found in groups, while a higher fraction of star-forming galaxies prefer isolated environments. Within grouped environments, AGNs and star-forming galaxies are found more frequently in small- to medium-richness groups, while absorption-line galaxies prefer groups with larger richnesses. Groups containing only emission-line galaxies have smaller virial radii, velocity dispersions, and masses compared with those containing only absorption-line galaxies. Furthermore, the AGN fraction increases with decreasing distance to the group centroid, independent of galaxy morphology. Using properties obtained from Galaxy Zoo, there is an increased fraction of AGNs within merging systems

  5. Instantaneous spatially local projective measurements are consistent in a relativistic quantum field

    SciTech Connect

    Lin, Shih-Yuin

    2012-12-15

    Suppose the postulate of measurement in quantum mechanics can be extended to quantum field theory; then a local projective measurement at some moment on an object locally coupled with a relativistic quantum field will result in a projection or collapse of the wavefunctional of the combined system defined on the whole time-slice associated with the very moment of the measurement, if the relevant degrees of freedom have nonzero correlations. This implies that the wavefunctionals in the same Hamiltonian system but defined in different reference frames would collapse on different time-slices passing through the same local event where the measurement was done. Are these post-measurement states consistent with each other? We illustrate that the quantum states of the Raine-Sciama-Grove detector-field system started with the same initial Gaussian state defined on the same initial time-slice, then collapsed by the measurements on the pointlike detectors on different time-slices in different frames, will evolve to the same state of the combined system up to a coordinate transformation when compared on the same final time-slice. Such consistency is guaranteed by the spatial locality of interactions and the general covariance in a relativistic system, together with the spatial locality of measurements and the linearity of quantum dynamics in its quantum theory. - Highlights: Black-Right-Pointing-Pointer Spatially local quantum measurements in detector-field models are studied. Black-Right-Pointing-Pointer Local quantum measurement collapses the wavefunctional on the whole time-slice. Black-Right-Pointing-Pointer In different frames wavefunctionals of a field would collapse on different time-slices. Black-Right-Pointing-Pointer States collapsed by the same measurement will be consistent on the same final slice.

  6. Far-ultraviolet studies. VII - The spectrum and latitude dependence of the local interstellar radiation field

    NASA Technical Reports Server (NTRS)

    Henry, R. C.; Anderson, R. C.; Fastie, W. G.

    1980-01-01

    A direct measurement has been made of the spectrum (1180-1680 A) and Gould-latitude dependence of the local interstellar radiation field, over about one-third of the sky. The result is corrected to give expected values for the entire sky. The average local 1180-1680 A energy density is 5.8 x 10 to the -17th ergs/cu cm A. The surface brightness falls off toward high latitudes much more steeply than published models predict.

  7. Antifungal activity of the local complement system in cerebral aspergillosis.

    PubMed

    Rambach, Günter; Hagleitner, Magdalena; Mohsenipour, Iradj; Lass-Flörl, Cornelia; Maier, Hans; Würzner, Reinhard; Dierich, Manfred P; Speth, Cornelia

    2005-10-01

    Dissemination of aspergillosis into the central nervous system is associated with nearly 100% mortality. To study the reasons for the antifungal immune failure we analyzed the efficacy of cerebral complement to combat the fungus Aspergillus. Incubation of Aspergillus in non-inflammatory cerebrospinal fluid (CSF) revealed that complement levels were sufficient to obtain a deposition on the surface, but opsonization was much weaker than in serum. Consequently complement deposition from normal CSF on fungal surface stimulated a very low phagocytic activity of microglia, granulocytes, monocytes and macrophages compared to stimulation by conidia opsonized in serum. Similarly, opsonization of Aspergillus by CSF was not sufficient to induce an oxidative burst in infiltrating granulocytes, whereas conidia opsonized in serum induced a clear respiratory signal. Thus, granulocytes were capable of considerably reducing the viability of serum-opsonized Aspergillus conidia, but not of conidia opsonized in CSF. The limited efficacy of antifungal attack by cerebral complement can be partly compensated by enhanced synthesis, leading to elevated complement concentrations in CSF derived from a patient with cerebral aspergillosis. This inflammatory CSF was able to induce (i) a higher complement deposition on the Aspergillus surface than non-inflammatory CSF, (ii) an accumulation of complement activation products and (iii) an increase in phagocytic and killing activity of infiltrating granulocytes. However, levels and efficacy of the serum-derived complement were not reached. These data indicate that low local complement synthesis and activation may represent a central reason for the insufficient antifungal defense in the brain and the high mortality rate of cerebral aspergillosis. PMID:16027023

  8. Local electric fields and molecular properties in heterogeneous environments through polarizable embedding.

    PubMed

    List, Nanna Holmgaard; Jensen, Hans Jørgen Aagaard; Kongsted, Jacob

    2016-04-21

    In spectroscopies, the local field experienced by a molecule embedded in an environment will be different from the externally applied electromagnetic field, and this difference may significantly alter the response and transition properties of the molecule. The polarizable embedding (PE) model has previously been developed to model the local field contribution stemming from the direct molecule-environment coupling of the electromagnetic response properties of molecules in solution as well as in heterogeneous environments, such as proteins. Here we present an extension of this approach to address the additional effective external field effect, i.e., the manifestations of the environment polarization induced by the external field, which allows for the calculation of properties defined in terms of the external field. Within a response framework, we report calculations of the one- and two-photon absorption (1PA and 2PA, respectively) properties of PRODAN-methanol clusters as well as the fluorescent protein DsRed. Our results demonstrate the necessity of accounting for both the dynamical reaction field and effective external field contributions to the local field in order to reproduce full quantum chemical reference calculations. For the lowest π→π* transition in DsRed, inclusion of effective external field effects gives rise to a 1.9- and 3.5-fold reduction in the 1PA and 2PA cross-sections, respectively. The effective external field is, however, strongly influenced by the heterogeneity of the protein matrix, and the resulting effect can lead to either screening or enhancement depending on the nature of the transition under consideration. PMID:27007060

  9. Reprint of : Spin polarization induced by an electric field in the presence of weak localization effects

    NASA Astrophysics Data System (ADS)

    Guerci, Daniele; Borge, Juan; Raimondi, Roberto

    2016-08-01

    We evaluate the spin polarization (Edelstein or inverse spin galvanic effect) and the spin Hall current induced by an applied electric field by including the weak localization corrections for a two-dimensional electron gas. We show that the weak localization effects yield logarithmic corrections to both the spin polarization conductivity relating the spin polarization and the electric field and to the spin Hall angle relating the spin and charge currents. The renormalization of both the spin polarization conductivity and the spin Hall angle combine to produce a zero correction to the total spin Hall conductivity as required by an exact identity. Suggestions for the experimental observation of the effect are given.

  10. Local energy decay of massive Dirac fields in the 5D Myers-Perry metric

    NASA Astrophysics Data System (ADS)

    Daudé, Thierry; Kamran, Niky

    2012-07-01

    We consider massive Dirac fields evolving in the exterior region of a five-dimensional Myers-Perry black hole and study their propagation properties. Our main result states that the local energy of such fields decays in a weak sense at late times. We obtain this result in two steps: first, using the separability of the Dirac equation, we prove the absence of a pure point spectrum for the corresponding Dirac operator; second, using a new form of the equation adapted to the local rotations of the black hole, we show by a Mourre theory argument that the spectrum is absolutely continuous. This leads directly to our main result.

  11. Benthic processes and coastal aquaculture: merging models and field data at a local scale

    NASA Astrophysics Data System (ADS)

    Brigolin, Daniele; Rabouille, Christophe; Bombled, Bruno; Colla, Silvia; Pastres, Roberto; Pranovi, Fabio

    2016-04-01

    Shellfish farming is regarded as an organic extractive aquaculture activity. However, the production of faeces and pseudofaeces, in fact, leads to a net transfer of organic matter from the water column to the surface sediment. This process, which is expected to locally affect the sediment biogeochemistry, may also cause relevant changes in coastal areas characterized by a high density of farms. In this paper, we present the result of a study recently carried out in the Gulf of Venice (northern Adriatic sea), combining mathematical modelling and field sampling efforts. The work aimed at using a longline mussel farm as an in-situ test-case for modelling the differences in soft sediments biogeochemical processes along a gradient of organic deposition. We used an existing integrated model, allowing to describe biogeochemical fluxes towards the mussel farm and to predict the extent of the deposition area underneath it. The model framework includes an individual-based population dynamic model of the Mediterranean mussel coupled with a Lagrangian deposition model and a 1D benthic model of early diagenesis. The work was articulated in 3 steps: 1) the integrated model allowed to simulate the downward fluxes of organic matter originated by the farm, and the extent of its deposition area; 2) based on the first model application, two stations were localized, at which sediment cores were collected during a field campaign, carried out in June 2015. Measurements included O2 and pH microprofiling, porosity and micro-porosity, Total Organic Carbon, and pore waters NH4, PO4, SO4, Alkalinity, and Dissolved Inorganic Carbon; 3) two distinct early diagenesis models were set-up, reproducing observed field data in the sampled cores. Observed oxygen microprofiles showed a different behavior underneath the farm with respect to the outside reference station. In particular, a remarkable decrease in the oxygen penetration depth, and an increase in the O2 influx calculated from the

  12. Deep-subwavelength imaging of both electric and magnetic localized optical fields by plasmonic campanile nanoantenna

    PubMed Central

    Caselli, Niccolò; La China, Federico; Bao, Wei; Riboli, Francesco; Gerardino, Annamaria; Li, Lianhe; Linfield, Edmund H.; Pagliano, Francesco; Fiore, Andrea; Schuck, P. James; Cabrini, Stefano; Weber-Bargioni, Alexander; Gurioli, Massimo; Intonti, Francesca

    2015-01-01

    Tailoring the electromagnetic field at the nanoscale has led to artificial materials exhibiting fascinating optical properties unavailable in naturally occurring substances. Besides having fundamental implications for classical and quantum optics, nanoscale metamaterials provide a platform for developing disruptive novel technologies, in which a combination of both the electric and magnetic radiation field components at optical frequencies is relevant to engineer the light-matter interaction. Thus, an experimental investigation of the spatial distribution of the photonic states at the nanoscale for both field components is of crucial importance. Here we experimentally demonstrate a concomitant deep-subwavelength near-field imaging of the electric and magnetic intensities of the optical modes localized in a photonic crystal nanocavity. We take advantage of the “campanile tip”, a plasmonic near-field probe that efficiently combines broadband field enhancement with strong far-field to near-field coupling. By exploiting the electric and magnetic polarizability components of the campanile tip along with the perturbation imaging method, we are able to map in a single measurement both the electric and magnetic localized near-field distributions. PMID:26045401

  13. Deep-subwavelength imaging of both electric and magnetic localized optical fields by plasmonic campanile nanoantenna

    SciTech Connect

    Caselli, Niccolò; La China, Federico; Bao, Wei; Riboli, Francesco; Gerardino, Annamaria; Li, Lianhe; Linfield, Edmund H.; Pagliano, Francesco; Fiore, Andrea; Schuck, P. James; Cabrini, Stefano; Weber-Bargioni, Alexander; Gurioli, Massimo; Intonti, Francesca

    2015-06-05

    Tailoring the electromagnetic field at the nanoscale has led to artificial materials exhibiting fascinating optical properties unavailable in naturally occurring substances. Besides having fundamental implications for classical and quantum optics, nanoscale metamaterials provide a platform for developing disruptive novel technologies, in which a combination of both the electric and magnetic radiation field components at optical frequencies is relevant to engineer the light-matter interaction. Thus, an experimental investigation of the spatial distribution of the photonic states at the nanoscale for both field components is of crucial importance. Here we experimentally demonstrate a concomitant deep-subwavelength near-field imaging of the electric and magnetic intensities of the optical modes localized in a photonic crystal nanocavity. We take advantage of the “campanile tip”, a plasmonic near-field probe that efficiently combines broadband field enhancement with strong far-field to near-field coupling. In conclusion, by exploiting the electric and magnetic polarizability components of the campanile tip along with the perturbation imaging method, we are able to map in a single measurement both the electric and magnetic localized near-field distributions.

  14. Deep-subwavelength imaging of both electric and magnetic localized optical fields by plasmonic campanile nanoantenna

    DOE PAGESBeta

    Caselli, Niccolò; La China, Federico; Bao, Wei; Riboli, Francesco; Gerardino, Annamaria; Li, Lianhe; Linfield, Edmund H.; Pagliano, Francesco; Fiore, Andrea; Schuck, P. James; et al

    2015-06-05

    Tailoring the electromagnetic field at the nanoscale has led to artificial materials exhibiting fascinating optical properties unavailable in naturally occurring substances. Besides having fundamental implications for classical and quantum optics, nanoscale metamaterials provide a platform for developing disruptive novel technologies, in which a combination of both the electric and magnetic radiation field components at optical frequencies is relevant to engineer the light-matter interaction. Thus, an experimental investigation of the spatial distribution of the photonic states at the nanoscale for both field components is of crucial importance. Here we experimentally demonstrate a concomitant deep-subwavelength near-field imaging of the electric and magneticmore » intensities of the optical modes localized in a photonic crystal nanocavity. We take advantage of the “campanile tip”, a plasmonic near-field probe that efficiently combines broadband field enhancement with strong far-field to near-field coupling. In conclusion, by exploiting the electric and magnetic polarizability components of the campanile tip along with the perturbation imaging method, we are able to map in a single measurement both the electric and magnetic localized near-field distributions.« less

  15. Deep-subwavelength imaging of both electric and magnetic localized optical fields by plasmonic campanile nanoantenna.

    PubMed

    Caselli, Niccolò; La China, Federico; Bao, Wei; Riboli, Francesco; Gerardino, Annamaria; Li, Lianhe; Linfield, Edmund H; Pagliano, Francesco; Fiore, Andrea; Schuck, P James; Cabrini, Stefano; Weber-Bargioni, Alexander; Gurioli, Massimo; Intonti, Francesca

    2015-01-01

    Tailoring the electromagnetic field at the nanoscale has led to artificial materials exhibiting fascinating optical properties unavailable in naturally occurring substances. Besides having fundamental implications for classical and quantum optics, nanoscale metamaterials provide a platform for developing disruptive novel technologies, in which a combination of both the electric and magnetic radiation field components at optical frequencies is relevant to engineer the light-matter interaction. Thus, an experimental investigation of the spatial distribution of the photonic states at the nanoscale for both field components is of crucial importance. Here we experimentally demonstrate a concomitant deep-subwavelength near-field imaging of the electric and magnetic intensities of the optical modes localized in a photonic crystal nanocavity. We take advantage of the "campanile tip", a plasmonic near-field probe that efficiently combines broadband field enhancement with strong far-field to near-field coupling. By exploiting the electric and magnetic polarizability components of the campanile tip along with the perturbation imaging method, we are able to map in a single measurement both the electric and magnetic localized near-field distributions. PMID:26045401

  16. Passive localization of mixed far-field and near-field sources without estimating the number of sources.

    PubMed

    Xie, Jian; Tao, Haihong; Rao, Xuan; Su, Jia

    2015-01-01

    This paper presents a novel algorithm for the localization of mixed far-field sources (FFSs) and near-field sources (NFSs) without estimating the source number. Firstly, the algorithm decouples the direction-of-arrival (DOA) estimation from the range estimation by exploiting fourth-order spatial-temporal cumulants of the observed data. Based on the joint diagonalization structure of multiple spatial-temporal cumulant matrices, a new one-dimensional (1-D) spatial spectrum function is derived to generate the DOA estimates of both FFSs and NFSs. Then, the FFSs and NFSs are identified and the range parameters of NFSs are determined via beamforming technique. Compared with traditional mixed sources localization algorithms, the proposed algorithm avoids the performance deterioration induced by erroneous source number estimation. Furthermore, it has a higher resolution capability and improves the estimation accuracy. Computer simulations are implemented to verify the effectiveness of the proposed algorithm. PMID:25668212

  17. Passive Localization of Mixed Far-Field and Near-Field Sources without Estimating the Number of Sources

    PubMed Central

    Xie, Jian; Tao, Haihong; Rao, Xuan; Su, Jia

    2015-01-01

    This paper presents a novel algorithm for the localization of mixed far-field sources (FFSs) and near-field sources (NFSs) without estimating the source number. Firstly, the algorithm decouples the direction-of-arrival (DOA) estimation from the range estimation by exploiting fourth-order spatial-temporal cumulants of the observed data. Based on the joint diagonalization structure of multiple spatial-temporal cumulant matrices, a new one-dimensional (1-D) spatial spectrum function is derived to generate the DOA estimates of both FFSs and NFSs. Then, the FFSs and NFSs are identified and the range parameters of NFSs are determined via beamforming technique. Compared with traditional mixed sources localization algorithms, the proposed algorithm avoids the performance deterioration induced by erroneous source number estimation. Furthermore, it has a higher resolution capability and improves the estimation accuracy. Computer simulations are implemented to verify the effectiveness of the proposed algorithm. PMID:25668212

  18. Localization and mass spectra of various matter fields on scalar-tensor brane

    SciTech Connect

    Xie, Qun-Ying; Zhao, Zhen-Hua; Zhong, Yi; Yang, Jie; Zhou, Xiang-Nan

    2015-03-10

    Recently, a new scalar-tensor braneworld model was presented in [http://dx.doi.org/10.1103/PhysRevD.86.127502]. It not only solves the gauge hierarchy problem but also reproduces a correct Friedmann-like equation on the brane. In this new model, there are two different brane solutions, for which the mass spectra of gravity on the brane are the same. In this paper, we investigate localization and mass spectra of various bulk matter fields (i.e., scalar, vector, Kalb-Ramond, and fermion fields) on the brane. It is shown that the zero modes of all the matter fields can be localized on the positive tension brane under some conditions, and the mass spectra of each kind of bulk matter field for the two brane solutions are different except for some special cases, which implies that the two brane solutions are not physically equivalent. When the coupling constants between the dilaton and bulk matter fields take special values, the mass spectra for both solutions are the same, and the scalar and vector zero modes are localized on the negative tension brane, while the KR zero mode is still localized on the positive tension brane.

  19. Local modulation of steroid action: rapid control of enzymatic activity

    PubMed Central

    Charlier, Thierry D.; Cornil, Charlotte A.; Patte-Mensah, Christine; Meyer, Laurence; Mensah-Nyagan, A. Guy; Balthazart, Jacques

    2015-01-01

    Estrogens can induce rapid, short-lived physiological and behavioral responses, in addition to their slow, but long-term, effects at the transcriptional level. To be functionally relevant, these effects should be associated with rapid modulations of estrogens concentrations. 17β-estradiol is synthesized by the enzyme aromatase, using testosterone as a substrate, but can also be degraded into catechol-estrogens via hydroxylation by the same enzyme, leading to an increase or decrease in estrogens concentration, respectively. The first evidence that aromatase activity (AA) can be rapidly modulated came from experiments performed in Japanese quail hypothalamus homogenates. This rapid modulation is triggered by calcium-dependent phosphorylations and was confirmed in other tissues and species. The mechanisms controlling the phosphorylation status, the targeted amino acid residues and the reversibility seem to vary depending of the tissues and is discussed in this review. We currently do not know whether the phosphorylation of the same amino acid affects both aromatase and/or hydroxylase activities or whether these residues are different. These processes provide a new general mechanism by which local estrogen concentration can be rapidly altered in the brain and other tissues. PMID:25852459

  20. Control of tissue growth by locally produced activator: Liver regeneration

    NASA Astrophysics Data System (ADS)

    Zhdanov, Vladimir P.

    2015-03-01

    In general, the tissue development is controlled by growth factors and depends on the biomechanics of cells. The corresponding kinetic models are focused primarily on the early stages of the development. The attempts to construct such models for the later stages are still rare. One of the notable examples here is liver regeneration. Referring to this process, the author proposes and analyzes a generic kinetic model describing the regulation of tissue growth by locally produced activator. The model includes activator diffusion and control of the rate of cell proliferation which is described by using the Hill expression. Although this control may be moderately or strongly non-linear, the qualitative changes in the regeneration kinetics are predicted to be modest. For moderately non-linear control, the evolution of the tissue volume to the steady-state value exhibits an initial relatively short linear stage and then becomes slightly slower so that the whole kinetics is close to exponential. For strongly non-linear control, the linear stage dominates and/or the kinetics may exhibit a S-like shape feature which is, however, rather weak. The identification of such qualitative features in experimentally measured kinetics is shown to be difficult, because the error bars in the experiments are typically too large.

  1. Temporal variability of local abundance, sex ratio and activity in the Sardinian chalk hill blue butterfly

    USGS Publications Warehouse

    Casula, P.; Nichols, J.D.

    2003-01-01

    When capturing and marking of individuals is possible, the application of newly developed capture-recapture models can remove several sources of bias in the estimation of population parameters such as local abundance and sex ratio. For example, observation of distorted sex ratios in counts or captures can reflect either different abundances of the sexes or different sex-specific capture probabilities, and capture-recapture models can help distinguish between these two possibilities. Robust design models and a model selection procedure based on information-theoretic methods were applied to study the local population structure of the endemic Sardinian chalk hill blue butterfly, Polyommatus coridon gennargenti. Seasonal variations of abundance, plus daily and weather-related variations of active populations of males and females were investigated. Evidence was found of protandry and male pioneering of the breeding space. Temporary emigration probability, which describes the proportion of the population not exposed to capture (e.g. absent from the study area) during the sampling process, was estimated, differed between sexes, and was related to temperature, a factor known to influence animal activity. The correlation between temporary emigration and average daily temperature suggested interpreting temporary emigration as inactivity of animals. Robust design models were used successfully to provide a detailed description of the population structure and activity in this butterfly and are recommended for studies of local abundance and animal activity in the field.

  2. Local adaptive approach toward segmentation of microscopic images of activated sludge flocs

    NASA Astrophysics Data System (ADS)

    Khan, Muhammad Burhan; Nisar, Humaira; Ng, Choon Aun; Lo, Po Kim; Yap, Vooi Voon

    2015-11-01

    Activated sludge process is a widely used method to treat domestic and industrial effluents. The conditions of activated sludge wastewater treatment plant (AS-WWTP) are related to the morphological properties of flocs (microbial aggregates) and filaments, and are required to be monitored for normal operation of the plant. Image processing and analysis is a potential time-efficient monitoring tool for AS-WWTPs. Local adaptive segmentation algorithms are proposed for bright-field microscopic images of activated sludge flocs. Two basic modules are suggested for Otsu thresholding-based local adaptive algorithms with irregular illumination compensation. The performance of the algorithms has been compared with state-of-the-art local adaptive algorithms of Sauvola, Bradley, Feng, and c-mean. The comparisons are done using a number of region- and nonregion-based metrics at different microscopic magnifications and quantification of flocs. The performance metrics show that the proposed algorithms performed better and, in some cases, were comparable to the state-of the-art algorithms. The performance metrics were also assessed subjectively for their suitability for segmentations of activated sludge images. The region-based metrics such as false negative ratio, sensitivity, and negative predictive value gave inconsistent results as compared to other segmentation assessment metrics.

  3. Local motion detectors are required for the computation of expansion flow-fields

    PubMed Central

    Schilling, Tabea; Borst, Alexander

    2015-01-01

    ABSTRACT Avoidance of predators or impending collisions is important for survival. Approaching objects can be mimicked by expanding flow-fields. Tethered flying fruit flies, when confronted with an expansion flow-field, reliably turn away from the pole of expansion when presented laterally, or perform a landing response when presented frontally. Here, we show that the response to an expansion flow-field is independent of the overall luminance change and edge acceleration. As we demonstrate by blocking local motion-sensing neurons T4 and T5, the response depends crucially on the neural computation of appropriately aligned local motion vectors, using the same hardware that also controls the optomotor response to rotational flow-fields. PMID:26231626

  4. Conjugate field approaches for active array compensation

    NASA Technical Reports Server (NTRS)

    Acosta, R. J.

    1989-01-01

    Two approaches for calculating the compensating feed array complex excitations are namely, the indirect conjugate field matching (ICFM) and the direct conjugate field matching (DCFM) approach. In the ICFM approach the compensating feed array excitations are determined by considering the transmitting mode and the reciprocity principle. The DCF, in contrast calculates the array excitations by integrating directly the induced surface currents on the reflector under a receiving mode. DCFM allows the reflector to be illuminated by an incident plane wave with a tapered amplitude. The level of taper can effectively control the sidelobe level of the compensated antenna pattern. Both approaches are examined briefly.

  5. Effect of diagonal disorder on the upper critical field of the local electron pair system

    NASA Astrophysics Data System (ADS)

    Li, Yan-Min; Zhang, Li-Yuan

    1989-06-01

    The effect of diagonal disorder on the upper critical magnetic field (Hc2) of the local electron pair system is studied in the framework of the mean-field approximation. It is found that the disorder strongly perturbs the temperature dependences of Hc2. The theoretical calculations are also compared with experimental Hc2 data on the heavy fermion superconductors CeCu2Si2 and UPt3. Similar temperature dependences are found.

  6. Local time asymmetries and toroidal field line resonances: Global magnetospheric modeling in SWMF

    NASA Astrophysics Data System (ADS)

    Ellington, S. M.; Moldwin, M. B.; Liemohn, M. W.

    2016-03-01

    We present evidence of resonant wave-wave coupling via toroidal field line resonance (FLR) signatures in the Space Weather Modeling Framework's (SWMF) global, terrestrial magnetospheric model in one simulation driven by a synthetic upstream solar wind with embedded broadband dynamic pressure fluctuations. Using in situ, stationary point measurements of the radial electric field along the 1500 LT meridian, we show that SWMF reproduces a multiharmonic, continuous distribution of FLRs exemplified by 180° phase reversals and amplitude peaks across the resonant L shells. By linearly increasing the amplitude of the dynamic pressure fluctuations in time, we observe a commensurate increase in the amplitude of the radial electric and azimuthal magnetic field fluctuations, which is consistent with the solar wind driver being the dominant source of the fast mode energy. While we find no discernible local time changes in the FLR frequencies despite large-scale, monotonic variations in the dayside equatorial mass density, in selectively sampling resonant points and examining spectral resonance widths, we observe significant radial, harmonic, and time-dependent local time asymmetries in the radial electric field amplitudes. A weak but persistent local time asymmetry exists in measures of the estimated coupling efficiency between the fast mode and toroidal wave fields, which exhibits a radial dependence consistent with the coupling strength examined by Mann et al. (1999) and Zhu and Kivelson (1988). We discuss internal structural mechanisms and additional external energy sources that may account for these asymmetries as we find that local time variations in the strength of the compressional driver are not the predominant source of the FLR amplitude asymmetries. These include resonant mode coupling of observed Kelvin-Helmholtz surface wave generated Pc5 band ultralow frequency pulsations, local time differences in local ionospheric dampening rates, and variations in azimuthal

  7. Spectral distribution of local field potential responses to electrical stimulation of the retina

    NASA Astrophysics Data System (ADS)

    Wong, Yan T.; Halupka, Kerry; Kameneva, Tatiana; Cloherty, Shaun L.; Grayden, David B.; Burkitt, Anthony N.; Meffin, Hamish; Shivdasani, Mohit N.

    2016-06-01

    Objective. Different frequency bands of the local field potential (LFP) have been shown to reflect neuronal activity occurring at varying cortical scales. As such, recordings of the LFP may offer a novel way to test the efficacy of neural prostheses and allow improvement of stimulation strategies via neural feedback. Here we use LFP measurements from visual cortex to characterize neural responses to electrical stimulation of the retina. We aim to show that the LFP is a viable signal that contains sufficient information to optimize the performance of sensory neural prostheses. Approach. Clinically relevant electrode arrays were implanted in the suprachoroidal space of one eye in four felines. LFPs were simultaneously recorded in response to stimulation of individual electrodes using penetrating microelectrode arrays from the visual cortex. The frequency response of each electrode was extracted using multi-taper spectral analysis and the uniqueness of the responses was determined via a linear decoder. Main results. We found that cortical LFPs are reliably modulated by electrical stimulation of the retina and that the responses are spatially localized. We further characterized the spectral distribution of responses, with maximum information being contained in the low and high gamma bands. Finally, we found that LFP responses are unique to a large range of stimulus parameters (∼40) with a maximum conveyable information rate of 6.1 bits. Significance. These results show that the LFP can be used to validate responses to electrical stimulation of the retina and we provide the first steps towards using these responses to provide more efficacious stimulation strategies.

  8. Phase shifts in precision atom interferometry due to the localization of atoms and optical fields

    SciTech Connect

    Wicht, A.; Sarajlic, E.; Hensley, J.M.; Chu, S.

    2005-08-15

    We discuss details of momentum transfer in the interaction between localized atoms and localized optical fields which are relevant to precision atom interferometry. Specifically, we consider a {lambda}-type atom coherently driven between its ground states by a bichromatic optical field. We assume that the excited state can be eliminated adiabatically from the time evolution. It is shown that the average recoil momentum is given by the phase gradient of the two-photon field at the 'position' of the atom, provided that the optical field can be described by a function which is separable in position and time and that the atomic wave function is symmetric and well localized within the optical field envelope. The result does not require the optical fields to have a Gaussian spatial dependence. Our discussion provides the basis for the analysis of systematic errors in precision atom interferometry arising from optical wave-front curvature, wave-front distortion, and the Gouy phase shift of Gaussian beams. We apply our result to the atom interferometer experiment of Chu and co-workers which measures the fine-structure constant.

  9. Forecasting the Solar photospheric magnetic field using solar flux transport model and local ensemble Kalman filtering

    NASA Astrophysics Data System (ADS)

    Zhang, Y.

    2015-12-01

    Accurate forecasting the solar photospheric magnetic field distribution play an important role in the estimates of the inner boundary conditions of the coronal and solar wind model. Forecasting solar photospheric magnetic field using the solar flux transport (SFT) model can achieve an acceptable match to the actual field. The observations from ground-based or spacecraft instruments can be assimilated to update the modeled flux. The local ensemble Kalman filtering (LEnKF) method is utilized to improve forecasts and characterize their uncertainty by propagating the SFT model with different model parameters forward in time to control the evolution of the solar photospheric magnetic field. Optimal assimilation of measured data into the ensemble produces an improvement in the fit of the forecast to the actual field. Our approach offers a method to improve operational forecasting of the solar photospheric magnetic field. The LEnKF method also allows sensitivity analysis of the SFT model to noise and uncertainty within the physical representation.

  10. Forecasting the solar photospheric magnetic field using solar flux transport model and local ensemble Kalman filtering

    NASA Astrophysics Data System (ADS)

    Zhang, Ying; Du, Aimin; Feng, Xueshang

    2015-04-01

    Accurate forecasting the solar photospheric magnetic field distribution play an important role in the estimates of the inner boundary conditions of the coronal and solar wind model. Forecasting solar photospheric magnetic field using the solar flux transport (SFT) model can achieve an acceptable match to the actual field. The observations from ground-based or spacecraft instruments can be assimilated to update the modeled flux. The local ensemble Kalman filtering (LEnKF) method is utilized to improve forecasts and characterize their uncertainty by propagating the SFT model with different model parameters forward in time to control the evolution of the solar photospheric magnetic field. Optimal assimilation of measured data into the ensemble produces an improvement in the fit of the forecast to the actual field. Our approach offers a method to improve operational forecasting of the solar photospheric magnetic field. The LEnKF method also allows sensitivity analysis of the SFT model to noise and uncertainty within the physical representation.

  11. A new method for matched field localization based on two-hydrophone

    NASA Astrophysics Data System (ADS)

    Li, Kun; Fang, Shi-liang

    2015-03-01

    The conventional matched field processing (MFP) uses large vertical arrays to locate an underwater acoustic target. However, the use of large vertical arrays increases equipment and computational cost, and causes some problems such as element failures, and array tilting to degrade the localization performance. In this paper, the matched field localization method using two-hydrophone is proposed for underwater acoustic pulse signals with an unknown emitted signal waveform. Using the received signal of hydrophones and the ocean channel pulse response which can be calculated from an acoustic propagation model, the spectral matrix of the emitted signal for different source locations can be estimated by employing the method of frequency domain least squares. The resulting spectral matrix of the emitted signal for every grid region is then multiplied by the ocean channel frequency response matrix to generate the spectral matrix of replica signal. Finally, the matched field localization using two-hydrophone for underwater acoustic pulse signals of an unknown emitted signal waveform can be estimated by comparing the difference between the spectral matrixes of the received signal and the replica signal. The simulated results from a shallow water environment for broadband signals demonstrate the significant localization performance of the proposed method. In addition, the localization accuracy in five different cases are analyzed by the simulation trial, and the results show that the proposed method has a sharp peak and low sidelobes, overcoming the problem of high sidelobes in the conventional MFP due to lack of the number of elements.

  12. Comparison of Phase-Based 3D Near-Field Source Localization Techniques for UHF RFID.

    PubMed

    Parr, Andreas; Miesen, Robert; Vossiek, Martin

    2016-01-01

    In this paper, we present multiple techniques for phase-based narrowband backscatter tag localization in three-dimensional space with planar antenna arrays or synthetic apertures. Beamformer and MUSIC localization algorithms, known from near-field source localization and direction-of-arrival estimation, are applied to the 3D backscatter scenario and their performance in terms of localization accuracy is evaluated. We discuss the impact of different transceiver modes known from the literature, which evaluate different send and receive antenna path combinations for a single localization, as in multiple input multiple output (MIMO) systems. Furthermore, we propose a new Singledimensional-MIMO (S-MIMO) transceiver mode, which is especially suited for use with mobile robot systems. Monte-Carlo simulations based on a realistic multipath error model ensure spatial correlation of the simulated signals, and serve to critically appraise the accuracies of the different localization approaches. A synthetic uniform rectangular array created by a robotic arm is used to evaluate selected localization techniques. We use an Ultra High Frequency (UHF) Radiofrequency Identification (RFID) setup to compare measurements with the theory and simulation. The results show how a mean localization accuracy of less than 30 cm can be reached in an indoor environment. Further simulations demonstrate how the distance between aperture and tag affects the localization accuracy and how the size and grid spacing of the rectangular array need to be adapted to improve the localization accuracy down to orders of magnitude in the centimeter range, and to maximize array efficiency in terms of localization accuracy per number of elements. PMID:27347976

  13. Comparison of Phase-Based 3D Near-Field Source Localization Techniques for UHF RFID

    PubMed Central

    Parr, Andreas; Miesen, Robert; Vossiek, Martin

    2016-01-01

    In this paper, we present multiple techniques for phase-based narrowband backscatter tag localization in three-dimensional space with planar antenna arrays or synthetic apertures. Beamformer and MUSIC localization algorithms, known from near-field source localization and direction-of-arrival estimation, are applied to the 3D backscatter scenario and their performance in terms of localization accuracy is evaluated. We discuss the impact of different transceiver modes known from the literature, which evaluate different send and receive antenna path combinations for a single localization, as in multiple input multiple output (MIMO) systems. Furthermore, we propose a new Singledimensional-MIMO (S-MIMO) transceiver mode, which is especially suited for use with mobile robot systems. Monte-Carlo simulations based on a realistic multipath error model ensure spatial correlation of the simulated signals, and serve to critically appraise the accuracies of the different localization approaches. A synthetic uniform rectangular array created by a robotic arm is used to evaluate selected localization techniques. We use an Ultra High Frequency (UHF) Radiofrequency Identification (RFID) setup to compare measurements with the theory and simulation. The results show how a mean localization accuracy of less than 30 cm can be reached in an indoor environment. Further simulations demonstrate how the distance between aperture and tag affects the localization accuracy and how the size and grid spacing of the rectangular array need to be adapted to improve the localization accuracy down to orders of magnitude in the centimeter range, and to maximize array efficiency in terms of localization accuracy per number of elements. PMID:27347976

  14. Electric-field-induced local and mesoscale structural changes in polycrystalline dielectrics and ferroelectrics

    DOE PAGESBeta

    Usher, Tedi -Marie; Levin, Igor; Daniels, John E.; Jones, Jacob L.

    2015-10-01

    In this study, the atomic-scale response of dielectrics/ferroelectrics to electric fields is central to their functionality. Here we introduce an in situ characterization method that reveals changes in the local atomic structure in polycrystalline materials under fields. The method employs atomic pair distribution functions (PDFs), determined from X-ray total scattering that depends on orientation relative to the applied field, to probe structural changes over length scales from sub-Ångstrom to several nanometres. The PDF is sensitive to local ionic displacements and their short-range order, a key uniqueness relative to other techniques. The method is applied to representative ferroelectrics, BaTiO3 and Na½Bi½TiO3,more » and dielectric SrTiO3. For Na½Bi½TiO3, the results reveal an abrupt field-induced monoclinic to rhombohedral phase transition, accompanied by ordering of the local Bi displacements and reorientation of the nanoscale ferroelectric domains. For BaTiO3 and SrTiO3, the local/nanoscale structural changes observed in the PDFs are dominated by piezoelectric lattice strain and ionic polarizability, respectively.« less

  15. Electric-field-induced local and mesoscale structural changes in polycrystalline dielectrics and ferroelectrics

    SciTech Connect

    Usher, Tedi -Marie; Levin, Igor; Daniels, John E.; Jones, Jacob L.

    2015-10-01

    In this study, the atomic-scale response of dielectrics/ferroelectrics to electric fields is central to their functionality. Here we introduce an in situ characterization method that reveals changes in the local atomic structure in polycrystalline materials under fields. The method employs atomic pair distribution functions (PDFs), determined from X-ray total scattering that depends on orientation relative to the applied field, to probe structural changes over length scales from sub-Ångstrom to several nanometres. The PDF is sensitive to local ionic displacements and their short-range order, a key uniqueness relative to other techniques. The method is applied to representative ferroelectrics, BaTiO3 and Na½Bi½TiO3, and dielectric SrTiO3. For Na½Bi½TiO3, the results reveal an abrupt field-induced monoclinic to rhombohedral phase transition, accompanied by ordering of the local Bi displacements and reorientation of the nanoscale ferroelectric domains. For BaTiO3 and SrTiO3, the local/nanoscale structural changes observed in the PDFs are dominated by piezoelectric lattice strain and ionic polarizability, respectively.

  16. Electric-field-induced local and mesoscale structural changes in polycrystalline dielectrics and ferroelectrics

    PubMed Central

    Usher, Tedi-Marie; Levin, Igor; Daniels, John E.; Jones, Jacob L.

    2015-01-01

    The atomic-scale response of dielectrics/ferroelectrics to electric fields is central to their functionality. Here we introduce an in situ characterization method that reveals changes in the local atomic structure in polycrystalline materials under fields. The method employs atomic pair distribution functions (PDFs), determined from X-ray total scattering that depends on orientation relative to the applied field, to probe structural changes over length scales from sub-Ångstrom to several nanometres. The PDF is sensitive to local ionic displacements and their short-range order, a key uniqueness relative to other techniques. The method is applied to representative ferroelectrics, BaTiO3 and Na½Bi½TiO3, and dielectric SrTiO3. For Na½Bi½TiO3, the results reveal an abrupt field-induced monoclinic to rhombohedral phase transition, accompanied by ordering of the local Bi displacements and reorientation of the nanoscale ferroelectric domains. For BaTiO3 and SrTiO3, the local/nanoscale structural changes observed in the PDFs are dominated by piezoelectric lattice strain and ionic polarizability, respectively. PMID:26424360

  17. Quantum Gravity from the Point of View of Locally Covariant Quantum Field Theory

    NASA Astrophysics Data System (ADS)

    Brunetti, Romeo; Fredenhagen, Klaus; Rejzner, Katarzyna

    2016-08-01

    We construct perturbative quantum gravity in a generally covariant way. In particular our construction is background independent. It is based on the locally covariant approach to quantum field theory and the renormalized Batalin-Vilkovisky formalism. We do not touch the problem of nonrenormalizability and interpret the theory as an effective theory at large length scales.

  18. Use of Microscale Landforms to Teach Introductory Physical Geography: Planning a Local Field Exercise.

    ERIC Educational Resources Information Center

    Luft, Edward R.

    1990-01-01

    States that firsthand observations of the dynamic process that shapes landforms are important to understanding physical geography. Posits that locally planned, short-duration field exercises to study miniature or fourth-order landforms will enhance instruction about these fundamental geographic concepts. (DB)

  19. Theory of long period magnetic pulsations, 3. Local field line oscillations

    SciTech Connect

    Hasegawa, A.; Tsui, K.H.; Assis, A.S.

    1983-08-01

    The local magnetic field is shown to oscillate at its Alfven resonance frequency (ies) in response to a wide band source whose frequency range covers the resonance frequency (ies). The proposed mechanism explains certain observations of magnetic pulsations where the frequency is found to vary continuously as a function of latitude for a given event.

  20. Local field and quantum effects for current perpendicular to planes in multilayers

    SciTech Connect

    Zhang, X.G.; Butler, W.H.

    1996-12-31

    The calculation of giant-magnetoresistance and in general, of electron transport for multilayers in the case of current perpendicular to the planes (CPP) requires both the two-point conductivity and the solution to the local field problem. In this paper we present a solution to the local field problem at an interface using two approaches. In the first approach we find the semiclassical solution for the local field when there is a band mismatch between two sides of an interface, and examine the deviation of the total resistance from the result of ``self-averaging``, in the lowest order of the value of the potential step. In the second approach, we solve for the quantum correction to the local field through a numerical iterative scheme. The oscillations due to the quantum correction are surprisingly large, but their correction to the total resistance is remarkably small. Our results imply that the ``self-averaging`` of the resistance, which is usually assumed in analysis of CPP, is only approximate. 8 refs., 2 figs., 2 tabs.

  1. Evoked Potentials in Motor Cortical Local Field Potentials Reflect Task Timing and Behavioral Performance

    PubMed Central

    Confais, Joachim; Ponce-Alvarez, Adrián; Diesmann, Markus; Riehle, Alexa

    2010-01-01

    Evoked potentials (EPs) are observed in motor cortical local field potentials (LFPs) during movement execution (movement-related potentials [MRPs]) and in response to relevant visual cues (visual evoked potentials [VEPs]). Motor cortical EPs may be directionally selective, but little is known concerning their relation to other aspects of motor behavior, such as task timing and performance. We recorded LFPs in motor cortex of two monkeys during performance of a precued arm-reaching task. A time cue at the start of each trial signaled delay duration and thereby the pace of the task and the available time for movement preparation. VEPs and MRPs were strongly modulated by the delay duration, VEPs being systematically larger in short-delay trials and MRPs larger in long-delay trials. Despite these systematic modulations related to the task timing, directional selectivity was similar in short and long trials. The behavioral reaction time was positively correlated with MRP size and negatively correlated with VEP size, within sessions. In addition, the behavioral performance improved across sessions, in parallel with a slow decrease in the size of VEPs and MRPs. Our results clearly show the strong influence of the behavioral context and performance on motor cortical population activity during movement preparation and execution. PMID:20884766

  2. Effect of amplitude correlations on coherence in the local field potential.

    PubMed

    Srinath, Ramanujan; Ray, Supratim

    2014-08-15

    Neural activity across the brain shows both spatial and temporal correlations at multiple scales, and understanding these correlations is a key step toward understanding cortical processing. Correlation in the local field potential (LFP) recorded from two brain areas is often characterized by computing the coherence, which is generally taken to reflect the degree of phase consistency across trials between two sites. Coherence, however, depends on two factors-phase consistency as well as amplitude covariation across trials-but the spatial structure of amplitude correlations across sites and its contribution to coherence are not well characterized. We recorded LFP from an array of microelectrodes chronically implanted in the primary visual cortex of monkeys and studied correlations in amplitude across electrodes as a function of interelectrode distance. We found that amplitude correlations showed a similar trend as coherence as a function of frequency and interelectrode distance. Importantly, even when phases were completely randomized between two electrodes, amplitude correlations introduced significant coherence. To quantify the contributions of phase consistency and amplitude correlations to coherence, we simulated pairs of sinusoids with varying phase consistency and amplitude correlations. These simulations confirmed that amplitude correlations can significantly bias coherence measurements, resulting in either over- or underestimation of true phase coherence. Our results highlight the importance of accounting for the correlations in amplitude while using coherence to study phase relationships across sites and frequencies. PMID:24790174

  3. Detecting non-linearities in neuro-electrical signals: A study of synchronous local field potentials

    NASA Astrophysics Data System (ADS)

    Müller-Gerking, Johannes; Martinerie, Jacques; Neuenschwander, Sergio; Pezard, Laurent; Renault, Bernard; Varela, Francisco J.

    The question of the presence and detection of non-linear dynamics and possibly low-dimensional chaos in the brain is still an open question, with recent results indicating that initial claims for low dimensionality were faulted by incomplete statistical testing. To make some progress on this question, our approach was to use stringent data analysis of precisely controlled and behaviorally significant neuroelectric data. There are strong indications that functional brain activity is correlated with synchronous local field potentials. We examine here such synchronous episodes in data recorded from the visual system of behaving cats and pigeons. Our purpose was to examine under these ideal conditions whether the time series showed any evidence of non-linearity concommitantly with the arising of synchrony. To test for non-linearity we have used surrogate sets for non-linear forecasting, the false nearest strands method, and an examination of deterministic vs stochastic modeling. Our results indicate that the time series under examination do show evidence for traces of non-linear dynamics but weakly, since they are not robust under changes of parameters. We conclude that low-dimensional chaos is unlikely to be found in the brain, and that a robust detection and characterization of higher-dimensional non-linear dynamics is beyond the reach of current analytical tools.

  4. Tuning Localized Surface Plasmon Resonance in Scanning Near-Field Optical Microscopy Probes.

    PubMed

    Vasconcelos, Thiago L; Archanjo, Bráulio S; Fragneaud, Benjamin; Oliveira, Bruno S; Riikonen, Juha; Li, Changfeng; Ribeiro, Douglas S; Rabelo, Cassiano; Rodrigues, Wagner N; Jorio, Ado; Achete, Carlos A; Cançado, Luiz Gustavo

    2015-06-23

    A reproducible route for tuning localized surface plasmon resonance in scattering type near-field optical microscopy probes is presented. The method is based on the production of a focused-ion-beam milled single groove near the apex of electrochemically etched gold tips. Electron energy-loss spectroscopy and scanning transmission electron microscopy are employed to obtain highly spatially and spectroscopically resolved maps of the milled probes, revealing localized surface plasmon resonance at visible and near-infrared wavelengths. By changing the distance L between the groove and the probe apex, the localized surface plasmon resonance energy can be fine-tuned at a desired absorption channel. Tip-enhanced Raman spectroscopy is applied as a test platform, and the results prove the reliability of the method to produce efficient scattering type near-field optical microscopy probes. PMID:26027751

  5. Behavior of Caenorhabditis elegans in alternating electric field and its application to their localization and control

    NASA Astrophysics Data System (ADS)

    Rezai, Pouya; Siddiqui, Asad; Selvaganapathy, Ponnambalam Ravi; Gupta, Bhagwati P.

    2010-04-01

    Caenorhabditis elegans is an attractive model organism because of its genetic similarity to humans and the ease of its manipulation in the laboratory. Recently, it was shown that a direct current electric field inside microfluidic channel induces directed movement that is highly sensitive, reliable, and benign. In this letter, we describe the worm's movement response to alternating electric fields in a similar channel setup. We demonstrate that the 1 Hz and higher frequency of alternating current field can effectively localize worms in the channel. This discovery could potentially help design microfluidic devices for high throughput automated analysis of worms.

  6. Particle localization in a double-well potential by pseudo-supersymmetric fields

    SciTech Connect

    Bagrov, V. G. Samsonov, B. F.; Shamshutdinova, V. V.

    2011-06-15

    We study properties of a particle moving in a double-well potential in the two-level approximation placed in an additional external time-dependent field. Using previously established property (J. Phys. A 41, 244023 (2008)) that any two-level system possesses a pseudo-supersymmetry we introduce the notion of pseudo-supersymmetric field. It is shown that these fields, even if their time dependence is not periodical, may produce the effect of localization of the particle in one of the wells of the double-well potential.

  7. Tuning nano electric field to affect restrictive membrane area on localized single cell nano-electroporation

    NASA Astrophysics Data System (ADS)

    Santra, Tuhin Subhra; Wang, Pen-Cheng; Chang, Hwan-You; Tseng, Fan-Gang

    2013-12-01

    Interaction of electric field with biological cells is an important phenomenon for field induced drug delivery system. We demonstrate a selective and localized single cell nano-electroporation (LSCNEP) by applying an intense electric field on a submicron region of the single cell membrane, which can effectively allow high efficient molecular delivery but low cell damage. The delivery rate is controlled by adjusting transmembrane potential and manipulating membrane status. Thermal and ionic influences are deteriorated from the cell membrane by dielectric passivation. Either reversible or irreversible by LSCNEP can fully controlled with potential applications in medical diagnostics and biological studies.

  8. Enhancement of visual responsiveness by spontaneous local network activity in vivo.

    PubMed

    Haider, Bilal; Duque, Alvaro; Hasenstaub, Andrea R; Yu, Yuguo; McCormick, David A

    2007-06-01

    Spontaneous activity within local circuits affects the integrative properties of neurons and networks. We have previously shown that neocortical network activity exhibits a balance between excitatory and inhibitory synaptic potentials, and such activity has significant effects on synaptic transmission, action potential generation, and spike timing. However, whether such activity facilitates or reduces sensory responses has yet to be clearly determined. We examined this hypothesis in the primary visual cortex in vivo during slow oscillations in ketamine-xylazine anesthetized cats. We measured network activity (Up states) with extracellular recording, while simultaneously recording postsynaptic potentials (PSPs) and action potentials in nearby cells. Stimulating the receptive field revealed that spiking responses of both simple and complex cells were significantly enhanced (>2-fold) during network activity, as were spiking responses to intracellular injection of varying amplitude artificial conductance stimuli. Visually evoked PSPs were not significantly different in amplitude during network activity or quiescence; instead, spontaneous depolarization caused by network activity brought these evoked PSPs closer to firing threshold. Further examination revealed that visual responsiveness was gradually enhanced by progressive membrane potential depolarization. These spontaneous depolarizations enhanced responsiveness to stimuli of varying contrasts, resulting in an upward (multiplicative) scaling of the contrast response function. Our results suggest that small increases in ongoing balanced network activity that result in depolarization may provide a rapid and generalized mechanism to control the responsiveness (gain) of cortical neurons, such as occurs during shifts in spatial attention. PMID:17409168

  9. Stress Field in Brazil with Focal Mechanism: Regional and Local Patterns

    NASA Astrophysics Data System (ADS)

    Dias, F.; Assumpcao, M.

    2013-05-01

    determine focal mechanism of low magnitudes events (< 5.0 mb) using distant s seismograph stations. We find examples of stress perturbations induced by local effects (e.g. flexure and continental spreading). The results of this work should be useful for future numerical modeling of intraplate stress field. Assumpção,M.,1998.Seismicity and stresses in the Brazilian passive margin. Bull. Seism. Soc. Am., 88(1),160-169. Herrmann, R. B. (2002). Computer programs in seismology, St. Louis University Earthquake Center, St. Louis, Missouri, www.eas.slu .edu/eqc/eqccps.html. Lithgow-Bertelloni, C., & J.H. Guynn, 2004. Origin of the lithospheric stress field. J. Geophys. Res., 109, B01408, doi:10.1029/2003JB002467. Meijer, P.T., 1995. Dynamics of active continental margins: the Andes and the Aegean regions. PhD Thesis, Utrecht University, The Netherlands. Sokos, E., Zahradnik, J., (2008). ISOLA a Fortran code and a Matlab GUI to perform multiple-point source inversion of seismic data, Computers and Geosciences, 34, 967-97. Watts, A. B., M. Rodger, C. Peirce, C. J. Greenroyd, and R. W. Hobbs (2009). Seismic structure, gravity anomalies, and flexure of the Amazon continental margin, NE Brazil, J. Geophys. Res., 114, B07103, doi:10.1029/2008JB006259.

  10. Intraplate Stress Field in Brazil Using Focal Mechanisms: Regional and Local Patterns: Examples of Regional Forces Controlling the Stress Field

    NASA Astrophysics Data System (ADS)

    Dias, F. L.; Assumpcao, M.

    2014-12-01

    The knowledge of stress field is fundamental not only to understand driving forces and plate deformation but also in the study of intraplate seismicity. In Brazil, the stress field has been determined mainly using focal mechanisms and a breakout data and in-situ measurements. However, the stress field still is poorly known in Brazil. We show a recent compilation of focal mechanism determined in Brazil (Fig 1). The focal mechanisms of some recent earthquakes (magnitude lower than 5 mb) were studied using waveform modeling. We stacked the record of several teleseismic stations (> 30°) with a good signal/noise ratio and we grouped then according to distance and azimuth. With the focal mechanisms available in literature and those obtained in this work, we were able to identify some patterns: the central region shows compressional pattern (E-W SHmax), which is predicted by regional theoretical models ( Coblentz & Richardson, 1996 and the TD0 model of Lithgow & Bertelloni, 2004). This compression is mainly due to the interaction of tectonic plate forces. Meanwhile in the Amazon region, we find an indication of SHMax oriented in the SE-NW direction, probably caused by the Caribbean plate interaction (Meijer, 1995) and Amazon Fan, we have flexural stresses caused by sedimentary load with is in agreement with local theoretical models (Watts et al., 2009) . In northern coastal region, the compression rotates following the coastline, which indicates an important local component related to spreading effects at the continental/oceanic transition (Assumpção, 1998). We determine the focal mechanism of several events in Brazil using different techniques according to the available data. The major difficulty is to determine focal mechanism of low magnitudes events (< 5.0 mb) using distant or few seismograph stations. We find examples of stress perturbations induced by local effects (e.g. flexure and continental spreading). The results of this work should be useful for future

  11. Goldstone field test activities: Target search

    NASA Technical Reports Server (NTRS)

    Tarter, J.

    1986-01-01

    In March of this year prototype SETI equipment was installed at DSS13, the 26 meter research and development antenna at NASA's Goldstone complex of satellite tracking dishes. The SETI equipment will remain at this site at least through the end of the summer so that the hardware and software developed for signal detection and recognition can be fully tested in a dynamic observatory environment. The field tests are expected to help understand which strategies for observing and which signal recognition algorithms perform best in the presence of strong man-made interfering signals (RFI) and natural astronomical sources.

  12. The active titration method for measuring local hydroxyl radical concentration

    NASA Technical Reports Server (NTRS)

    Sprengnether, Michele; Prinn, Ronald G.

    1994-01-01

    We are developing a method for measuring ambient OH by monitoring its rate of reaction with a chemical species. Our technique involves the local, instantaneous release of a mixture of saturated cyclic hydrocarbons (titrants) and perfluorocarbons (dispersants). These species must not normally be present in ambient air above the part per trillion concentration. We then track the mixture downwind using a real-time portable ECD tracer instrument. We collect air samples in canisters every few minutes for roughly one hour. We then return to the laboratory and analyze our air samples to determine the ratios of the titrant to dispersant concentrations. The trends in these ratios give us the ambient OH concentration from the relation: dlnR/dt = -k(OH). A successful measurement of OH requires that the trends in these ratios be measureable. We must not perturb ambient OH concentrations. The titrant to dispersant ratio must be spatially invariant. Finally, heterogeneous reactions of our titrant and dispersant species must be negligible relative to the titrant reaction with OH. We have conducted laboratory studies of our ability to measure the titrant to dispersant ratios as a function of concentration down to the few part per trillion concentration. We have subsequently used these results in a gaussian puff model to estimate our expected uncertainty in a field measurement of OH. Our results indicate that under a range of atmospheric conditions we expect to be able to measure OH with a sensitivity of 3x10(exp 5) cm(exp -3). In our most optimistic scenarios, we obtain a sensitivity of 1x10(exp 5) cm(exp -3). These sensitivity values reflect our anticipated ability to measure the ratio trends. However, because we are also using a rate constant to obtain our (OH) from this ratio trend, our accuracy cannot be better than that of the rate constant, which we expect to be about 20 percent.

  13. Non-linear non-local molecular electrodynamics with nano-optical fields.

    PubMed

    Chernyak, Vladimir Y; Saurabh, Prasoon; Mukamel, Shaul

    2015-10-28

    The interaction of optical fields sculpted on the nano-scale with matter may not be described by the dipole approximation since the fields may vary appreciably across the molecular length scale. Rather than incrementally adding higher multipoles, it is advantageous and more physically transparent to describe the optical process using non-local response functions that intrinsically include all multipoles. We present a semi-classical approach for calculating non-local response functions based on the minimal coupling Hamiltonian. The first, second, and third order response functions are expressed in terms of correlation functions of the charge and the current densities. This approach is based on the gauge invariant current rather than the polarization, and on the vector potential rather than the electric and magnetic fields. PMID:26520498

  14. Local and global effects of the cross-field current instability

    NASA Technical Reports Server (NTRS)

    Lui, A. T. Y.

    1996-01-01

    The cross-field current instability (CCI) was proposed elsewhere as a plausible mechanism for the initiation and intensification of substorm expansions. This instability encompasses the modified two stream, the ion-Weibel and the lower hybrid drift modes. The work carried out in relation to this instability and its local and global effects is reviewed. Predicted local effects include current reduction, particle acceleration, the excitation of oblique whistlers and lower hybrid drift waves, and the breakdown of the frozen-in-field condition through anomalous dissipation. The predicted global effects of CCI include the offset of force equilibrium and the generation of field aligned currents at the disruption site, which allow the efficient large scale transportation of mass, momentum and energy within the magnetosphere.

  15. Intercultural Interactions of Mono-Cultural, Mono-Lingual Local Students in Small Group Learning Activities: A Bourdieusian Analysis

    ERIC Educational Resources Information Center

    Colvin, Cassandra; Fozdar, Farida; Volet, Simone

    2015-01-01

    This research examines the understandings and experiences of mono-cultural, mono-lingual local students in relation to intercultural interactions within small group learning activities at university. Bourdieu's concepts of field, habitus and capital are employed to illuminate a number of barriers to intercultural interaction. Using qualitative…

  16. Protease activity, localization and inhibition in the human hair follicle

    PubMed Central

    Bhogal, R K; Mouser, P E; Higgins, C A; Turner, G A

    2014-01-01

    Synopsis Objective In humans, the process of hair shedding, referred to as exogen, is believed to occur independently of the other hair cycle phases. Although the actual mechanisms involved in hair shedding are not fully known, it has been hypothesized that the processes leading to the final step of hair shedding may be driven by proteases and/or protease inhibitor activity. In this study, we investigated the presence of proteases and protease activity in naturally shed human hairs and assessed enzyme inhibition activity of test materials. Methods We measured enzyme activity using a fluorescence-based assay and protein localization by indirect immunohistochemistry (IHC). We also developed an ex vivo skin model for measuring the force required to pull hair fibres from skin. Results Our data demonstrate the presence of protease activity in the tissue material surrounding club roots. We also demonstrated the localization of specific serine protease protein expression in human hair follicle by IHC. These data provide evidence demonstrating the presence of proteases around the hair club roots, which may play a role during exogen. We further tested the hypothesis that a novel protease inhibitor system (combination of Trichogen® and climbazole) could inhibit protease activity in hair fibre club root extracts collected from a range of ethnic groups (UK, Brazil, China, first-generation Mexicans in the USA, Thailand and Turkey) in both males and females. Furthermore, we demonstrated that this combination is capable of increasing the force required to remove hair in an ex vivo skin model system. Conclusion These studies indicate the presence of proteolytic activity in the tissue surrounding the human hair club root and show that it is possible to inhibit this activity with a combination of Trichogen® and climbazole. This technology may have potential to reduce excessive hair shedding. Résumé Objectif Chez l'homme, le processus de perte de cheveux, désigné comme exog

  17. [Influence of Medication on the Oscillatory and Dynamic Characteristics of Subthalamic Local Field Potentials in Patients with Parkinson's Disease].

    PubMed

    Wang, Yanan; Geng, Xinyi; Huang, Yongzhi; Wang, Shouyan

    2016-02-01

    The dysfunction of subthalamic nucleus is the main cause of Parkinson's disease. Local field potentials in human subthalamic nucleus contain rich physiological information. The present study aimed to quantify the oscillatory and dynamic characteristics of local field potentials of subthalamic nucleus, and their modulation by the medication therapy for Parkinson's disease. The subthalamic nucleus local field potentials were recorded from patients with Parkinson's disease at the states of on and off medication. The oscillatory features were characterised with the power spectral analysis. Furthermore, the dynamic features were characterised with time-frequency analysis and the coefficient of variation measure of the time-variant power at each frequency. There was a dominant peak at low beta-band with medication off. The medication significantly suppressed the low beta component and increased the theta component. The amplitude fluctuation of neural oscillations was measured by the coefficient of variation. The coefficient of variation in 4-7 Hz and 60-66 Hz was increased by medication. These effects proved that medication had significant modulation to subthalamic nucleus neural oscillatory synchronization and dynamic features. The subthalamic nucleus neural activities tend towards stable state under medication. The findings would provide quantitative biomarkers for studying the mechanisms of Parkinson's disease and clinical treatments of medication or deep brain stimulation. PMID:27382739

  18. Time and Frequency-Dependent Modulation of Local Field Potential Synchronization by Deep Brain Stimulation

    PubMed Central

    McCracken, Clinton B.; Kiss, Zelma H. T.

    2014-01-01

    High-frequency electrical stimulation of specific brain structures, known as deep brain stimulation (DBS), is an effective treatment for movement disorders, but mechanisms of action remain unclear. We examined the time-dependent effects of DBS applied to the entopeduncular nucleus (EP), the rat homolog of the internal globus pallidus, a target used for treatment of both dystonia and Parkinson’s disease (PD). We performed simultaneous multi-site local field potential (LFP) recordings in urethane-anesthetized rats to assess the effects of high-frequency (HF, 130 Hz; clinically effective), low-frequency (LF, 15 Hz; ineffective) and sham DBS delivered to EP. LFP activity was recorded from dorsal striatum (STR), ventroanterior thalamus (VA), primary motor cortex (M1), and the stimulation site in EP. Spontaneous and acute stimulation-induced LFP oscillation power and functional connectivity were assessed at baseline, and after 30, 60, and 90 minutes of stimulation. HF EP DBS produced widespread alterations in spontaneous and stimulus-induced LFP oscillations, with some effects similar across regions and others occurring in a region- and frequency band-specific manner. Many of these changes evolved over time. HF EP DBS produced an initial transient reduction in power in the low beta band in M1 and STR; however, phase synchronization between these regions in the low beta band was markedly suppressed at all time points. DBS also enhanced low gamma synchronization throughout the circuit. With sustained stimulation, there were significant reductions in low beta synchronization between M1-VA and STR-VA, and increases in power within regions in the faster frequency bands. HF DBS also suppressed the ability of acute EP stimulation to induce beta oscillations in all regions along the circuit. This dynamic pattern of synchronizing and desynchronizing effects of EP DBS suggests a complex modulation of activity along cortico-BG-thalamic circuits underlying the therapeutic effects

  19. Phase Locking of Multiple Single Neurons to the Local Field Potential in Cat V1.

    PubMed

    Martin, Kevan A C; Schröder, Sylvia

    2016-02-24

    The local field potential (LFP) is thought to reflect a temporal reference for neuronal spiking, which may facilitate information coding and orchestrate the communication between neural populations. To explore this proposed role, we recorded the LFP and simultaneously the spike activity of one to three nearby neurons in V1 of anesthetized cats during the presentation of drifting sinusoidal gratings, binary dense noise stimuli, and natural movies. In all stimulus conditions and during spontaneous activity, the average LFP power at frequencies >20 Hz was higher when neurons were spiking versus not spiking. The spikes were weakly but significantly phase locked to all frequencies of the LFP. The average spike phase of the LFP was stable across high and low levels of LFP power, but the strength of phase locking at low frequencies (≤10 Hz) increased with increasing LFP power. In a next step, we studied how strong stimulus responses of single neurons are reflected in the LFP and the LFP-spike relationship. We found that LFP power was slightly increased and phase locking was slightly stronger during strong compared with weak stimulus-locked responses. In summary, the coupling strength between high frequencies of the LFP and spikes was not strongly modulated by LFP power, which is thought to reflect spiking synchrony, nor was it strongly influenced by how strongly the neuron was driven by the stimulus. Furthermore, a comparison between neighboring neurons showed no clustering of preferred LFP phase. We argue that hypotheses on the relevance of phase locking in their current form are inconsistent with our findings. PMID:26911695

  20. Long term, stable brain machine interface performance using local field potentials and multiunit spikes

    NASA Astrophysics Data System (ADS)

    Flint, Robert D.; Wright, Zachary A.; Scheid, Michael R.; Slutzky, Marc W.

    2013-10-01

    Objective. Brain machine interfaces (BMIs) have the potential to restore movement to people with paralysis. However, a clinically-viable BMI must enable consistently accurate control over time spans ranging from years to decades, which has not yet been demonstrated. Most BMIs that use single-unit spikes as inputs will experience degraded performance over time without frequent decoder re-training. Two other signals, local field potentials (LFPs) and multi-unit spikes (MSPs), may offer greater reliability over long periods and better performance stability than single-unit spikes. Here, we demonstrate that LFPs can be used in a biomimetic BMI to control a computer cursor. Approach. We implanted two rhesus macaques with intracortical microelectrodes in primary motor cortex. We recorded LFP and MSP signals from the monkeys while they performed a continuous reaching task, moving a cursor to randomly-placed targets on a computer screen. We then used the LFP and MSP signals to construct biomimetic decoders for control of the cursor. Main results. Both monkeys achieved high-performance, continuous control that remained stable or improved over nearly 12 months using an LFP decoder that was not retrained or adapted. In parallel, the monkeys used MSPs to control a BMI without retraining or adaptation and had similar or better performance, and that predominantly remained stable over more than six months. In contrast to their stable online control, both LFP and MSP signals showed substantial variability when used offline to predict hand movements. Significance. Our results suggest that the monkeys were able to stabilize the relationship between neural activity and cursor movement during online BMI control, despite variability in the relationship between neural activity and hand movements.

  1. Local energy and power in many-particle quantum systems driven by an external electrical field

    NASA Astrophysics Data System (ADS)

    Albareda, Guillermo; Traversa, Fabio Lorenzo; Oriols, Xavier

    2016-05-01

    We derive expressions for the expectation values of the local energy and the local power for a many-particle system of (scalar) charged particles interacting with an external electrical field. In analogy with the definition of the (local) current probability density, we construct a local energy operator such that the time-rate of change of its expectation value provides information on the spatial distribution of power. Results are presented as functions of an arbitrarily small volume Ω , and physical insights are discussed by means of the quantum hydrodynamical representation of the wavefunction, which is proven to allow for a clear-cut separation into contributions with and without classical correspondence. Quantum features of the local power are mainly manifested through the presence of non-local sources/sinks of power and through the action of forces with no classical counterpart. Many-particle classical-like effects arise in the form of current-force correlations and through the inflow/outflow of energy across the boundaries of the volume Ω . Interestingly, all these intriguing features are only reflected in the expression of the local power when the volume Ω is finite. Otherwise, for closed systems with Ω \\to ∞ , we recover a classical-like single-particle expression.

  2. Local field potential correlates of auditory working memory in primate dorsal temporal pole.

    PubMed

    Bigelow, James; Ng, Chi-Wing; Poremba, Amy

    2016-06-01

    Dorsal temporal pole (dTP) is a cortical region at the rostral end of the superior temporal gyrus that forms part of the ventral auditory object processing pathway. Anatomical connections with frontal and medial temporal areas, as well as a recent single-unit recording study, suggest this area may be an important part of the network underlying auditory working memory (WM). To further elucidate the role of dTP in auditory WM, local field potentials (LFPs) were recorded from the left dTP region of two rhesus macaques during an auditory delayed matching-to-sample (DMS) task. Sample and test sounds were separated by a 5-s retention interval, and a behavioral response was required only if the sounds were identical (match trials). Sensitivity of auditory evoked responses in dTP to behavioral significance and context was further tested by passively presenting the sounds used as auditory WM memoranda both before and after the DMS task. Average evoked potentials (AEPs) for all cue types and phases of the experiment comprised two small-amplitude early onset components (N20, P40), followed by two broad, large-amplitude components occupying the remainder of the stimulus period (N120, P300), after which a final set of components were observed following stimulus offset (N80OFF, P170OFF). During the DMS task, the peak amplitude and/or latency of several of these components depended on whether the sound was presented as the sample or test, and whether the test matched the sample. Significant differences were also observed among the DMS task and passive exposure conditions. Comparing memory-related effects in the LFP signal with those obtained in the spiking data raises the possibility some memory-related activity in dTP may be locally produced and actively generated. The results highlight the involvement of dTP in auditory stimulus identification and recognition and its sensitivity to the behavioral significance of sounds in different contexts. This article is part of a Special

  3. An active role for magnetic fields in solar flares

    NASA Technical Reports Server (NTRS)

    Rust, D. M.

    1976-01-01

    Observations of photospheric magnetic fields are reviewed to determine whether changes in such fields can be related to flare activity, assuming that magnetic fields play an active role in providing flare energy. An intimate relation between emerging fields and bright flare knots is noted, and it is shown that the activation and eruption of an H-alpha filament is indicative of a major disruption of a magnetic field just prior to a flare. Observations of twisting motions in a filament just before a flare are discussed, erupting untwisting filaments are taken as unambiguous evidence for restructuring of the magnetic fields associated with flares, and it is argued that magnetic-field changes in the midst of most flares are obvious. It is concluded that successive brightenings in a family of loops may be evidence for the spread of a magnetic-field reconnection point from one field concentration to another and that flares may well take place in regions of field-line reconnection. This latter conclusion is illustrated using an empirical flare model that involves field-line reconnection, filament activation, and emerging magnetic flux.

  4. Nonlocal and local magnetization dynamics excited by an RF magnetic field in magnetic multilayers

    NASA Astrophysics Data System (ADS)

    Moriyama, Takahiro

    A microwave study in spintronic devices has been actively pursued in the past several years due to the fertile physics and potential applications. On one hand, a passive use of microwave can be very helpful to analyze and understand the magnetization dynamics in spintronic devices. Examples include ferromagnetic resonance (FMR) measurements, and various microwave spectrum analyses in ferromagnetic materials. The most important chrematistic parameter for the phenomenological analysis on the magnetization dynamics is, so called, the Gilbert damping constant. In this work, a relatively new measurement technique, a flip-chip FMR measurement, to conduct the ferromagnetic resonance measurements has been developed. The measurement technique is equally comparable to a conventional FMR measurement. The Gilbert damping constants were extracted for single ferromagnetic layer, spin vale structures, and magnetic tunnel junctions (MTJs). On the other hand, an active use of microwave yields a great potential for interesting phenomena which give new functionalities into spintronic devices. For instance, a spin wave excitation by an rf field can be used to reduce the switching field of a ferromagnet, i.e. microwave assisted magnetization reversal, which could be a potential application in advanced recording media. More interestingly, a precessing magnetization driven by an rf field can generate a pure spin current into a neighboring layer, i.e. spin pumping effect, which is one of the candidates for generating a pure spin current. A ferromagnetic tunnel junction (MTJ) is one of the important devices in spintronics, which is also the key device to investigate the local and nonlocal magnetization dynamics in this work. Therefore, it is also important to develop high quality MTJs. My work starts from the development of MTJ with AlOx and MgO tunnel barriers where it was found it is crucial to find the proper condition for forming a few nanometers thick tunnel barrier. After obtaining

  5. Near-field optical patterning and structuring based on local-field enhancement at the extremity of a metal tip.

    PubMed

    Royer, Pascal; Barchiesi, Dominique; Lerondel, Gilles; Bachelot, Renaud

    2004-04-15

    We present a particular approach and the associated results allowing the nanostructuration of a thin photosensitive polymer film. This approach based on a scanning near-field optical microscopy configuration uses the field-enhancement (FE) effect, a so-called lightning-rod effect appearing at the extremity of a metallic tip when illuminated with an incident light polarized along the tip axis. The local enhancement of the electromagnetic field straight below the tip's apex is observed directly through a photoisomerization reaction, inducing the growth of a topographical nanodot characterized in situ by atomic-force microscopy using the same probe. From a survey of the literature, we first review the different experimental approaches offered to nanostructure materials by near-field optical techniques. We describe more particularly the FE effect approach. An overview of the theoretical approach of this effect is then given before presenting some experimental results so as theoretical results using the finite-element method. These results show the influence on the nanostructuration of the polymer of a few experimental parameters such as the polarization state, the illumination mode and the tip's geometry. Finally, the potentiality of this technique for some applications in the field of lithography and high-density data storage is shown via the fabrication of nano-patterns. PMID:15306496

  6. Local field enhancement on demand based on hybrid plasmonic-dielectric directional coupler.

    PubMed

    Adhem, Kholod; Avrutsky, Ivan

    2016-03-21

    The concept of local field enhancement using conductor-gap-dielectric-substrate (CGDS) waveguide structure is proposed. The dispersion equation is derived analytically and solved numerically. The solution of the dispersion equation reveals the anti-crossing behavior of coupled modes. the optimal gap layer thickness and the coupling length of the guided modes are obtained. The mechanism of the CGDS works as follows: Light waves are guided by conventional low-loss dielectric waveguides and, upon demand, they are transformed into highly confined plasmonic modes with strong local field enhancement, and get transformed back into low-loss dielectric modes. As an example, in a representative CGDS structure, the optimal plasmonic gap size is 17 nm, the local light intensity is found to be more than one order of magnitude stronger than the intensity of the dielectric mode at the film surface. The coupling length is only 2.1 μm at a wavelength of 632.8 nm. Such a local field confinement on demand is expected to facilitate efficient light-matter interaction in integrated photonic devices while minimizing losses typical for plasmonic structures. PMID:27136767

  7. Effect of the local morphology in the field emission properties of conducting polymer surfaces

    NASA Astrophysics Data System (ADS)

    de Assis, T. A.; Benito, R. M.; Losada, J. C.; Andrade, R. F. S.; Miranda, J. G. V.; de Souza, Nara C.; de Castilho, C. M. C.; Mota, F. de B.; Borondo, F.

    2013-07-01

    In this work, we present systematic theoretical evidence of a relationship between the point local roughness exponent (PLRE) (which quantifies the heterogeneity of an irregular surface) and the cold field emission properties (indicated by the local current density and the macroscopic current density) of real polyaniline (PANI) surfaces, considered nowadays as very good candidates in the design of field emission devices. The latter are obtained from atomic force microscopy data. The electric field and potential are calculated in a region bounded by the rough PANI surface and a distant plane, both boundaries held at distinct potential values. We numerically solve Laplace’s equation subject to appropriate Dirichlet’s condition. Our results show that local roughness reveals the presence of specific sharp emitting spots with a smooth geometry, which are the main ones responsible (but not the only) for the emission efficiency of such surfaces for larger deposition times. Moreover, we have found, with a proper choice of a scale interval encompassing the experimentally measurable average grain length, a highly structured dependence of local current density on PLRE, considering different ticks of PANI surfaces.

  8. AdS/CFT and local renormalization group with gauge fields

    NASA Astrophysics Data System (ADS)

    Kikuchi, Ken; Sakai, Tadakatsu

    2016-03-01

    We revisit a study of local renormalization group (RG) with background gauge fields incorporated using the AdS/CFT correspondence. Starting with a (d+1)-dimensional bulk gravity coupled to scalars and gauge fields, we derive a local RG equation from a flow equation by working in the Hamilton-Jacobi formulation of the bulk theory. The Gauss's law constraint associated with gauge symmetry plays an important role. RG flows of the background gauge fields are governed by vector β -functions, and some of their interesting properties are known to follow. We give a systematic rederivation of them on the basis of the flow equation. Fixing an ambiguity of local counterterms in such a manner that is natural from the viewpoint of the flow equation, we determine all the coefficients uniquely appearing in the trace of the stress tensor for d=4. A relation between a choice of schemes and a virial current is discussed. As a consistency check, these are found to satisfy the integrability conditions of local RG transformations. From these results, we are led to a proof of a holographic c-theorem by determining a full family of schemes where a trace anomaly coefficient is related with a holographic c-function.

  9. Relative localization in wireless sensor networks for measurement of electric fields under HVDC transmission lines.

    PubMed

    Cui, Yong; Wang, Qiusheng; Yuan, Haiwen; Song, Xiao; Hu, Xuemin; Zhao, Luxing

    2015-01-01

    In the wireless sensor networks (WSNs) for electric field measurement system under the High-Voltage Direct Current (HVDC) transmission lines, it is necessary to obtain the electric field distribution with multiple sensors. The location information of each sensor is essential to the correct analysis of measurement results. Compared with the existing approach which gathers the location information by manually labelling sensors during deployment, the automatic localization can reduce the workload and improve the measurement efficiency. A novel and practical range-free localization algorithm for the localization of one-dimensional linear topology wireless networks in the electric field measurement system is presented. The algorithm utilizes unknown nodes' neighbor lists based on the Received Signal Strength Indicator (RSSI) values to determine the relative locations of nodes. The algorithm is able to handle the exceptional situation of the output permutation which can effectively improve the accuracy of localization. The performance of this algorithm under real circumstances has been evaluated through several experiments with different numbers of nodes and different node deployments in the China State Grid HVDC test base. Results show that the proposed algorithm achieves an accuracy of over 96% under different conditions. PMID:25658390

  10. A microscopic field theoretical approach for active systems

    NASA Astrophysics Data System (ADS)

    Alaimo, F.; Praetorius, S.; Voigt, A.

    2016-08-01

    We consider a microscopic modeling approach for active systems. The approach extends the phase field crystal (PFC) model and allows us to describe generic properties of active systems within a continuum model. The approach is validated by reproducing results obtained with corresponding agent-based and microscopic phase field models. We consider binary collisions, collective motion and vortex formation. For larger numbers of particles we analyze the coarsening process in active crystals and identify giant number fluctuation in a cluster formation process.

  11. Self-localized and self-constricted electromagnetic field in plasma and atmosphere

    NASA Astrophysics Data System (ADS)

    Alanakyan, Yu. R.

    2016-05-01

    A possibility of creation of a super-high-frequency electromagnetic-field clot in the plasma is shown. Two cases of the field self-localization in the plasma are considered. In the first case, a super-high-frequency electric field creates an annular channel by displacing the plasma and induces a curl-like magnetic field inside. In the second case, the electric field creates a toroidal channel where different field structures are possible. For example, the magnetic lines of the force are aligned along the big circle of the torus, while the curl-like electric lines are aligned along the small circle. Otherwise, the magnetic field is curl-like and the electric-field lines are aligned along the big circle. We evaluate the electric field energy that is required for a curl-like structure of about 3 cm in size to exist during 10 s in the atmospheric air. This energy sustains plasma in the vicinity of the curl-like area.

  12. The Split Property for Locally Covariant Quantum Field Theories in Curved Spacetime

    NASA Astrophysics Data System (ADS)

    Fewster, Christopher J.

    2015-12-01

    The split property expresses the way in which local regions of spacetime define subsystems of a quantum field theory. It is known to hold for general theories in Minkowski space under the hypothesis of nuclearity. Here, the split property is discussed for general locally covariant quantum field theories in arbitrary globally hyperbolic curved spacetimes, using a spacetime deformation argument to transport the split property from one spacetime to another. It is also shown how states obeying both the split and (partial) Reeh-Schlieder properties can be constructed, providing standard split inclusions of certain local von Neumann algebras. Sufficient conditions are given for the theory to admit such states in ultrastatic spacetimes, from which the general case follows. A number of consequences are described, including the existence of local generators for global gauge transformations, and the classification of certain local von Neumann algebras. Similar arguments are applied to the distal split property and circumstances are exhibited under which distal splitting implies the full split property.

  13. Intrinsic Localized Modes in Quantum Ferromagnetic XXZ Chains in an Oblique Magnetic Field

    NASA Astrophysics Data System (ADS)

    Li, De-Jun

    2016-02-01

    A semiclassical study of intrinsic localized spin-wave modes in a one-dimensional quantum ferromagnetic XXZ chain in an oblique magnetic field is presented in this paper. We quantize the model Hamiltonian by introducing the Dyson-Maleev transformation, and adopt the coherent state representation as the basic representation of the system. By means of the method of multiple scales combined with a quasidiscreteness approximation, the equation of motion for the coherent-state amplitude can be reduced to the standard nonlinear Schrödinger equation. It is found that, at the center of the Brillouin zone, when θ < θ c a bright intrinsic localized spin-wave mode appears below the bottom of the magnon frequency band and when θ > θ c a dark intrinsic localized spin-wave resonance mode can occur above the bottom of the magnon frequency band. In other words, the switch between the bright and dark intrinsic localized spin-wave modes can be controlled via varying the angle of the magnetic field. This result has potential applications in quantum information storage. In addition, we find that, at the boundary of the Brillouin zone, the system can only produce a dark intrinsic localized spin-wave mode, whose eigenfrequency is above the upper of the magnon frequency band.

  14. High Accuracy Passive Magnetic Field-Based Localization for Feedback Control Using Principal Component Analysis.

    PubMed

    Foong, Shaohui; Sun, Zhenglong

    2016-01-01

    In this paper, a novel magnetic field-based sensing system employing statistically optimized concurrent multiple sensor outputs for precise field-position association and localization is presented. This method capitalizes on the independence between simultaneous spatial field measurements at multiple locations to induce unique correspondences between field and position. This single-source-multi-sensor configuration is able to achieve accurate and precise localization and tracking of translational motion without contact over large travel distances for feedback control. Principal component analysis (PCA) is used as a pseudo-linear filter to optimally reduce the dimensions of the multi-sensor output space for computationally efficient field-position mapping with artificial neural networks (ANNs). Numerical simulations are employed to investigate the effects of geometric parameters and Gaussian noise corruption on PCA assisted ANN mapping performance. Using a 9-sensor network, the sensing accuracy and closed-loop tracking performance of the proposed optimal field-based sensing system is experimentally evaluated on a linear actuator with a significantly more expensive optical encoder as a comparison. PMID:27529253

  15. Generator localization by current source density (CSD): implications of volume conduction and field closure at intracranial and scalp resolutions.

    PubMed

    Tenke, Craig E; Kayser, Jürgen

    2012-12-01

    The topographic ambiguity and reference-dependency that has plagued EEG/ERP research throughout its history are largely attributable to volume conduction, which may be concisely described by a vector form of Ohm's Law. This biophysical relationship is common to popular algorithms that infer neuronal generators via inverse solutions. It may be further simplified as Poisson's source equation, which identifies underlying current generators from estimates of the second spatial derivative of the field potential (Laplacian transformation). Intracranial current source density (CSD) studies have dissected the "cortical dipole" into intracortical sources and sinks, corresponding to physiologically-meaningful patterns of neuronal activity at a sublaminar resolution, much of which is locally cancelled (i.e., closed field). By virtue of the macroscopic scale of the scalp-recorded EEG, a surface Laplacian reflects the radial projections of these underlying currents, representing a unique, unambiguous measure of neuronal activity at scalp. Although the surface Laplacian requires minimal assumptions compared to complex, model-sensitive inverses, the resulting waveform topographies faithfully summarize and simplify essential constraints that must be placed on putative generators of a scalp potential topography, even if they arise from deep or partially-closed fields. CSD methods thereby provide a global empirical and biophysical context for generator localization, spanning scales from intracortical to scalp recordings. PMID:22796039

  16. 24 CFR 1000.240 - When is a local cooperation agreement required for affordable housing activities?

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 24 Housing and Urban Development 4 2010-04-01 2010-04-01 false When is a local cooperation... ACTIVITIES Indian Housing Plan (IHP) § 1000.240 When is a local cooperation agreement required for affordable housing activities? The requirement for a local cooperation agreement applies only to rental and...

  17. Spin dynamics under local gauge fields in chiral spin-orbit coupling systems

    SciTech Connect

    Tan, S.G.; Jalil, M.B.A.; Fujita, T.; Liu, X.J.

    2011-02-15

    Research Highlights: > We derive a modified LLG equation in magnetic systems with spin-orbit coupling (SOC). > Our results are applied to magnetic multilayers, and DMS and magnetic Rashba systems. > SOC mediated magnetization switching is predicted in rare earth metals (large SOC). > The magnetization trajectory and frequency can be modulated by applied voltage. > This facilitates potential application as tunable microwave oscillators. - Abstract: We present a theoretical description of local spin dynamics in magnetic systems with a chiral spin texture and finite spin-orbit coupling (SOC). Spin precession about the relativistic effective magnetic field in a SOC system gives rise to a non-Abelian SU(2) gauge field reminiscent of the Yang-Mills field. In addition, the adiabatic relaxation of electron spin along the local spin yields an U(1) x U(1) topological gauge (Berry) field. We derive the corresponding equation of motion i.e. modified Landau-Lifshitz-Gilbert (LLG) equation, for the local spin under the influence of these effects. Focusing on the SU(2) gauge, we obtain the spin torque magnitude, and the amplitude and frequency of spin oscillations in this system. Our theoretical estimates indicate significant spin torque and oscillations in systems with large spin-orbit coupling, which may be utilized in technological applications such as current-induced magnetization-switching and tunable microwave oscillators.

  18. Rapid tsunami models and earthquake source parameters: Far-field and local applications

    USGS Publications Warehouse

    Geist, E.L.

    2005-01-01

    Rapid tsunami models have recently been developed to forecast far-field tsunami amplitudes from initial earthquake information (magnitude and hypocenter). Earthquake source parameters that directly affect tsunami generation as used in rapid tsunami models are examined, with particular attention to local versus far-field application of those models. First, validity of the assumption that the focal mechanism and type of faulting for tsunamigenic earthquakes is similar in a given region can be evaluated by measuring the seismic consistency of past events. Second, the assumption that slip occurs uniformly over an area of rupture will most often underestimate the amplitude and leading-wave steepness of the local tsunami. Third, sometimes large magnitude earthquakes will exhibit a high degree of spatial heterogeneity such that tsunami sources will be composed of distinct sub-events that can cause constructive and destructive interference in the wavefield away from the source. Using a stochastic source model, it is demonstrated that local tsunami amplitudes vary by as much as a factor of two or more, depending on the local bathymetry. If other earthquake source parameters such as focal depth or shear modulus are varied in addition to the slip distribution patterns, even greater uncertainty in local tsunami amplitude is expected for earthquakes of similar magnitude. Because of the short amount of time available to issue local warnings and because of the high degree of uncertainty associated with local, model-based forecasts as suggested by this study, direct wave height observations and a strong public education and preparedness program are critical for those regions near suspected tsunami sources.

  19. Coulomb's law corrections and fermion field localization in a tachyonic de Sitter thick braneworld

    NASA Astrophysics Data System (ADS)

    Cartas-Fuentevilla, Roberto; Escalante, Alberto; Germán, Gabriel; Herrera-Aguilar, Alfredo; Rigel Mora-Luna, Refugio

    2016-05-01

    Following recent studies which show that it is possible to localize gravity as well as scalar and gauge vector fields in a tachyonic de Sitter thick braneworld, we investigate the solution of the gauge hierarchy problem, the localization of fermion fields in this model, the recovering of the Coulomb law on the non-relativistic limit of the Yukawa interaction between bulk fermions and gauge bosons localized in the brane, and confront the predicted 5D corrections to the photon mass with its upper experimental/observational bounds, finding the model physically viable since it passes these tests. In order to achieve the latter aims we first consider the Yukawa interaction term between the fermionic and the tachyonic scalar fields MF(T)ΨΨ̅ in the action and analyze four distinct tachyonic functions F(T) that lead to four different structures of the respective fermionic mass spectra with different physics. In particular, localization of the massless left-chiral fermion zero mode is possible for three of these cases. We further analyze the phenomenology of these Yukawa interactions among fermion fields and gauge bosons localized on the brane and obtain the crucial and necessary information to compute the corrections to Coulomb's law coming from massive KK vector modes in the non-relativistic limit. These corrections are exponentially suppressed due to the presence of the mass gap in the mass spectrum of the bulk gauge vector field. From our results we conclude that corrections to Coulomb's law in the thin brane limit have the same form (up to a numerical factor) as far as the left-chiral massless fermion field is localized on the brane. Finally we compute the corrections to the Coulomb's law for an arbitrarily thick brane scenario which can be interpreted as 5D corrections to the photon mass. By performing consistent estimations with brane phenomenology, we found that the predicted corrections to the photon mass, which are well bounded by the experimentally observed or

  20. Field calibration of PADC track etch detectors for local neutron dosimetry in man using different radiation qualities

    NASA Astrophysics Data System (ADS)

    Hälg, Roger A.; Besserer, Jürgen; Boschung, Markus; Mayer, Sabine; Clasie, Benjamin; Kry, Stephen F.; Schneider, Uwe

    2012-12-01

    In order to quantify the dose from neutrons to a patient for contemporary radiation treatment techniques, measurements inside phantoms, representing the patient, are necessary. Published reports on neutron dose measurements cover measurements performed free in air or on the surface of phantoms and the doses are expressed in terms of personal dose equivalent or ambient dose equivalent. This study focuses on measurements of local neutron doses inside a radiotherapy phantom and presents a field calibration procedure for PADC track etch detectors. An initial absolute calibration factor in terms of Hp(10) for personal dosimetry is converted into neutron dose equivalent and additional calibration factors are derived to account for the spectral changes in the neutron fluence for different radiation therapy beam qualities and depths in the phantom. The neutron spectra used for the calculation of the calibration factors are determined in different depths by Monte Carlo simulations for the investigated radiation qualities. These spectra are used together with the energy dependent response function of the PADC detectors to account for the spectral changes in the neutron fluence. The resulting total calibration factors are 0.76 for a photon beam (in- and out-of-field), 1.00 (in-field) and 0.84 (out-of-field) for an active proton beam and 1.05 (in-field) and 0.91 (out-of-field) for a passive proton beam, respectively. The uncertainty for neutron dose measurements using this field calibration method is less than 40%. The extended calibration procedure presented in this work showed that it is possible to use PADC track etch detectors for measurements of local neutron dose equivalent inside anthropomorphic phantoms by accounting for spectral changes in the neutron fluence.

  1. Formation of active region and quiescent prominence magnetic field configurations

    NASA Technical Reports Server (NTRS)

    An, C.-H.; Bao, J. J.; Wu, S. T.

    1986-01-01

    To investigate the formation of prominences, researchers studied chromospheric mass injection into an overlying coronal dipole magnetic field using a 2-D ideal magnetohydrodynamic (MHD) numerical model. Researchers propose that active region prominences are formed by chromospheric plasmas injected directly into the overlying coronal magnetic field and that quiescent prominences are formed by plasmas evaporated at the interface between spicules and corona. Hence, for the simulation of an active region prominence magnetic field we inject the mass from one side, but use a symmetric mass injection to form a quiescent prominence field configuration. Researchers try to find optimum conditions for the formation of Kippenhahn-Schuluter(K-S)type field configuration for stable support of the injection plasmas. They find that the formation of K-S type field configuration by mass injection requires a delicate balance between injection velocity, density, and overlying magnetic fields. These results may explain why a prominence does not form on every neutral line.

  2. Full-Field Strain Measurement On Titanium Welds And Local Elasto-Plastic Identification With The Virtual Fields Method

    SciTech Connect

    Tattoli, F.; Casavola, C.; Pierron, F.; Rotinat, R.; Pappalettere, C.

    2011-01-17

    One of the main problems in welding is the microstructural transformation within the area affected by the thermal history. The resulting heterogeneous microstructure within the weld nugget and the heat affected zones is often associated with changes in local material properties. The present work deals with the identification of material parameters governing the elasto--plastic behaviour of the fused and heat affected zones as well as the base material for titanium hybrid welded joints (Ti6Al4V alloy). The material parameters are identified from heterogeneous strain fields with the Virtual Fields Method. This method is based on a relevant use of the principle of virtual work and it has been shown to be useful and much less time consuming than classical finite element model updating approaches applied to similar problems. The paper will present results and discuss the problem of selection of the weld zones for the identification.

  3. The Life Cycle of Active Region Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Cheung, M. C. M.; van Driel-Gesztelyi, L.; Martínez Pillet, V.; Thompson, M. J.

    2016-08-01

    We present a contemporary view of how solar active region magnetic fields are understood to be generated, transported and dispersed. Empirical trends of active region properties that guide model development are discussed. Physical principles considered important for active region evolution are introduced and advances in modeling are reviewed.

  4. Public hearing or 'hearing public'? an evaluation of the participation of local stakeholders in environmental impact assessment of Ghana's Jubilee oil fields.

    PubMed

    Bawole, Justice Nyigmah

    2013-08-01

    This article investigates the involvement of local stakeholders in the environmental impact assessment (EIA) processes of Ghana's first off-shore oil fields (the Jubilee fields). Adopting key informants interviews and documentary reviews, the article argues that the public hearings and the other stakeholder engagement processes were cosmetic and rhetoric with the view to meeting legal requirements rather than a purposeful interest in eliciting inputs from local stakeholders. It further argues that the operators appear to lack the social legitimacy and social license that will make them acceptable in the project communities. A rigorous community engagement along with a commitment to actively involving local stakeholders in the corporate social responsibility (CSR) programmes of the partners may enhance the image of the partners and improve their social legitimacy. Local government agencies should be capacitated to actively engage project organisers; and government must mitigate the impact of the oil projects through well-structured social support programmes. PMID:23716010

  5. Public Hearing or `Hearing Public'? An Evaluation of the Participation of Local Stakeholders in Environmental Impact Assessment of Ghana's Jubilee Oil Fields

    NASA Astrophysics Data System (ADS)

    Bawole, Justice Nyigmah

    2013-08-01

    This article investigates the involvement of local stakeholders in the environmental impact assessment (EIA) processes of Ghana's first off-shore oil fields (the Jubilee fields). Adopting key informants interviews and documentary reviews, the article argues that the public hearings and the other stakeholder engagement processes were cosmetic and rhetoric with the view to meeting legal requirements rather than a purposeful interest in eliciting inputs from local stakeholders. It further argues that the operators appear to lack the social legitimacy and social license that will make them acceptable in the project communities. A rigorous community engagement along with a commitment to actively involving local stakeholders in the corporate social responsibility (CSR) programmes of the partners may enhance the image of the partners and improve their social legitimacy. Local government agencies should be capacitated to actively engage project organisers; and government must mitigate the impact of the oil projects through well-structured social support programmes.

  6. Active local control of propeller-aircraft run-up noise.

    PubMed

    Hodgson, Murray; Guo, Jingnan; Germain, Pierre

    2003-12-01

    Engine run-ups are part of the regular maintenance schedule at Vancouver International Airport. The noise generated by the run-ups propagates into neighboring communities, disturbing the residents. Active noise control is a potentially cost-effective alternative to passive methods, such as enclosures. Propeller aircraft generate low-frequency tonal noise that is highly compatible with active control. This paper presents a preliminary investigation of the feasibility and effectiveness of controlling run-up noise from propeller aircraft using local active control. Computer simulations for different configurations of multi-channel active-noise-control systems, aimed at reducing run-up noise in adjacent residential areas using a local-control strategy, were performed. These were based on an optimal configuration of a single-channel control system studied previously. The variations of the attenuation and amplification zones with the number of control channels, and with source/control-system geometry, were studied. Here, the aircraft was modeled using one or two sources, with monopole or multipole radiation patterns. Both free-field and half-space conditions were considered: for the configurations studied, results were similar in the two cases. In both cases, large triangular quiet zones, with local attenuations of 10 dB or more, were obtained when nine or more control channels were used. Increases of noise were predicted outside of these areas, but these were minimized as more control channels were employed. By combining predicted attenuations with measured noise spectra, noise levels after implementation of an active control system were estimated. PMID:14714802

  7. A diversity of localized timescales in network activity

    PubMed Central

    Chaudhuri, Rishidev; Bernacchia, Alberto; Wang, Xiao-Jing

    2014-01-01

    Neurons show diverse timescales, so that different parts of a network respond with disparate temporal dynamics. Such diversity is observed both when comparing timescales across brain areas and among cells within local populations; the underlying circuit mechanism remains unknown. We examine conditions under which spatially local connectivity can produce such diverse temporal behavior. In a linear network, timescales are segregated if the eigenvectors of the connectivity matrix are localized to different parts of the network. We develop a framework to predict the shapes of localized eigenvectors. Notably, local connectivity alone is insufficient for separate timescales. However, localization of timescales can be realized by heterogeneity in the connectivity profile, and we demonstrate two classes of network architecture that allow such localization. Our results suggest a framework to relate structural heterogeneity to functional diversity and, beyond neural dynamics, are generally applicable to the relationship between structure and dynamics in biological networks. DOI: http://dx.doi.org/10.7554/eLife.01239.001 PMID:24448407

  8. 78 FR 54637 - Agency Information Collection Activities; Comment Request; State Educational Agency, Local...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-09-05

    ... Agency Information Collection Activities; Comment Request; State Educational Agency, Local Educational... information technology. Please note that written comments received in response to this notice will be considered public records. Title of Collection: State Educational Agency, Local Educational Agency,...

  9. Hybrid Matter-Wave-Microwave Solitons Produced by the Local-Field Effect.

    PubMed

    Qin, Jieli; Dong, Guangjiong; Malomed, Boris A

    2015-07-10

    It was recently found that the electric local-field effect (LFE) can lead to a strong coupling of atomic Bose-Einstein condensates (BECs) to off-resonant optical fields. We demonstrate that the magnetic LFE gives rise to a previously unexplored mechanism for coupling a (pseudo-) spinor BEC or fermion gas to microwaves (MWs). We present a theory for the magnetic LFE and find that it gives rise to a short-range attractive interaction between two components of the (pseudo) spinor, and a long-range interaction between them. The latter interaction, resulting from deformation of the magnetic field, is locally repulsive but globally attractive, in sharp contrast with its counterpart for the optical LFE, produced by phase modulation of the electric field. Our analytical results, confirmed by the numerical computations, show that the long-range interaction gives rise to modulational instability of the spatially uniform state, and it creates stable ground states in the form of hybrid matter-wave-microwave solitons (which seem like one-dimensional magnetic monopoles), with a size much smaller than the MW wavelength, even in the presence of arbitrarily strong contact intercomponent repulsion. The setting is somewhat similar to exciton-polaritonic condensates in semiconductor microcavities. The release of matter waves from the soliton may be used for the realization of an atom laser. The analysis also applies to molecular BECs with rotational states coupled by the electric MW field. PMID:26207469

  10. Hybrid Matter-Wave-Microwave Solitons Produced by the Local-Field Effect

    NASA Astrophysics Data System (ADS)

    Qin, Jieli; Dong, Guangjiong; Malomed, Boris A.

    2015-07-01

    It was recently found that the electric local-field effect (LFE) can lead to a strong coupling of atomic Bose-Einstein condensates (BECs) to off-resonant optical fields. We demonstrate that the magnetic LFE gives rise to a previously unexplored mechanism for coupling a (pseudo-) spinor BEC or fermion gas to microwaves (MWs). We present a theory for the magnetic LFE and find that it gives rise to a short-range attractive interaction between two components of the (pseudo) spinor, and a long-range interaction between them. The latter interaction, resulting from deformation of the magnetic field, is locally repulsive but globally attractive, in sharp contrast with its counterpart for the optical LFE, produced by phase modulation of the electric field. Our analytical results, confirmed by the numerical computations, show that the long-range interaction gives rise to modulational instability of the spatially uniform state, and it creates stable ground states in the form of hybrid matter-wave-microwave solitons (which seem like one-dimensional magnetic monopoles), with a size much smaller than the MW wavelength, even in the presence of arbitrarily strong contact intercomponent repulsion. The setting is somewhat similar to exciton-polaritonic condensates in semiconductor microcavities. The release of matter waves from the soliton may be used for the realization of an atom laser. The analysis also applies to molecular BECs with rotational states coupled by the electric MW field.

  11. A photonic-crystal optical antenna for extremely large local-field enhancement.

    PubMed

    Chang, Hyun-Joo; Kim, Se-Heon; Lee, Yong-Hee; Kartalov, Emil P; Scherer, Axel

    2010-11-01

    We propose a novel design of an all-dielectric optical antenna based on photonic-band-gap confinement. Specifically, we have engineered the photonic-crystal dipole mode to have broad spectral response (Q~70) and well-directed vertical-radiation by introducing a plane mirror below the cavity. Considerably large local electric-field intensity enhancement~4,500 is expected from the proposed design for a normally incident planewave. Furthermore, an analytic model developed based on coupled-mode theory predicts that the electric-field intensity enhancement can easily be over 100,000 by employing reasonably high-Q (~10,000) resonators. PMID:21164762

  12. Differential Magnetic Field Shear in an Active Region

    NASA Technical Reports Server (NTRS)

    Schmeider, B.; DeMoulin, P.; Aulanier, G.; Golub, Leon

    1997-01-01

    The three-dimensional extrapolation of magnetic field lines from a magnetogram obtained at Kitt Peak allows us to understand the global structure of the NOAA active region 6718, as observed in X-rays with the Normal Incidence X-ray Telescope (NIXT) and in Ha with the Multichannel Subtractive Double Pass spectrograph (MSDP) in Meudon on 1991 July 11. This active region was in a quiet stage. Bright X-ray loops connect plages having field strengths of approx. 300 G, while H-alpha fibriles connect penumbrae having strong spot fields to the surrounding network. Small, intense X-ray features in the moat region around a large spot, which could be called X-ray-bright points, are due mainly to the emergence of magnetic flux and merging of these fields with surrounding ones. A set of large-scale, sheared X-ray loops is observed in the central part of the active region. Based on the fit between the observed coronal structure and the field configurations (and assuming a linear force-free field), we propose a differential magnetic field shear model for this active region. The decreasing shear in outer portions of the active region may indicate a continual relaxation of the magnetic field to a lower energy state in the progressively older portions of the AR.

  13. Scaling of high-field transport and localized heating in graphene transistors.

    PubMed

    Bae, Myung-Ho; Islam, Sharnali; Dorgan, Vincent E; Pop, Eric

    2011-10-25

    We use infrared thermal imaging and electrothermal simulations to find that localized Joule heating in graphene field-effect transistors on SiO(2) is primarily governed by device electrostatics. Hot spots become more localized (i.e., sharper) as the underlying oxide thickness is reduced, such that the average and peak device temperatures scale differently, with significant long-term reliability implications. The average temperature is proportional to oxide thickness, but the peak temperature is minimized at an oxide thickness of ∼90 nm due to competing electrostatic and thermal effects. We also find that careful comparison of high-field transport models with thermal imaging can be used to shed light on velocity saturation effects. The results shed light on optimizing heat dissipation and reliability of graphene devices and interconnects. PMID:21913673

  14. Quantification of deterministic matched-field source localization error in the face of random model inputs

    NASA Astrophysics Data System (ADS)

    Daly, Peter M.; Hebenstreit, Gerald T.

    2003-04-01

    Deterministic source localization using matched-field processing (MFP) has yielded good results in propagation scenarios where the nonrandom model parameter input assumption is valid. In many shallow water environments, inputs to acoustic propagation models may be better represented using random distributions rather than fixed quantities. One can estimate the negative effect of random source inputs on deterministic MFP by (1) obtaining a realistic statistical representation of a signal model parameter, then (2) using the mean of the parameter as input to the MFP signal model (the so-called ``replica vector''), (3) synthesizing a source signal using multiple realizations of the random parameter, and (4) estimating the source localization error by correlating the synthesized signal vector with the replica vector over a three dimensional space. This approach allows one to quantify deterministic localization error introduced by random model parameters, including sound velocity profile, hydrophone locations, and sediment thickness and speed. [Work supported by DARPA Advanced Technology Office.

  15. Local and global impacts on the fair-weather electric field in Israel

    NASA Astrophysics Data System (ADS)

    Yaniv, Roy; Yair, Yoav; Price, Colin; Katz, Shai

    2016-05-01

    Ground-based measurements of the vertical electric field (Ez or potential gradient) during fair weather days in the Negev desert, southern Israel are presented for the period June 2013-July 2015. We show results of the diurnal variation of Ez on seasonal and annual time scales, and make comparisons with the well-known Carnegie curve. We show a positive correlation between the diurnal Ez values and the number of global thunderstorm clusters on the same days. However, the diurnal Ez curves observed in the Negev desert show a local morning peak (8-10 UT) that is missing from the Carnegie Curve, but observed in other land-based Ez data from around the world. The morning peak is assumed to be a local effect and shown to correlate with a peak in the local aerosol loading in the lower atmosphere due to the increase in turbulence and mixing caused by solar heating in the morning hours.

  16. Long-range orientational order, local-field anisotropy, and mean molecular polarizability in liquid crystals

    SciTech Connect

    Aver'yanov, E. M.

    2009-01-15

    The problems on the relation of the mean effective molecular polarizability {gamma}-bar to the long-range orientational order of molecules (the optical anisotropy of the medium) in uniaxial and biaxial liquid crystals, the local anisotropy on mesoscopic scales, and the anisotropy of the Lorentz tensor L and the local-field tensor f are formulated and solved. It is demonstrated that the presence of the long-range orientational order of molecules in liquid crystals imposes limitations from below on the molecular polarizability {gamma}-bar, which differs for uniaxial and biaxial liquid crystals. The relation between the local anisotropy and the molecular polarizability {gamma}-bar is investigated for calamitic and discotic uniaxial liquid crystals consisting of lath- and disk-shaped molecules. These liquid crystals with identical macroscopic symmetry differ in the local anisotropy and the relationships between the components L{sub parallel} < L{sub perpendicular} , f{sub parallel} < f{sub perpendicular} (calamitic) and L{sub parallel} > L{sub perpendicular} , f{sub parallel} > f{sub perpendicular} (discotic) for an electric field oriented parallel and perpendicular to the director. The limitations from below and above on the molecular polarizability {gamma}-bar due to the anisotropy of the tensors L and f are established for liquid crystals of both types. These limitations indicate that the molecular polarizability {gamma}-bar depends on the phase state and the temperature. The factors responsible for the nonphysical consequences of the local-field models based on the approximation {gamma}-bar = const are revealed. The theoretical inferences are confirmed by the experimental data for a number of calamitic nematic liquid crystals with different values of birefringence and the discotic liquid crystal Col{sub ho}.

  17. Cooperative Localization for Mobile Networks: A Distributed Belief Propagation–Mean Field Message Passing Algorithm

    NASA Astrophysics Data System (ADS)

    Cakmak, Burak; Urup, Daniel N.; Meyer, Florian; Pedersen, Troels; Fleury, Bernard H.; Hlawatsch, Franz

    2016-06-01

    We propose a hybrid message passing method for distributed cooperative localization and tracking of mobile agents. Belief propagation and mean field message passing are employed for, respectively, the motion-related and measurement-related part of the factor graph. Using a Gaussian belief approximation, only three real values per message passing iteration have to be broadcast to neighboring agents. Despite these very low communication requirements, the estimation accuracy can be comparable to that of particle-based belief propagation.

  18. Electromagnetic vacuum of complex media: Dipole emission versus light propagation, vacuum energy, and local field factors

    SciTech Connect

    Donaire, M.

    2011-02-15

    We offer a unified approach to several phenomena related to the electromagnetic vacuum of a complex medium made of point electric dipoles. To this aim, we apply the linear response theory to the computation of the polarization field propagator and study the spectrum of vacuum fluctuations. The physical distinction among the local density of states which enter the spectra of light propagation, total dipole emission, coherent emission, total vacuum energy, and Schwinger-bulk energy is made clear. Analytical expressions for the spectrum of dipole emission and for the vacuum energy are derived. Their respective relations with the spectrum of external light and with the Schwinger-bulk energy are found. The light spectrum and the Schwinger-bulk energy are determined by the Dyson propagator. The emission spectrum and the total vacuum energy are determined by the polarization propagator. An exact relationship of proportionality between both propagators is found in terms of local field factors. A study of the nature of stimulated emission from a single dipole is carried out. Regarding coherent emission, it contains two components. A direct one which is transferred radiatively and directly from the emitter into the medium and whose spectrum is that of external light. And an indirect one which is radiated by induced dipoles. The induction is mediated by one (and only one) local field factor. Regarding the vacuum energy, we find that in addition to the Schwinger-bulk energy the vacuum energy of an effective medium contains local field contributions proportional to the resonant frequency and to the spectral line width.

  19. Local field potentials in primate motor cortex encode grasp kinetic parameters

    PubMed Central

    Milekovic, Tomislav; Truccolo, Wilson; Grün, Sonja; Riehle, Alexa; Brochier, Thomas

    2015-01-01

    Reach and grasp kinematics are known to be encoded in the spiking activity of neuronal ensembles and in local field potentials (LFPs) recorded from primate motor cortex during movement planning and execution. However, little is known, especially in LFPs, about the encoding of kinetic parameters, such as forces exerted on the object during the same actions. We implanted two monkeys with microelectrode arrays in the motor cortical areas MI and PMd to investigate encoding of grasp-related parameters in motor cortical LFPs during planning and execution of reach-and-grasp movements. We identified three components of the LFP that modulated during grasps corresponding to low (0.3 - 7Hz), intermediate (∼10 - ∼40Hz) and high (∼80 - 250Hz) frequency bands. We show that all three components can be used to classify not only grip types but also object loads during planning and execution of a grasping movement. In addition, we demonstrate that all three components recorded during planning or execution can be used to continuously decode finger pressure forces and hand position related to the grasping movement. Low and high frequency components provide similar classification and decoding accuracies, which were substantially higher than those obtained from the intermediate frequency component. Our results demonstrate that intended reach and grasp kinetic parameters are encoded in multiple LFP bands during both movement planning and execution. These findings also suggest that the LFP is a reliable signal for the control of parameters related to object load and applied pressure forces in brain-machine interfaces. PMID:25869861

  20. Local field potentials in primate motor cortex encode grasp kinetic parameters.

    PubMed

    Milekovic, Tomislav; Truccolo, Wilson; Grün, Sonja; Riehle, Alexa; Brochier, Thomas

    2015-07-01

    Reach and grasp kinematics are known to be encoded in the spiking activity of neuronal ensembles and in local field potentials (LFPs) recorded from primate motor cortex during movement planning and execution. However, little is known, especially in LFPs, about the encoding of kinetic parameters, such as forces exerted on the object during the same actions. We implanted two monkeys with microelectrode arrays in the motor cortical areas MI and PMd to investigate encoding of grasp-related parameters in motor cortical LFPs during planning and execution of reach-and-grasp movements. We identified three components of the LFP that modulated during grasps corresponding to low (0.3-7Hz), intermediate (~10-~40Hz) and high (~80-250Hz) frequency bands. We show that all three components can be used to classify not only grip types but also object loads during planning and execution of a grasping movement. In addition, we demonstrate that all three components recorded during planning or execution can be used to continuously decode finger pressure forces and hand position related to the grasping movement. Low and high frequency components provide similar classification and decoding accuracies, which were substantially higher than those obtained from the intermediate frequency component. Our results demonstrate that intended reach and grasp kinetic parameters are encoded in multiple LFP bands during both movement planning and execution. These findings also suggest that the LFP is a reliable signal for the control of parameters related to object load and applied pressure forces in brain-machine interfaces. PMID:25869861

  1. Subthalamic local field potentials in Parkinson's disease and isolated dystonia: An evaluation of potential biomarkers.

    PubMed

    Wang, Doris D; de Hemptinne, Coralie; Miocinovic, Svjetlana; Qasim, Salman E; Miller, Andrew M; Ostrem, Jill L; Galifianakis, Nicholas B; San Luciano, Marta; Starr, Philip A

    2016-05-01

    Local field potentials (LFP) recorded from the subthalamic nucleus in patients with Parkinson's disease (PD) demonstrate prominent oscillations in the beta (13-30Hz) frequency range, and reduction of beta band spectral power by levodopa and deep brain stimulation (DBS) is correlated with motor symptom improvement. Several features of beta activity have been theorized to be specific biomarkers of the parkinsonian state, though these have rarely been studied in non-parkinsonian conditions. To compare resting state LFP features in PD and isolated dystonia and evaluate disease-specific biomarkers, we recorded subthalamic LFPs from 28 akinetic-rigid PD and 12 isolated dystonia patients during awake DBS implantation. Spectral power and phase-amplitude coupling characteristics were analyzed. In 26/28 PD and 11/12 isolated dystonia patients, the LFP power spectrum had a peak in the beta frequency range, with similar amplitudes between groups. Resting state power did not differ between groups in the theta (5-8Hz), alpha (8-12Hz), beta (13-30Hz), broadband gamma (50-200Hz), or high frequency oscillation (HFO, 250-350Hz) bands. Analysis of phase-amplitude coupling between low frequency phase and HFO amplitude revealed significant interactions in 19/28 PD and 6/12 dystonia recordings without significant differences in maximal coupling or preferred phase. Two features of subthalamic LFPs that have been proposed as specific parkinsonian biomarkers, beta power and coupling of beta phase to HFO amplitude, were also present in isolated dystonia, including focal dystonias. This casts doubt on the utility of these metrics as disease-specific diagnostic biomarkers. PMID:26884091

  2. Computing the Local Field Potential (LFP) from Integrate-and-Fire Network Models.

    PubMed

    Mazzoni, Alberto; Lindén, Henrik; Cuntz, Hermann; Lansner, Anders; Panzeri, Stefano; Einevoll, Gaute T

    2015-12-01

    Leaky integrate-and-fire (LIF) network models are commonly used to study how the spiking dynamics of neural networks changes with stimuli, tasks or dynamic network states. However, neurophysiological studies in vivo often rather measure the mass activity of neuronal microcircuits with the local field potential (LFP). Given that LFPs are generated by spatially separated currents across the neuronal membrane, they cannot be computed directly from quantities defined in models of point-like LIF neurons. Here, we explore the best approximation for predicting the LFP based on standard output from point-neuron LIF networks. To search for this best "LFP proxy", we compared LFP predictions from candidate proxies based on LIF network output (e.g, firing rates, membrane potentials, synaptic currents) with "ground-truth" LFP obtained when the LIF network synaptic input currents were injected into an analogous three-dimensional (3D) network model of multi-compartmental neurons with realistic morphology, spatial distributions of somata and synapses. We found that a specific fixed linear combination of the LIF synaptic currents provided an accurate LFP proxy, accounting for most of the variance of the LFP time course observed in the 3D network for all recording locations. This proxy performed well over a broad set of conditions, including substantial variations of the neuronal morphologies. Our results provide a simple formula for estimating the time course of the LFP from LIF network simulations in cases where a single pyramidal population dominates the LFP generation, and thereby facilitate quantitative comparison between computational models and experimental LFP recordings in vivo. PMID:26657024

  3. Computing the Local Field Potential (LFP) from Integrate-and-Fire Network Models

    PubMed Central

    Cuntz, Hermann; Lansner, Anders; Panzeri, Stefano; Einevoll, Gaute T.

    2015-01-01

    Leaky integrate-and-fire (LIF) network models are commonly used to study how the spiking dynamics of neural networks changes with stimuli, tasks or dynamic network states. However, neurophysiological studies in vivo often rather measure the mass activity of neuronal microcircuits with the local field potential (LFP). Given that LFPs are generated by spatially separated currents across the neuronal membrane, they cannot be computed directly from quantities defined in models of point-like LIF neurons. Here, we explore the best approximation for predicting the LFP based on standard output from point-neuron LIF networks. To search for this best “LFP proxy”, we compared LFP predictions from candidate proxies based on LIF network output (e.g, firing rates, membrane potentials, synaptic currents) with “ground-truth” LFP obtained when the LIF network synaptic input currents were injected into an analogous three-dimensional (3D) network model of multi-compartmental neurons with realistic morphology, spatial distributions of somata and synapses. We found that a specific fixed linear combination of the LIF synaptic currents provided an accurate LFP proxy, accounting for most of the variance of the LFP time course observed in the 3D network for all recording locations. This proxy performed well over a broad set of conditions, including substantial variations of the neuronal morphologies. Our results provide a simple formula for estimating the time course of the LFP from LIF network simulations in cases where a single pyramidal population dominates the LFP generation, and thereby facilitate quantitative comparison between computational models and experimental LFP recordings in vivo. PMID:26657024

  4. Localization and Classification of Paddy Field Pests using a Saliency Map and Deep Convolutional Neural Network.

    PubMed

    Liu, Ziyi; Gao, Junfeng; Yang, Guoguo; Zhang, Huan; He, Yong

    2016-01-01

    We present a pipeline for the visual localization and classification of agricultural pest insects by computing a saliency map and applying deep convolutional neural network (DCNN) learning. First, we used a global contrast region-based approach to compute a saliency map for localizing pest insect objects. Bounding squares containing targets were then extracted, resized to a fixed size, and used to construct a large standard database called Pest ID. This database was then utilized for self-learning of local image features which were, in turn, used for classification by DCNN. DCNN learning optimized the critical parameters, including size, number and convolutional stride of local receptive fields, dropout ratio and the final loss function. To demonstrate the practical utility of using DCNN, we explored different architectures by shrinking depth and width, and found effective sizes that can act as alternatives for practical applications. On the test set of paddy field images, our architectures achieved a mean Accuracy Precision (mAP) of 0.951, a significant improvement over previous methods. PMID:26864172

  5. The Velocity Field of the Local Universe From Measurements of Type Ia Supernovae

    SciTech Connect

    Haugbolle, T.; Hannestad, S.; Thomsen, B.; Fynbo, J.; Sollerman, J.; Jha, S.; /KIPAC, Menlo Park

    2006-12-08

    We present a measurement of the velocity flow of the local universe relative to the CMB rest frame, based on the Jha, Riess & Kirshner (2007) sample of 133 low redshift type Ia supernovae. At a depth of 4500 km s{sup -1} we find a dipole amplitude of 279 {+-} 68 km s{sup -1} in the direction l = 285{sup o} {+-} 18{sup o}, b = -10{sup o} {+-} 15{sup o}, consistent with earlier measurements and with the assumption that the local velocity field is dominated by the Great Attractor region. At a larger depth of 5900 km s{sup -1} we find a shift in the dipole direction towards the Shapley concentration. We also present the first measurement of the quadrupole term in the local velocity flow at these depths. Finally, we have performed detailed studies based on N-body simulations of the expected precision with which the lowest multipoles in the velocity field can be measured out to redshifts of order 0.1. Our mock catalogues are in good agreement with current observations, and demonstrate that our results are robust with respect to assumptions about the influence of local environment on the type Ia supernova rate.

  6. Localization and Classification of Paddy Field Pests using a Saliency Map and Deep Convolutional Neural Network

    PubMed Central

    Liu, Ziyi; Gao, Junfeng; Yang, Guoguo; Zhang, Huan; He, Yong

    2016-01-01

    We present a pipeline for the visual localization and classification of agricultural pest insects by computing a saliency map and applying deep convolutional neural network (DCNN) learning. First, we used a global contrast region-based approach to compute a saliency map for localizing pest insect objects. Bounding squares containing targets were then extracted, resized to a fixed size, and used to construct a large standard database called Pest ID. This database was then utilized for self-learning of local image features which were, in turn, used for classification by DCNN. DCNN learning optimized the critical parameters, including size, number and convolutional stride of local receptive fields, dropout ratio and the final loss function. To demonstrate the practical utility of using DCNN, we explored different architectures by shrinking depth and width, and found effective sizes that can act as alternatives for practical applications. On the test set of paddy field images, our architectures achieved a mean Accuracy Precision (mAP) of 0.951, a significant improvement over previous methods. PMID:26864172

  7. Finite-temperature electron correlations in the framework of a dynamic local-field correction

    SciTech Connect

    Schweng, H.K.; Boehm, H.M. )

    1993-07-15

    The quantum-mechanical version of the Singwi-Tosi-Land-Sjoelander (STLS) approximation is applied to finite temperatures. This approximation has two main advantages. First, it includes a dynamic local-field correction and second, it gives positive values for the pair-distribution function in the short-range region at zero temperature. This is even valid for rather low densities. After a description of the numerical difficulties arising with the use of a dynamic approximation, the results for the static-structure factor and the pair-distribution function are discussed thoroughly. Detailed work is performed on the static part of the local-field correction, with special emphasis put on the investigation of its structure. A peak is found at a wave vector [ital q][approx]2.8 (in units of the Fermi wave vector) for small temperatures, which tends towards higher values of [ital q] with increasing temperature. This peak causes an attractive particle-hole interaction in a certain [ital q] region and thus gives rise to the appearance of a charge-density wave. A parametric description is given for the static local-field correction in order to simplify further applications. Furthermore, the exchange-and-correlation free energy is considered. The results are compared with the STLS results and with the modified convolution approach.

  8. Localization of quantum topology in the presence of matter and gauge fields

    NASA Astrophysics Data System (ADS)

    Atyabi, Farzaneh

    2015-06-01

    In this paper a toy model of quantum topology is reviewed to study effects of matter and gauge fields on the topology fluctuations. In the model a collection of N one-dimensional manifolds is considered where a set of boundary conditions on states of Hilbert space specifies a set of all topologies perceived by quantum particle and probability of having a specific topology is determined by a partition function over all the topologies in the context of noncommutative spectral geometry. In general the topologies will be fuzzy with the exception of a particular case which is localized by imposing a specific boundary condition. Here fermions and bosons are added to the model. It is shown that in the presence of matter, the fuzziness of topology will be dependent on N, however for large N the dependence is removed similar to the case without matter. Also turning on a particular background gauge field can overcome the fuzziness of topology to reach a localized topology with classical interpretation. It can be seen that for large N more opportunities can be provided for choosing the background gauge field to localize the fuzzy topology.

  9. Place Field Repetition and Purely Local Remapping in a Multicompartment Environment

    PubMed Central

    Spiers, Hugo J.; Hayman, Robin M. A.; Jovalekic, Aleksandar; Marozzi, Elizabeth; Jeffery, Kathryn J.

    2015-01-01

    Hippocampal place cells support spatial memory using sensory information from the environment and self-motion information to localize their firing fields. Currently, there is disagreement about whether CA1 place cells can use pure self-motion information to disambiguate different compartments in environments containing multiple visually identical compartments. Some studies report that place cells can disambiguate different compartments, while others report that they do not. Furthermore, while numerous studies have examined remapping, there has been little examination of remapping in different subregions of a single environment. Is remapping purely local or do place fields in neighboring, unaffected, regions detect the change? We recorded place cells as rats foraged across a 4-compartment environment and report 3 new findings. First, we find that, unlike studies in which rats foraged in 2 compartments, place fields showed a high degree of spatial repetition with a slight degree of rate-based discrimination. Second, this repetition does not diminish with extended experience. Third, remapping was found to be purely local for both geometric change and contextual change. Our results reveal the limited capacity of the path integrator to drive pattern separation in hippocampal representations, and suggest that doorways may play a privileged role in segmenting the neural representation of space. PMID:23945240

  10. Do We Need More "Doing" Activities or "Thinking" Activities in the Field Practicum?

    ERIC Educational Resources Information Center

    Lee, Mingun; Fortune, Anne E.

    2013-01-01

    How do MSW students learn new professional skills in the field practicum? Does students' reflection affect the use of other learning activities during the field practicum? Students in field practica participate in activities that involve observation, doing (participatory), and conceptual linkage. In this study of MSW students, conceptual…

  11. RECONSTRUCTING THE INITIAL DENSITY FIELD OF THE LOCAL UNIVERSE: METHODS AND TESTS WITH MOCK CATALOGS

    SciTech Connect

    Wang Huiyuan; Mo, H. J.; Yang Xiaohu; Van den Bosch, Frank C.

    2013-07-20

    Our research objective in this paper is to reconstruct an initial linear density field, which follows the multivariate Gaussian distribution with variances given by the linear power spectrum of the current cold dark matter model and evolves through gravitational instabilities to the present-day density field in the local universe. For this purpose, we develop a Hamiltonian Markov Chain Monte Carlo method to obtain the linear density field from a posterior probability function that consists of two components: a prior of a Gaussian density field with a given linear spectrum and a likelihood term that is given by the current density field. The present-day density field can be reconstructed from galaxy groups using the method developed in Wang et al. Using a realistic mock Sloan Digital Sky Survey DR7, obtained by populating dark matter halos in the Millennium simulation (MS) with galaxies, we show that our method can effectively and accurately recover both the amplitudes and phases of the initial, linear density field. To examine the accuracy of our method, we use N-body simulations to evolve these reconstructed initial conditions to the present day. The resimulated density field thus obtained accurately matches the original density field of the MS in the density range 0.3{approx}<{rho}/ {rho}-bar {approx}<20 without any significant bias. In particular, the Fourier phases of the resimulated density fields are tightly correlated with those of the original simulation down to a scale corresponding to a wavenumber of {approx}1 h Mpc{sup -1}, much smaller than the translinear scale, which corresponds to a wavenumber of {approx}0.15 h Mpc{sup -1}.

  12. Localization microscopy using noncovalent fluorogen activation by genetically encoded fluorogen activating proteins

    PubMed Central

    Maji, Suvrajit; Huang, Fang; Szent-Gyorgyi, Chris; Lidke, Diane S.; Lidke, Keith A.; Bruchez, Marcel P.

    2014-01-01

    The noncovalent equilibrium activation of a fluorogenic malachite green dye and its cognate fluorogen activating protein has been exploited to produce a sparse labeling distribution of densely tagged genetically encoded proteins, enabling single molecule detection and superresolution imaging in fixed and living cells. These sparse labeling conditions are achieved by control of the dye concentration in the milieu, and do not require any photoswitching or photoactivation. The labeling is achieved using physiological buffers and cellular media, and does not require additives or switching buffer to obtain superresolution images. We evaluate superresolution properties and images obtained from a selected fluorogen activating protein clone fused to actin, and show that the photon counts per object fall between those typically reported for fluorescent proteins and switching dye-pairs, resulting in 10-30 nm localization precision per object. This labeling strategy complements existing approaches, and may simplify multicolor labeling of cellular structures. PMID:24194371

  13. Evolution of localized blobs of swirling or buoyant fluid with and without an ambient magnetic field

    SciTech Connect

    Davidson, P. A.; Sreenivasan, Binod; Aspden, A. J.

    2007-02-15

    We investigate the evolution of localized blobs of swirling or buoyant fluid in an infinite, inviscid, electrically conducting fluid. We consider the three cases of a strong imposed magnetic field, a weak imposed magnetic field, and no magnetic field. For a swirling blob in the absence of a magnetic field, we find, in line with others, that the blob bursts radially outward under the action of the centrifugal force, forming a thin annular vortex sheet. A simple model of this process predicts that the vortex sheet thins exponentially fast and that it moves radially outward with constant velocity. These predictions are verified by high-resolution numerical simulations. When an intense magnetic field is applied, this phenomenon is suppressed, with the energy and angular momentum of the blob now diffusing axially along the magnetic field lines, converting the blob into a columnar structure. For modest or weak magnetic fields, there are elements of both types of behavior, with the radial bursting dominating over axial diffusion for weak fields. However, even when the magnetic field is very weak, the flow structure is quite distinct to that of the nonmagnetic case. In particular, a small but finite magnetic field places a lower bound on the thickness of the annular vortex sheet and produces an annulus of counter-rotating fluid that surrounds the vortex core. The behavior of the buoyant blob is similar. In the absence of a magnetic field, it rapidly develops the mushroomlike shape of a thermal, with a thin vortex sheet at the top and sides of the mushroom. Again, a simple model of this process predicts that the vortex sheet at the top of the thermal thins exponentially fast and rises with constant velocity. These predictions are consistent with earlier numerical simulations. Curiously, however, it is shown that the net vertical momentum associated with the blob increases linearly in time, despite the fact that the vertical velocity at the front of the thermal is constant

  14. An authoritative global database for active submarine hydrothermal vent fields

    NASA Astrophysics Data System (ADS)

    Beaulieu, Stace E.; Baker, Edward T.; German, Christopher R.; Maffei, Andrew

    2013-11-01

    The InterRidge Vents Database is available online as the authoritative reference for locations of active submarine hydrothermal vent fields. Here we describe the revision of the database to an open source content management system and conduct a meta-analysis of the global distribution of known active vent fields. The number of known active vent fields has almost doubled in the past decade (521 as of year 2009), with about half visually confirmed and others inferred active from physical and chemical clues. Although previously known mainly from mid-ocean ridges (MORs), active vent fields at MORs now comprise only half of the total known, with about a quarter each now known at volcanic arcs and back-arc spreading centers. Discoveries in arc and back-arc settings resulted in an increase in known vent fields within exclusive economic zones, consequently reducing the proportion known in high seas to one third. The increase in known vent fields reflects a number of factors, including increased national and commercial interests in seafloor hydrothermal deposits as mineral resources. The purpose of the database now extends beyond academic research and education and into marine policy and management, with at least 18% of known vent fields in areas granted or pending applications for mineral prospecting and 8% in marine protected areas.

  15. Computation of localized flow for steady and unsteady vector fields and its applications.

    PubMed

    Wiebel, Alexander; Garth, Christoph; Scheuermann, Gerik

    2007-01-01

    We present, extend, and apply a method to extract the contribution of a subregion of a data set to the global flow. To isolate this contribution, we decompose the flow in the subregion into a potential flow that is induced by the original flow on the boundary and a localized flow. The localized flow is obtained by subtracting the potential flow from the original flow. Since the potential flow is free of both divergence and rotation, the localized flow retains the original features and captures the region-specific flow that contains the local contribution of the considered subdomain to the global flow. In the remainder of the paper, we describe an implementation on unstructured grids in both two and three dimensions for steady and unsteady flow fields. We discuss the application of some widely used feature extraction methods on the localized flow and describe applications like reverse-flow detection using the potential flow. Finally, we show that our algorithm is robust and scalable by applying it to various flow data sets and giving performance figures. PMID:17495325

  16. Universal spin-1/2 fermion field localization on a 5D braneworld

    NASA Astrophysics Data System (ADS)

    Barbosa-Cendejas, Nandinii; Malagón-Morejón, Dagoberto; Mora-Luna, Refugio Rigel

    2015-07-01

    In this work we present a refined method for the localization of spin- fermions on the 5D braneworld paradigm. We begin by proposing a more natural ansatz for the Yukawa coupling in the 5D bulk fermionic action, that guarantees the localization of the ground states for the 4D fermions with right- or left-chirality. In earlier works the existing freedom on the form of the Yukawa coupling was used in a rather speculative way depending on the type of model, the ansatz proposed in this work is suitable for thin and thick braneworld models and can be applied to branes made of a scalar field or not and in this sense it is the more natural choice. Furthermore, we show that the fermion ground states localization allow us to show the absence of tachyonic modes in the left- and right-chiral Kaluza-Klein mass spectrum. More precisely, we show that localization of gravity in the 5D braneworld implies the localization of the spin- fermions.

  17. Local magnetic field measurements and fault creep observations on the San Andreas fault

    USGS Publications Warehouse

    Johnston, M.J.S.; Smith, B.E.; Burford, R.O.

    1980-01-01

    Simultaneous creep and magnetic field records have been obtained for more than 60 episodic creep events since early 1974, no clear magnetic transients or offsets, as suggested by Breiner and Kovach (1968), are observed at or up to several days before the occurrence times of these events. Although some patterns of creep onset times at adjacent stations over periods of weeks to months appear to correspond to some periods of longer term change in local magnetic field, these changes do not always occur and other groups of creep events have no corresponding changes in local magnetic field. Changes in stress related to the surface expression of episodic fault creep on the San Andreas fault can be estimated from dislocation models fit to observations of simultaneous strains and tilts at points near the fault. These stress values are generally less than 1 bar. For these stress levels and with the apparent limited extent of surface failure, tectonomagnetic models of creep events indicate that simultaneous observations of related magnetic field variations at detectable levels of a gamma or so are unlikely. Slip at greater depth may occur more smoothly and would load the near-surface material to failure. These data also argue against large-scale dilatant cracking occurring along the region of the fault presently monitored. ?? 1980.

  18. Focus and enlarge the enhancement region of local electric field by overlapping Ag triangular nanoplates

    NASA Astrophysics Data System (ADS)

    Zhang, Chun-Hong; Zhu, Jian; Li, Jian-Jun; Zhao, Jun-Wu

    2016-01-01

    The local electric field enhancements of overlapping Ag triangular nanoplates are investigated using the discrete dipole approximate (DDA) method. The enhancement region of local electric field in the gap could be focused and enlarged by adjusting the thickness and the number of layers of the nanoplates. For the double-layer Ag triangular nanoplates, with the thickness increasing, the electric field enhancements transform from near the corners to the center of the gap gradually and the intensities get stronger. The largest "hot spot volume" appears as the thickness increases to 20 nm. The plasmonic coupling between the two nanoplates leads to the surface charges accumulating on the surfaces adjoining the gap. The variation of the surface charges due to the increase of the thickness should be responsible for this phenomenon. For the multilayer Ag triangular nanoplates, the enhancement region enlarges as the number of layers increases. And the "hot spot volume" could reach about 72% of the total volume of the middle gap when the number of layers is 6. The large volume of the intense electric field enhancements obtained in overlapping Ag triangular nanoplates provide potential for surface-enhanced Raman scattering (SERS) and surface enhancement fluorescence (SEF) applications. Figures s1-4 are available in electronic form only at http://www.epjap.org

  19. Localized crustal magnetic field inversion using inner- and outer-source altitude vector Slepian functions

    NASA Astrophysics Data System (ADS)

    Plattner, A.; Simons, F. J.

    2015-12-01

    When inverting for a planetary magnetic potential from vector-valued satellite magnetic field data we need to take into account that the recorded data also contain fields not stemming from the planet but from outer sources in space. In classical global spherical-harmonic analysis this is done by fitting, in addition to the inner sources potential field, a linear combination of outer-source spherical harmonics to the data. This approach has been successfully applied to data with global homogeneous coverage and quality but is not suited for purely regional data. In many situations a local method would be beneficial to take full advantage of data with regionally varying quality or coverage, or to avoid ringing artifacts from sharp intensity contrasts. Here we present a local method that allows such a magnetic source separation. We simultaneously create inner-source and outer-source altitude vector Slepian functions by solving an optimization problem that considers the satellite altitude, the upper radial limit of the satellite trajectory, and the maximum spherical-harmonic degree we want to resolve. This new dual-source altitude vector Slepian system allows to invert for both inner-source and outer-source magnetic potential fields from regional data in a computationally efficient manner, as we show with a series of examples for Earth, the Moon, and terrestrial planets.

  20. Hidden local symmetry of Eu{sup 3+} in xenotime-like crystals revealed by high magnetic fields

    SciTech Connect

    Han, Yibo; Ma, Zongwei; Zhang, Junpei; Wang, Junfeng; Du, Guihuan; Xia, Zhengcai; Han, Junbo Li, Liang; Yu, Xuefeng

    2015-02-07

    The excellent optical properties of europium-doped crystals in visible and near infrared wavelength regions enable them to have broad applications in optoelectronics, laser crystals and sensing devices. The local site crystal fields can affect the intensities and peak positions of the photo-emission lines strongly, but they are usually difficult to be clarified due to magnetically degenerate 4f electronic levels coupling with the crystal fields. Here, we provide an effective way to explore the hidden local symmetry of the Eu{sup 3+} sites in different hosts by taking photoluminescence measurements under pulsed high magnetic fields up to 46 T. The zero-field photoluminescence peaks split further at high magnetic fields when the Zeeman splitting energy is comparable to or larger than that of the crystal field induced zero-field splitting. In particular, a magnetic field induced crossover of the local crystal fields has been observed in the GdVO{sub 4}:Eu{sup 3+} crystal, which resulted from the alignment of Gd{sup 3+} magnetic moment in high magnetic fields; and a hexagonally symmetric local crystal fields was observed in the YPO{sub 4} nanocrystals at the Eu{sup 3+} sites characterized by the special axial and rhombic crystal field terms. These distinct Zeeman splitting behaviors uncover the crystal fields-related local symmetry of luminescent Eu{sup 3+} centers in different hosts or magnetic environments, which are significant for their applications in optics and optoelectronics.

  1. The contribution of high frequencies to human brain activity underlying horizontal localization of natural spatial sounds

    PubMed Central

    Leino, Sakari; May, Patrick JC; Alku, Paavo; Liikkanen, Lassi A; Tiitinen, Hannu

    2007-01-01

    Background In the field of auditory neuroscience, much research has focused on the neural processes underlying human sound localization. A recent magnetoencephalography (MEG) study investigated localization-related brain activity by measuring the N1m event-related response originating in the auditory cortex. It was found that the dynamic range of the right-hemispheric N1m response, defined as the mean difference in response magnitude between contralateral and ipsilateral stimulation, reflects cortical activity related to the discrimination of horizontal sound direction. Interestingly, the results also suggested that the presence of realistic spectral information within horizontally located spatial sounds resulted in a larger right-hemispheric N1m dynamic range. Spectral cues being predominant at high frequencies, the present study further investigated the issue by removing frequencies from the spatial stimuli with low-pass filtering. This resulted in a stepwise elimination of direction-specific spectral information. Interaural time and level differences were kept constant. The original, unfiltered stimuli were broadband noise signals presented from five frontal horizontal directions and binaurally recorded for eight human subjects with miniature microphones placed in each subject's ear canals. Stimuli were presented to the subjects during MEG registration and in a behavioral listening experiment. Results The dynamic range of the right-hemispheric N1m amplitude was not significantly affected even when all frequencies above 600 Hz were removed. The dynamic range of the left-hemispheric N1m response was significantly diminished by the removal of frequencies over 7.5 kHz. The subjects' behavioral sound direction discrimination was only affected by the removal of frequencies over 600 Hz. Conclusion In accord with previous psychophysical findings, the current results indicate that frontal horizontal sound localization and related right-hemispheric cortical processes are

  2. Synaptic activation of ribosomal protein S6 phosphorylation occurs locally in activated dendritic domains.

    PubMed

    Pirbhoy, Patricia Salgado; Farris, Shannon; Steward, Oswald

    2016-06-01

    Previous studies have shown that induction of long-term potentiation (LTP) induces phosphorylation of ribosomal protein S6 (rpS6) in postsynaptic neurons, but the functional significance of rpS6 phosphorylation is poorly understood. Here, we show that synaptic stimulation that induces perforant path LTP triggers phosphorylation of rpS6 (p-rpS6) locally near active synapses. Using antibodies specific for phosphorylation at different sites (ser235/236 versus ser240/244), we show that strong synaptic activation led to dramatic increases in immunostaining throughout postsynaptic neurons with selectively higher staining for p-ser235/236 in the activated dendritic lamina. Following LTP induction, phosphorylation at ser235/236 was detectable by 5 min, peaked at 30 min, and was maintained for hours. Phosphorylation at both sites was completely blocked by local infusion of the NMDA receptor antagonist, APV. Despite robust induction of p-rpS6 following high frequency stimulation, assessment of protein synthesis by autoradiography revealed no detectable increases. Exploration of a novel environment led to increases in the number of p-rpS6-positive neurons throughout the forebrain in a pattern reminiscent of immediate early gene induction and many individual neurons that were p-rpS6-positive coexpressed Arc protein. Our results constrain hypotheses about the possible role of rpS6 phosphorylation in regulating postsynaptic protein synthesis during induction of synaptic plasticity. PMID:27194793

  3. Local magnetometry at high fields and low temperatures using InAs Hall sensors

    NASA Astrophysics Data System (ADS)

    Pugel, E.; Shung, E.; Rosenbaum, T. F.; Watkins, S. P.

    1997-10-01

    We characterize the temperature (0.3⩽T⩽300 K), magnetic field (0⩽H⩽80 kOe), and thickness (0.1, 0.5, and 2.5 μm) dependence of the Hall response of high purity InAs epilayers grown using metalorganic chemical vapor deposition. The high sensitivity, linearity, and temperature independence of the response make them attractive for local Hall probe magnetometry, and uniquely qualified for high field applications below liquid helium temperatures. As a stringent test of performance, we use a six element micron-sized array to monitor the internal field gradient during vortex avalanches at milliKelvin temperatures in a single crystal of YBa2Cu3O7-δ.

  4. Tunable Anderson Localization in Hydrogenated Graphene Based on the Electric Field Effect: First-Principles Study

    NASA Astrophysics Data System (ADS)

    Kang, Joongoo; Wei, Su-Huai

    2014-03-01

    We present a mechanism for reversible switching of the Anderson localization (AL) of electrons in hydrogenated graphene through modulation of the H coverage on graphene by external electric fields. The main idea is to exploit the unique acid-base chemistry (i.e., proton transfer reaction) between NH3 gas and hydrogenated graphene, which can be controlled by applying perpendicular electric fields. The proposed field-induced control of disorder in hydrogenated graphene not only has scientific merits in a systematic study of AL of electrons in grapheme but can also lead to new insight into the development of a new type of transistor based on reversible on/off switching of AL. Furthermore, the reversible and effective tuning of the H coverage on graphene should be useful for tailoring material properties of weakly hydrogenated graphene. This work was funded by the NREL LDRD program (DE-AC36-08GO28308).

  5. Local and Global Bifurcations of Flow Fields During Physical Vapor Transport: Application to a Microgravity Experiment

    NASA Technical Reports Server (NTRS)

    Duval, W. M. B.; Singh, N. B.; Glicksman, M. E.

    1996-01-01

    The local bifurcation of the flow field, during physical vapor transport for a parametric range of experimental interest, shows that its dynamical state ranges from steady to aperiodic. Comparison of computationally predicted velocity profiles with laser doppler velocimetry measurements shows reasonable agreement in both magnitude and planform. Correlation of experimentally measured crystal quality with the predicted dynamical state of the flow field shows a degradation of quality with an increase in Rayleigh number. The global bifurcation of the flow field corresponding to low crystal quality indicates the presence of a traveling wave for Ra = 1.09 x 10(exp 5). For this Rayleigh number threshold a chaotic transport state occurs. However, a microgravity environment for this case effectively stabilizes the flow to diffusive-advective and provides the setting to grow crystals with optimal quality.

  6. Local measurements of tearing mode flows and the magnetohydrodynamic dynamo in the Madison Symmetric Torus reversed-field pinch

    SciTech Connect

    Ennis, D. A.; Gangadhara, S.; Den Hartog, D. J.; Ebrahimi, F.; Fiksel, G.; Prager, S. C.; Craig, D.; Anderson, J. K.

    2010-08-15

    The first localized measurements of tearing mode flows in the core of a hot plasma are presented using nonperturbing measurements of the impurity ion flow. Emission from charge exchange recombination is collected by a novel high optical throughput duo spectrometer providing localized ({+-}1 cm) measurements of C{sup +6} impurity ion velocities resolved to <500 m/s with high bandwidth (100 kHz). Poloidal tearing mode flows in the Madison Symmetric Torus reversed-field pinch are observed to be localized to the mode resonant surface with a radial extent much broader than predicted by linear magnetohydrodynamic (MHD) theory but comparable to the magnetic island width. The relative poloidal flow amplitudes among the dominant core modes do not reflect the proportions of the magnetic amplitudes. The largest correlated flows are associated with modes having smaller magnetic amplitudes resonant near the midradius. The MHD dynamo due to these flows on the magnetic axis is measured to be adequate to balance the mean Ohm's law during reduced tearing activity and is significant but does not exclude other dynamo mechanisms from contributing during a surge in reconnection activity.

  7. Expanding Non-solenoidal Startup with Local Helicity Injection to Increased Toroidal Field and Helicity Injection Rate

    NASA Astrophysics Data System (ADS)

    Perry, J. M.; Barr, J. L.; Bodner, G. M.; Bongard, M. W.; Burke, M. G.; Fonck, R. J.; Hinson, E. T.; Lewicki, B. T.; Reusch, J. A.; Schlossberg, D. J.; Winz, G. R.

    2015-11-01

    Local helicity injection (LHI) is a non-solenoidal startup technique under development on the Pegasus ST. Plasma currents up to 0.18 MA have been initiated by LHI in conjunction with poloidal field induction. A 0-D power balance model has been developed to predict plasma current evolution by balancing helicity input against resistive dissipation. The model is being validated against a set of experimental measurements and magnetic reconstructions with radically varied plasma geometric evolutions. Outstanding physics issues with LHI startup are the scalings of confinement and MHD activity with helicity injection rate and toroidal field strength, as well as injector behavior at high field. Preliminary results from the newly-installed Thomson scattering system suggest core temperatures of a few hundred eV during LHI startup. Measurements are being expanded to multiple spatial points for ongoing confinement studies. A set of larger-area injectors is being installed in the lower divertor region, where increased toroidal field will provide a helicity injection rate over 3 times that of outboard injectors. In this regime helicity injection will be the dominant current drive. Experiments with divertor injectors will permit experimental differentiation of several possible confinement models, and demonstrate the feasibility of LHI startup at high field. Work supported by US DOE grant DE-FG02-96ER54375.

  8. Narrow band perfect absorber for maximum localized magnetic and electric field enhancement and sensing applications

    PubMed Central

    Yong, Zhengdong; Zhang, Senlin; Gong, Chensheng; He, Sailing

    2016-01-01

    Plasmonics offer an exciting way to mediate the interaction between light and matter, allowing strong field enhancement and confinement, large absorption and scattering at resonance. However, simultaneous realization of ultra-narrow band perfect absorption and electromagnetic field enhancement is challenging due to the intrinsic high optical losses and radiative damping in metals. Here, we propose an all-metal plasmonic absorber with an absorption bandwidth less than 8 nm and polarization insensitive absorptivity exceeding 99%. Unlike traditional Metal-Dielectric-Metal configurations, we demonstrate that the narrowband perfect absorption and field enhancement are ascribed to the vertical gap plasmonic mode in the deep subwavelength scale, which has a high quality factor of 120 and mode volume of about 10−4 × (λres/n)3. Based on the coupled mode theory, we verify that the diluted field enhancement is proportional to the absorption, and thus perfect absorption is critical to maximum field enhancement. In addition, the proposed perfect absorber can be operated as a refractive index sensor with a sensitivity of 885 nm/RIU and figure of merit as high as 110. It provides a new design strategy for narrow band perfect absorption and local field enhancement, and has potential applications in biosensors, filters and nonlinear optics. PMID:27046540

  9. Narrow band perfect absorber for maximum localized magnetic and electric field enhancement and sensing applications.

    PubMed

    Yong, Zhengdong; Zhang, Senlin; Gong, Chensheng; He, Sailing

    2016-01-01

    Plasmonics offer an exciting way to mediate the interaction between light and matter, allowing strong field enhancement and confinement, large absorption and scattering at resonance. However, simultaneous realization of ultra-narrow band perfect absorption and electromagnetic field enhancement is challenging due to the intrinsic high optical losses and radiative damping in metals. Here, we propose an all-metal plasmonic absorber with an absorption bandwidth less than 8 nm and polarization insensitive absorptivity exceeding 99%. Unlike traditional Metal-Dielectric-Metal configurations, we demonstrate that the narrowband perfect absorption and field enhancement are ascribed to the vertical gap plasmonic mode in the deep subwavelength scale, which has a high quality factor of 120 and mode volume of about 10(-4) × (λres/n)(3). Based on the coupled mode theory, we verify that the diluted field enhancement is proportional to the absorption, and thus perfect absorption is critical to maximum field enhancement. In addition, the proposed perfect absorber can be operated as a refractive index sensor with a sensitivity of 885 nm/RIU and figure of merit as high as 110. It provides a new design strategy for narrow band perfect absorption and local field enhancement, and has potential applications in biosensors, filters and nonlinear optics. PMID:27046540

  10. Narrow band perfect absorber for maximum localized magnetic and electric field enhancement and sensing applications

    NASA Astrophysics Data System (ADS)

    Yong, Zhengdong; Zhang, Senlin; Gong, Chensheng; He, Sailing

    2016-04-01

    Plasmonics offer an exciting way to mediate the interaction between light and matter, allowing strong field enhancement and confinement, large absorption and scattering at resonance. However, simultaneous realization of ultra-narrow band perfect absorption and electromagnetic field enhancement is challenging due to the intrinsic high optical losses and radiative damping in metals. Here, we propose an all-metal plasmonic absorber with an absorption bandwidth less than 8 nm and polarization insensitive absorptivity exceeding 99%. Unlike traditional Metal-Dielectric-Metal configurations, we demonstrate that the narrowband perfect absorption and field enhancement are ascribed to the vertical gap plasmonic mode in the deep subwavelength scale, which has a high quality factor of 120 and mode volume of about 10‑4 × (λres/n)3. Based on the coupled mode theory, we verify that the diluted field enhancement is proportional to the absorption, and thus perfect absorption is critical to maximum field enhancement. In addition, the proposed perfect absorber can be operated as a refractive index sensor with a sensitivity of 885 nm/RIU and figure of merit as high as 110. It provides a new design strategy for narrow band perfect absorption and local field enhancement, and has potential applications in biosensors, filters and nonlinear optics.

  11. Optical properties of surfaces with supercell ab initio calculations: Local-field effects

    NASA Astrophysics Data System (ADS)

    Tancogne-Dejean, Nicolas; Giorgetti, Christine; Véniard, Valérie

    2015-12-01

    Surface optical and electronic properties are crucial for material science and have implications in fields as various as nanotechnology, nonlinear optics, and spectroscopies. In particular, the huge variation of electronic density perpendicular to the surface is expected to play a key role in absorption due to local-field effects. Numerous state-of-the-art theoretical and numerical ab initio formalisms developed for studying these properties are based on supercell approaches, in reciprocal space, due to their efficiency. In this paper, we show that the standard scheme fails for the out-of-plane optical response of the surface. This response is interpreted using the "effective-medium theory" with vacuum and also in terms of interaction between replicas, as the supercell approach implies a periodicity which is absent in the real system. We propose an alternative formulation, also based on the supercell, for computing the macroscopic dielectric function. Application to the clean Si(001) 2 ×1 surface allows us to present the effect of the local fields for both peak positions and line shape on the bulk and surface contributions. It shows how local fields built up for the in-plane and out-of-plane dielectric responses of the surface. In addition to their conceptual impact, our results explain why the standard approach gives reliable predictions for the in-plane components, leading to correct reflectance anisotropy spectra. Our scheme can be further generalized to other low-dimensional geometries, such as clusters or nanowires, and open the way to nonlinear optics for surfaces.

  12. The magnetic field structure in the active solar corona.

    NASA Technical Reports Server (NTRS)

    Schatten, K. H.

    1971-01-01

    The structure of the magnetic field of the active solar corona is discussed with reference to optical and radio observations of the solar atmosphere. Eclipse observations provide evidence of fine scale structures in the solar atmosphere that appear to relate to the coronal magnetic field. The coronal magnetic field used for comparison is calculated from potential theory; the influence of solar activity upon the potential theory field is discussed with reference to observations of the Faraday rotation of a microwave signal from Pioneer 6 as it was occulted by the solar atmosphere. Evidence has been found suggesting the existence of expanding magnetic bottles located at 10 solar radii above flaring active regions. The dynamics of these events is discussed. It is further suggested that these magnetic bottles are an important component in the solar corona.

  13. A Guided Inquiry Activity for Teaching Ligand Field Theory

    ERIC Educational Resources Information Center

    Johnson, Brian J.; Graham, Kate J.

    2015-01-01

    This paper will describe a guided inquiry activity for teaching ligand field theory. Previous research suggests the guided inquiry approach is highly effective for student learning. This activity familiarizes students with the key concepts of molecular orbital theory applied to coordination complexes. Students will learn to identify factors that…

  14. Activated biochar removes 100% dibromochloropropane from field well water

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Activated biochar was produced from almond shells and used in the field to remove dibromochloropropane from a municipal water well. The activated biochar removed 100% of the contaminant for approximately three months and continued to remove it to below treatment standards for an additional three mon...

  15. Field-Scale Modeling of Local Capillary Trapping During CO2 Injection into a Saline Aquifer

    NASA Astrophysics Data System (ADS)

    Ren, B.; Lake, L. W.; Bryant, S. L.

    2015-12-01

    Local capillary trapping is the small-scale (10-2 to 10+1 m) CO2 trapping that is caused by the capillary pressure heterogeneity. The benefit of LCT, applied specially to CO2 sequestration, is that saturation of stored CO2 is larger than the residual gas, yet these CO2 are not susceptible to leakage through failed seals. Thus quantifying the extent of local capillary trapping is valuable in design and risk assessment of geologic storage projects. Modeling local capillary trapping is computationally expensive and may even be intractable using a conventional reservoir simulator. In this paper, we propose a novel method to model local capillary trapping by combining geologic criteria and connectivity analysis. The connectivity analysis originally developed for characterizing well-to-reservoir connectivity is adapted to this problem by means of a newly defined edge weight property between neighboring grid blocks, which accounts for the multiphase flow properties, injection rate, and gravity effect. Then the connectivity is estimated from shortest path algorithm to predict the CO2 migration behavior and plume shape during injection. A geologic criteria algorithm is developed to estimate the potential local capillary traps based only on the entry capillary pressure field. The latter is correlated to a geostatistical realization of permeability field. The extended connectivity analysis shows a good match of CO2 plume computed by the full-physics simulation. We then incorporate it into the geologic algorithm to quantify the amount of LCT structures identified within the entry capillary pressure field that can be filled during CO2 injection. Several simulations are conducted in the reservoirs with different level of heterogeneity (measured by the Dykstra-Parsons coefficient) under various injection scenarios. We find that there exists a threshold Dykstra-Parsons coefficient, below which low injection rate gives rise to more LCT; whereas higher injection rate increases LCT

  16. Nonlinear effects of locally heterogeneous hydraulic conductivity fields on regional stream-aquifer exchanges

    NASA Astrophysics Data System (ADS)

    Zhu, J.; Winter, C. L.; Wang, Z.

    2015-11-01

    Computational experiments are performed to evaluate the effects of locally heterogeneous conductivity fields on regional exchanges of water between stream and aquifer systems in the Middle Heihe River basin (MHRB) of northwestern China. The effects are found to be nonlinear in the sense that simulated discharges from aquifers to streams are systematically lower than discharges produced by a base model parameterized with relatively coarse effective conductivity. A similar, but weaker, effect is observed for stream leakage. The study is organized around three hypotheses: (H1) small-scale spatial variations of conductivity significantly affect regional exchanges of water between streams and aquifers in river basins, (H2) aggregating small-scale heterogeneities into regional effective parameters systematically biases estimates of stream-aquifer exchanges, and (H3) the biases result from slow paths in groundwater flow that emerge due to small-scale heterogeneities. The hypotheses are evaluated by comparing stream-aquifer fluxes produced by the base model to fluxes simulated using realizations of the MHRB characterized by local (grid-scale) heterogeneity. Levels of local heterogeneity are manipulated as control variables by adjusting coefficients of variation. All models are implemented using the MODFLOW (Modular Three-dimensional Finite-difference Groundwater Flow Model) simulation environment, and the PEST (parameter estimation) tool is used to calibrate effective conductivities defined over 16 zones within the MHRB. The effective parameters are also used as expected values to develop lognormally distributed conductivity (K) fields on local grid scales. Stream-aquifer exchanges are simulated with K fields at both scales and then compared. Results show that the effects of small-scale heterogeneities significantly influence exchanges with simulations based on local-scale heterogeneities always producing discharges that are less than those produced by the base model

  17. Nonlinear effects of locally heterogeneous hydraulic conductivity fields on regional stream-aquifer exchanges

    NASA Astrophysics Data System (ADS)

    Zhu, J.; Winter, C. L.; Wang, Z.

    2015-08-01

    Computational experiments are performed to evaluate the effects of locally heterogeneous conductivity fields on regional exchanges of water between stream and aquifer systems in the Middle Heihe River Basin (MHRB) of northwestern China. The effects are found to be nonlinear in the sense that simulated discharges from aquifers to streams are systematically lower than discharges produced by a base model parameterized with relatively coarse effective conductivity. A similar, but weaker, effect is observed for stream leakage. The study is organized around three hypotheses: (H1) small-scale spatial variations of conductivity significantly affect regional exchanges of water between streams and aquifers in river basins, (H2) aggregating small-scale heterogeneities into regional effective parameters systematically biases estimates of stream-aquifer exchanges, and (H3) the biases result from slow-paths in groundwater flow that emerge due to small-scale heterogeneities. The hypotheses are evaluated by comparing stream-aquifer fluxes produced by the base model to fluxes simulated using realizations of the MHRB characterized by local (grid-scale) heterogeneity. Levels of local heterogeneity are manipulated as control variables by adjusting coefficients of variation. All models are implemented using the MODFLOW simulation environment, and the PEST tool is used to calibrate effective conductivities defined over 16 zones within the MHRB. The effective parameters are also used as expected values to develop log-normally distributed conductivity (K) fields on local grid scales. Stream-aquifer exchanges are simulated with K fields at both scales and then compared. Results show that the effects of small-scale heterogeneities significantly influence exchanges with simulations based on local-scale heterogeneities always producing discharges that are less than those produced by the base model. Although aquifer heterogeneities are uncorrelated at local scales, they appear to induce

  18. HIPK2 catalytic activity and subcellular localization are regulated by activation-loop Y354 autophosphorylation.

    PubMed

    Siepi, Francesca; Gatti, Veronica; Camerini, Serena; Crescenzi, Marco; Soddu, Silvia

    2013-06-01

    HIPK2 (homeodomain-interacting protein kinase-2) binds to and phosphorylates, at Ser and Thr residues, a large number of targets involved in cell division and cell fate decision in response to different physiological or stress stimuli. Inactivation of HIPK2 has been observed in human and mouse cancers supporting its role as a tumor suppressor. Despite the biological relevance of this kinase, very little is known on how HIPK2 becomes catalytically active. Based on sequence homologies, HIPK2 has been taxonomically classified as a subfamily member of the dual-specificity tyrosine-regulated kinases (DYRKs) and the activation-loop Y354 of HIPK2 has been found phosphorylated in different cells; however, the relevance of this Y phosphorylation is presently unknown. Here, we show that HIPK2, which is extensively phosphorylated at S/T sites throughout its functional domains, becomes catalytically active by autophosphorylation at the activation-loop Y354. In particular, we found that, in analogy to DYRKs, HIPK2-Y354 phosphorylation is an autocatalytic event and its prevention, through Y354 substitution with non-phosphorylatable amino acids or by using the kinase inhibitor purvalanol A, induces a strong reduction of the HIPK2 S/T-kinase activity on different substrates. Interestingly, at variance from DYRKs, inhibition of HIPK2-Y354 phosphorylation induces a strong out-of-target Y-kinase activity in cis and a strong cytoplasmic relocalization of the kinase. Together, these results demonstrate that the catalytic activity, substrate specificity, and subcellular localization of HIPK2 are regulated by autophosphorylation of its activation-loop Y354. PMID:23485397

  19. HIPK2 catalytic activity and subcellular localization are regulated by activation-loop Y354 autophosphorylation

    PubMed Central

    Siepi, Francesca; Gatti, Veronica; Camerini, Serena; Crescenzi, Marco; Soddu, Silvia

    2013-01-01

    HIPK2 (homeodomain-interacting protein kinase-2) binds to and phosphorylates, at Ser and Thr residues, a large number of targets involved in cell division and cell fate decision in response to different physiological or stress stimuli. Inactivation of HIPK2 has been observed in human and mouse cancers supporting its role as a tumor suppressor. Despite the biological relevance of this kinase, very little is known on how HIPK2 becomes catalytically active. Based on sequence homologies, HIPK2 has been taxonomically classified as a subfamily member of the dual-specificity tyrosine-regulated kinases (DYRKs) and the activation-loop Y354 of HIPK2 has been found phosphorylated in different cells; however, the relevance of this Y phosphorylation is presently unknown. Here, we show that HIPK2, which is extensively phosphorylated at S/T sites throughout its functional domains, becomes catalytically active by autophosphorylation at the activation-loop Y354. In particular, we found that, in analogy to DYRKs, HIPK2-Y354 phosphorylation is an autocatalytic event and its prevention, through Y354 substitution with non-phosphorylatable amino acids or by using the kinase inhibitor purvalanol A, induces a strong reduction of the HIPK2 S/T-kinase activity on different substrates. Interestingly, at variance from DYRKs, inhibition of HIPK2-Y354 phosphorylation induces a strong out-of-target Y-kinase activity in cis and a strong cytoplasmic relocalization of the kinase. Together, these results demonstrate that the catalytic activity, substrate specificity, and subcellular localization of HIPK2 are regulated by autophosphorylation of its activation-loop Y354. PMID:23485397

  20. Ultrasonic Localization of Mobile Robot Using Active Beacons and Code Correlation

    NASA Astrophysics Data System (ADS)

    Peca, Marek

    Ultrasonic localization system for planar mobile robot inside of a restricted field is presented. System is based on stationary active beacons and measurement of distances between beacons and robot, using cross-correlation of pseudorandom binary sequences (PRBSes). Due to high demand of dynamic reserve imposed by range ratio in our specific task, both code- as well as frequency-divided media access has been utilized. For the same reason, 1-bit signal quantization has been abandoned in favor of higher resolution in receiver analog-to-digital conversion. Finally, dynamic estimation of the position is recommended over analytic calculation. The final solution uses the extended Kalman filter (EKF), equipped with erroneous measurement detection, initial state computation, and recovery from being lost. EKF also performs data-fusion with odometry measurement. Unlike the approach in majority of works on mobile robot localization, a model, actuated solely by additive process noise, is presented for the data-fusion. It offers estimation of heading angle, and remains locally observable. Simplistic double integrator model of motion dynamics is described, and the importance of clock dynamics is emphasized.

  1. Nanoscale Imaging of Local Few-Femtosecond Near-Field Dynamics within a Single Plasmonic Nanoantenna

    PubMed Central

    2015-01-01

    The local enhancement of few-cycle laser pulses by plasmonic nanostructures opens up for spatiotemporal control of optical interactions on a nanometer and few-femtosecond scale. However, spatially resolved characterization of few-cycle plasmon dynamics poses a major challenge due to the extreme length and time scales involved. In this Letter, we experimentally demonstrate local variations in the dynamics during the few strongest cycles of plasmon-enhanced fields within individual rice-shaped silver nanoparticles. This was done using 5.5 fs laser pulses in an interferometric time-resolved photoemission electron microscopy setup. The experiments are supported by finite-difference time-domain simulations of similar silver structures. The observed differences in the field dynamics across a single particle do not reflect differences in plasmon resonance frequency or dephasing time. They instead arise from a combination of retardation effects and the coherent superposition between multiple plasmon modes of the particle, inherent to a few-cycle pulse excitation. The ability to detect and predict local variations in the few-femtosecond time evolution of multimode coherent plasmon excitations in rationally synthesized nanoparticles can be used in the tailoring of nanostructures for ultrafast and nonlinear plasmonics. PMID:26375959

  2. Pick and Choose the Spectroscopic Method to Calibrate the Local Electric Field inside Proteins.

    PubMed

    Haldar, Tapas; Kashid, Somnath M; Deb, Pranab; Kesh, Sandeep; Bagchi, Sayan

    2016-07-01

    Electrostatic interactions in proteins play a crucial role in determining the structure-function relation in biomolecules. In recent years, fluorescent probes have been extensively employed to interrogate the polarity in biological cavities through dielectric constants or semiempirical polarity scales. A choice of multiple spectroscopic methods, not limited by fluorophores, along with a molecular level description of electrostatics involving solute-solvent interactions, would allow more flexibility to pick and choose the experimental technique to determine the local electrostatics within protein interiors. In this work we report that ultraviolet/visible-absorption, infrared-absorption, or (13)C NMR can be used to calibrate the local electric field in both hydrogen bonded and non-hydrogen bonded protein environments. The local electric field at the binding site of a serum protein has been determined using the absorption wavelength as well as the carbonyl stretching frequency of its natural steroid substrate, testosterone. Excellent agreement is observed in the results obtained from two independent spectroscopic techniques. PMID:27295386

  3. Manual of Suggested Activities for the Development of Sound Localization Skills.

    ERIC Educational Resources Information Center

    Brothers, Roy J.; Huff, Roger A.

    The manual is intended to provide teachers of young blind children with activities to develop sound localization skills. Both group and individual activities are suggested for the following four categories: activities in which both child and sound are stationary, activities in which the child is stationary but the sound is moving, activities in…

  4. Simultaneous fMRI and local field potential measurements during epileptic seizures in medetomidine sedated rats using RASER pulse sequence

    PubMed Central

    Airaksinen, Antti M; Niskanen, Juha-Pekka; Chamberlain, Ryan; Huttunen, Joanna K; Nissinen, Jari; Garwood, Michael; Pitkänen, Asla; Gröhn, Olli

    2010-01-01

    Simultaneous electrophysiological and functional magnetic resonance imaging (fMRI) measurements of animal models of epilepsy are methodologically challenging, but essential to better understand abnormal brain activity and hemodynamics during seizures. In the present study, fMRI of medetomidine sedated rats was performed using novel Rapid Acquisition by Sequential Excitation and Refocusing (RASER) fast imaging pulse sequence and simultaneous local field potential (LFP) measurements during kainic acid (KA) induced seizures. The image distortion caused by the hippocampal measuring electrode was clearly seen in echo planar imaging (EPI) images, whereas no artifact was seen in RASER images. Robust blood oxygenation level dependent (BOLD) responses were observed in the hippocampus during KA induced seizures. The recurrent epileptic seizures were detected in the LFP signal after KA injection. The presented combination of deep electrode LFP measurements and fMRI under medetomidine anesthesia, that does not significantly suppress KA induced seizures, provides a unique tool for studying abnormal brain activity in rats. PMID:20725933

  5. The gravity of dark vortices: effective field theory for branes and strings carrying localized flux

    NASA Astrophysics Data System (ADS)

    Burgess, C. P.; Diener, R.; Williams, M.

    2015-11-01

    A Nielsen-Olesen vortex usually sits in an environment that expels the flux that is confined to the vortex, so flux is not present both inside and outside. We construct vortices for which this is not true, where the flux carried by the vortex also permeates the `bulk' far from the vortex. The idea is to mix the vortex's internal gauge flux with an external flux using off-diagonal kinetic mixing. Such `dark' vortices could play a phenomenological role in models with both cosmic strings and a dark gauge sector. When coupled to gravity they also provide explicit ultra-violet completions for codimension-two brane-localized flux, which arises in extra-dimensional models when the same flux that stabilizes extra-dimensional size is also localized on space-filling branes situated around the extra dimensions. We derive simple formulae for observables such as defect angle, tension, localized flux and on-vortex curvature when coupled to gravity, and show how all of these are insensitive to much of the microscopic details of the solutions, and are instead largely dictated by low-energy quantities. We derive the required effective description in terms of a world-sheet brane action, and derive the matching conditions for its couplings. We consider the case where the dimensions transverse to the bulk compactify, and determine how the on- and off-vortex curvatures and other bulk features depend on the vortex properties. We find that the brane-localized flux does not gravitate, but just renormalizes the tension in a magnetic-field independent way. The existence of an explicit UV completion puts the effective description of these models on a more precise footing, verifying that brane-localized flux can be consistent with sensible UV physics and resolving some apparent paradoxes that can arise with a naive (but commonly used) delta-function treatment of the brane's localization within the bulk.

  6. Independent and joint effects of personality on intentions to become an active participant in local union activities in Canada.

    PubMed

    McPhee, Deborah M; Sears, Greg J; Wiesner, Willi H

    2014-01-01

    Drawing on the theory of planned behavior (TPB), this field study (N = 282) investigates the impact of two focal personality traits, extraversion and conscientiousness, on employees' attitudes and intentions to actively participate in their local union. Consistent with the TPB, subjective norms, perceived behavioral control, and attitudes toward participation each explained unique variance in union participation intentions. Furthermore, results revealed that extraversion was positively related, and conscientiousness was negatively related to participation intentions, with attitudes toward participation mediating these effects. A significant interaction between extraversion and conscientiousness was also observed, such that introverted workers higher in conscientiousness were less inclined to express positive attitudes toward union participation. Overall, these results provide support for the utility of the TPB in predicting union participation intentions and highlight the vital role that personality traits may play in determining union participation attitudes and intentions. PMID:24684076

  7. Large plasmaspheric electric fields at L approximately 2 measured by the S3-3 satellite during strong geomagnetic activity

    NASA Technical Reports Server (NTRS)

    Gonzalez, W. D.; Pinto, O., Jr.; Mendes, O., Jr.; Mozer, F. S.

    1986-01-01

    Large plasmaspheric electric fields at L is approximately 2 measured by the S3-3 satellite during strong geomagnetic activity are reported. Since these measurements have amplitudes comparable to those of the local corotation electric field, during such events the plasmasphere is expected to get strongly altered event at such low L-values. Furthermore, those measurements could contribute to the understanding of the physics of the convection/electric field penetration to the low latitude plasmaphere as well as the disturbed dynamo, during strong geomagnetic activity. For this purpose, critical parameters related to geomagnetic activity are also presented for the reported electric field events.

  8. The Contribution of Local Stresses in the Western Europe Stress Field

    NASA Astrophysics Data System (ADS)

    Kusters, D.; Camelbeeck, T.; de Viron, O.; Van Camp, M. J.

    2013-12-01

    The analysis of the World Stress Map (WSM) has evidenced first and second stress patterns (Heidbach et al. 2013) in Western Europe. The long wavelength pattern is controlled by plate boundary forces and transmitted into the plate interior. The second order is due to local topography, density and strength contrasts and can modify significantly the long wavelength component of the stress field. We propose to use the second spatial derivatives of a geoid height grid to evaluate the stress generated at the local scale by the spatial variations of the Gravitational Potential Energy (GPE), which is related to inhomogeneous topography and mass distribution in the lithosphere (Camelbeeck et al., 2013). This allows estimating whether this local component could be dominant in the tectonic stress, mainly by comparing our results with the WSM dataset and earthquake fault-plane solutions. For the northern Alps, we obtain results similar to the ones obtained for the Pyrenees by Camelbeeck et al. (Lithosphere, 2013), i.e. 70% of focal mechanisms are in agreement with the local stresses inferred from the geoid. This agrees with Heidbach et al. (2007), who showed that the short wavelength stress pattern is predominant in the Alps In Great Britain, the first order pattern is expected to be the main factor in the global stress field such that in principle, our method may not be appropriate. However, our tectonic style predicted from the geoid agrees with most of the earthquake focal mechanisms, of which 70% correspond to our main horizontal stress direction (σH). Hence, the local stresses should not be neglected when assessing the overall stress state in the UK. On the South Norway shelf, Pascal and Cloetingh (2009) computed the gravitational potential stresses (GPSt). This model generally reflects the WSM and has an intermediate wavelength pattern. However, it does not allow estimating the local stresses due to small geological structures. At such short wavelength, our method

  9. Distribution of the Height of Local Maxima of Gaussian Random Fields*

    PubMed Central

    Cheng, Dan; Schwartzman, Armin

    2015-01-01

    Let {f(t) : t ∈ T} be a smooth Gaussian random field over a parameter space T, where T may be a subset of Euclidean space or, more generally, a Riemannian manifold. We provide a general formula for the distribution of the height of a local maximum P{f(t0)>u∣t0 is a local maximum of f(t)} when f is non-stationary. Moreover, we establish asymptotic approximations for the overshoot distribution of a local maximum P{f(t0)>u+v∣t0 is a local maximum of f(t) and f(t0) > v} as v → ∞. Assuming further that f is isotropic, we apply techniques from random matrix theory related to the Gaussian orthogonal ensemble to compute such conditional probabilities explicitly when T is Euclidean or a sphere of arbitrary dimension. Such calculations are motivated by the statistical problem of detecting peaks in the presence of smooth Gaussian noise. PMID:26478714

  10. Seasonal prediction of lightning activity in North Western Venezuela: Large-scale versus local drivers

    NASA Astrophysics Data System (ADS)

    Muñoz, Á. G.; Díaz-Lobatón, J.; Chourio, X.; Stock, M. J.

    2016-05-01

    The Lake Maracaibo Basin in North Western Venezuela has the highest annual lightning rate of any place in the world (~ 200 fl km- 2 yr- 1), whose electrical discharges occasionally impact human and animal lives (e.g., cattle) and frequently affect economic activities like oil and natural gas exploitation. Lightning activity is so common in this region that it has a proper name: Catatumbo Lightning (plural). Although short-term lightning forecasts are now common in different parts of the world, to the best of the authors' knowledge, seasonal prediction of lightning activity is still non-existent. This research discusses the relative role of both large-scale and local climate drivers as modulators of lightning activity in the region, and presents a formal predictability study at seasonal scale. Analysis of the Catatumbo Lightning Regional Mode, defined in terms of the second Empirical Orthogonal Function of monthly Lightning Imaging Sensor (LIS-TRMM) and Optical Transient Detector (OTD) satellite data for North Western South America, permits the identification of potential predictors at seasonal scale via a Canonical Correlation Analysis. Lightning activity in North Western Venezuela responds to well defined sea-surface temperature patterns (e.g., El Niño-Southern Oscillation, Atlantic Meridional Mode) and changes in the low-level meridional wind field that are associated with the Inter-Tropical Convergence Zone migrations, the Caribbean Low Level Jet and tropical cyclone activity, but it is also linked to local drivers like convection triggered by the topographic configuration and the effect of the Maracaibo Basin Nocturnal Low Level Jet. The analysis indicates that at seasonal scale the relative contribution of the large-scale drivers is more important than the local (basin-wide) ones, due to the synoptic control imposed by the former. Furthermore, meridional CAPE transport at 925 mb is identified as the best potential predictor for lightning activity in the Lake

  11. Scalar field localization on 3-branes placed at a warped resolved conifold

    SciTech Connect

    Silva, J. E. G.; Almeida, C. A. S.

    2011-10-15

    We have studied the localization of a scalar field on a 3-brane embedded in a six-dimensional warped bulk of the form M{sub 4}xC{sub 2}, where M{sub 4} is a 3-brane and C{sub 2} is a 2-cycle of a six-dimensional resolved conifold C{sub 6} over a T{sup 1,1} space. Since the resolved conifold is singularity-free in r=0 depending on a resolution parameter a, we have analyzed the behavior of the localization of a scalar field when we vary the resolution parameter. On one hand, this enables us to study the effects that a singularity has on the field. On the other hand we can use the resolution parameter as a fine-tuning between the bulk Planck mass and 3-brane Planck mass and so it opens a new perspective to extend the hierarchy problem. Using a linear and a nonlinear warp factor, we have found that the massive and massless modes are trapped to the brane even in the singular cone (a{ne}0). We have also compared the results obtained in this geometry and those obtained in other six-dimensional models, such as stringlike geometry and cigarlike universe geometry.

  12. Locality and Word Order in Active Dependency Formation in Bangla

    PubMed Central

    Chacón, Dustin A.; Imtiaz, Mashrur; Dasgupta, Shirsho; Murshed, Sikder M.; Dan, Mina; Phillips, Colin

    2016-01-01

    Research on filler-gap dependencies has revealed that there are constraints on possible gap sites, and that real-time sentence processing is sensitive to these constraints. This work has shown that comprehenders have preferences for potential gap sites, and immediately detect when these preferences are not met. However, neither the mechanisms that select preferred gap sites nor the mechanisms used to detect whether these preferences are met are well-understood. In this paper, we report on three experiments in Bangla, a language in which gaps may occur in either a pre-verbal embedded clause or a post-verbal embedded clause. This word order variation allows us to manipulate whether the first gap linearly available is contained in the same clause as the filler, which allows us to dissociate structural locality from linear locality. In Experiment 1, an untimed ambiguity resolution task, we found a global bias to resolve a filler-gap dependency with the first gap linearly available, regardless of structural hierarchy. In Experiments 2 and 3, which use the filled-gap paradigm, we found sensitivity to disruption only when the blocked gap site is both structurally and linearly local, i.e., the filler and the gap site are contained in the same clause. This suggests that comprehenders may not show sensitivity to the disruption of all preferred gap resolutions. PMID:27610090

  13. Locality and Word Order in Active Dependency Formation in Bangla.

    PubMed

    Chacón, Dustin A; Imtiaz, Mashrur; Dasgupta, Shirsho; Murshed, Sikder M; Dan, Mina; Phillips, Colin

    2016-01-01

    Research on filler-gap dependencies has revealed that there are constraints on possible gap sites, and that real-time sentence processing is sensitive to these constraints. This work has shown that comprehenders have preferences for potential gap sites, and immediately detect when these preferences are not met. However, neither the mechanisms that select preferred gap sites nor the mechanisms used to detect whether these preferences are met are well-understood. In this paper, we report on three experiments in Bangla, a language in which gaps may occur in either a pre-verbal embedded clause or a post-verbal embedded clause. This word order variation allows us to manipulate whether the first gap linearly available is contained in the same clause as the filler, which allows us to dissociate structural locality from linear locality. In Experiment 1, an untimed ambiguity resolution task, we found a global bias to resolve a filler-gap dependency with the first gap linearly available, regardless of structural hierarchy. In Experiments 2 and 3, which use the filled-gap paradigm, we found sensitivity to disruption only when the blocked gap site is both structurally and linearly local, i.e., the filler and the gap site are contained in the same clause. This suggests that comprehenders may not show sensitivity to the disruption of all preferred gap resolutions. PMID:27610090

  14. Localization and mass spectrum of q-form fields on branes

    NASA Astrophysics Data System (ADS)

    Fu, Chun-E.; Zhong, Yuan; Xie, Qun-Ying; Liu, Yu-Xiao

    2016-06-01

    In this paper, we investigate localization of a bulk massless q-form field on codimension-one branes by using a new Kaluza-Klein (KK) decomposition, for which there are two types of KK modes for the bulk q-form field, the q-form and (q - 1)-form modes. The first modes may be massive or massless while the second ones are all massless. These two types of KK modes satisfy two Schrödinger-like equations. For a five-dimensional brane model with a finite extra dimension, the spectrum of a bulk 3-form field on the brane consists of some massive bound 3-form KK modes as well as some massless bound 2-form ones with different configuration along the extra dimension. These 2-form modes are different from those obtained from a bulk 2-form field. For a five-dimensional degenerated Bloch brane model with an infinite extra dimension, some massive 3-form resonant KK modes and corresponding massless 2-form resonant ones are obtained for a bulk 3-form field.

  15. Uncertain Acoustic Field Modeling and Robust Source Localization in Shallow Water

    NASA Astrophysics Data System (ADS)

    Zhao, Hangfang; Gong, Xianyi; Yu, Zibin

    2010-09-01

    Oceanic environmental uncertainty can cause significant performance degradation of the SONAR system. Understanding and modeling the uncertainty propagating from environment to acoustic field and then to steering vector is necessary for SONAR design and operation to mitigate the uncertainty effect and provide robust detection and location of targets. The statistical property of uncertainty can be described by the probability density functions or second-order moments of environmental parameters and acoustic fields. Based on the probability description, a stochastic response surface method is used to propagate the uncertainty from environment to acoustic field by polynomial chaos expansion. Then covariance matrix and associated ellipsoidal neighboring space are used to describe the uncertainty set of acoustic field and steering vector for sonar signal processing. Finally, a robust Minimum Variance (MV) matched-field processing method is derived by extending the constrained optimization of MV from single point to an uncertainty steering vector ellipsoid. We apply sea test data collected by a vertical array in shallow water to source localization.

  16. Nucleation of 360 deg DWs in a wire using a local circular field

    NASA Astrophysics Data System (ADS)

    Kaya, Fikriye Idil; Sarella, Anandakumar; Aidala, Katherine E.

    2015-03-01

    Understanding domain wall (DW) motion in ferromagnetic nanostructures is important to realize proposed magnetic data storage and logic devices. Interest in 360o DWs has increased recently with the recognition that their minimal stray field creates only short range interactions, leading to a potentially higher packing density compared to 180o DWs. Our simulations demonstrate the feasibility of nucleating a 360o DW at a specific location along a wire by applying a local circular field that is centered in close proximity to the wire. We simulate the field strength as if from a current carrying wire, which can be experimentally realized by passing current through the tip of an AFM [ 1 , 2 ]. The successful nucleation of a 360o DW depends on the dimensions of the Py wire, on the strength of the circular field, and on the distance of the center of the field from the wire. Once a 360o DW is nucleated, its position shifts with time. We use a notch to stabilize the location of the 360o DW. We investigate the optimal size and spacing of the notches to allow the greatest packing density with control over the nucleation and annihilation of individual domain walls. Supported by NSF DMR-1207924.

  17. Simulation of Multi-Spacecraft Observed Energetic Electron Injection By the Electromagnetic Field of a Transient, Localized Dipolarizing Flux Bundle

    NASA Astrophysics Data System (ADS)

    Gabrielse, C.; Angelopoulos, V.; Runov, A.; Turner, D. L.

    2014-12-01

    Energetic particle injections in the near-Earth plasma sheet are critical for supplying particles and energy to the radiation belts and ring current. Their origin, however, has been elusive due to the lack of equatorial, multi-point observations. After the launch of NASA's Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission in 2007, intense electric fields and elevated energetic particle fluxes have been observed to accompany localized (1-4 RE wide) bursty bulk flows and to propagate from the mid-tail regions (at geocentric radial distances R > 25RE) towards Earth, up to and at times inside of geosynchronous orbit (GEO, R=6.6RE). Motivated by these observations, we model simultaneous multi-point observations of electron injections using guiding center approximation in prescribed but realistic electric and magnetic fields to better understand the nature of their acceleration. Modeling of electron injections assuming a localized, impulsive, dipolarizing flux bundle and its accompanying electric field transported from mid-tail to near-Earth at bursty flow speeds successfully reproduces the observations at multiple spacecraft. The impulsive, localized nature of the earthward-propagating electromagnetic pulse with attending vortical/tailward flow is what makes this model particularly effective in reproducing both the injection and the dispersed decrease in energy flux often observed simultaneously with the injection but at lower energies (~10-30 keV). The results suggest that particle acceleration and transport towards the inner magnetosphere can be thought of as a superposition of individual bursts of varying intensity and cadence depending on global geomagnetic activity levels.

  18. Distinctive response of many-body localized systems to a strong electric field

    NASA Astrophysics Data System (ADS)

    Kozarzewski, Maciej; Prelovšek, Peter; Mierzejewski, Marcin

    2016-06-01

    We study systems that are close to or within the many-body localized (MBL) regime and are driven by a strong electric field. In the ergodic regime, the disorder extends the applicability of the equilibrium linear-response theory to stronger drivings, whereas the response of the MBL systems is very distinctive, revealing currents with damped oscillations. The oscillation frequency is independent of driving and the damping is not due to heating but rather due to dephasing. The details of damping depend on the system's history reflecting the nonergodicity of the MBL phase, while the frequency of the oscillations remains a robust hallmark of localization. Our results suggest that another distinctive characteristic of the driven MBL phase is also a logarithmic increase of the energy and the polarization with time.

  19. Thinking Globally and Acting Locally: Environmental Education Teaching Activities.

    ERIC Educational Resources Information Center

    Mann, Lori D.; Stapp, William B.

    Provided are teaching activities related to: (1) food production and distribution; (2) energy; (3) transportation; (4) solid waste; (5) chemicals in the environment; (6) resource management; (7) pollution; (8) population; (9) world linkages; (10) endangered species; and (11) lifestyle and environment. The activities, designed to help learners…

  20. Finding the Shadows: Local Variations in the Stress Field due to Large Magnitude Earthquakes

    NASA Astrophysics Data System (ADS)

    Latimer, C.; Tiampo, K.; Rundle, J.

    2009-05-01

    Stress shadows, regions of static stress decrease associated with large magnitude earthquake have typically been described through several characteristics or parameters such as location, duration, and size. These features can provide information about the physics of the earthquake itself, as static stress changes are dependent on the following parameters: the regional stress orientations, the coefficient of friction, as well as the depth of interest (King et al, 1994). Areas of stress decrease, associated with a decrease in the seismicity rate, while potentially stable in nature, have been difficult to identify in regions of high rates of background seismicity (Felzer and Brodsky, 2005; Hardebeck et al., 1998). In order to obtain information about these stress shadows, we can determine their characteristics by using the Pattern Informatics (PI) method (Tiampo et al., 2002; Tiampo et al., 2006). The PI method is an objective measure of seismicity rate changes that can be used to locate areas of increases and/or decreases relative to the regional background rate. The latter defines the stress shadows for the earthquake of interest, as seismicity rate changes and stress changes are related (Dieterich et al., 1992; Tiampo et al., 2006). Using the data from the PI method, we can invert for the parameters of the modeled half-space using a genetic algorithm inversion technique. Stress changes will be calculated using coulomb stress change theory (King et al., 1994) and the Coulomb 3 program is used as the forward model (Lin and Stein, 2004; Toda et al., 2005). Changes in the regional stress orientation (using PI results from before and after the earthquake) are of the greatest interest as it is the main factor controlling the pattern of the coulomb stress changes resulting from any given earthquake. Changes in the orientation can lead to conclusions about the local stress field around the earthquake and fault. The depth of interest and the coefficient of friction both

  1. Local school policies increase physical activity in Norwegian secondary schools

    PubMed Central

    Haug, Ellen; Torsheim, Torbjørn; Samdal, Oddrun

    2010-01-01

    SUMMARY The implementation of school policies to support the adoption of physical activity is one of the main strategies recommended to increase physical activity levels among this age group. However, documentation of the effect of such policies is so far limited. The purpose of this study was to explore policy-related practices to support physical activity in Norwegian secondary schools and their association with recess physical activity. Emphasis was given to examine the association between policies and physical activity, over and beyond, individual level interests and environmental factors and to examine cross-level interaction effects. This cross-sectional study was based on a nationally representative sample of Norwegian secondary schools and grade 8 students who participated in the Health Behaviour in School-aged Children (HBSC) 2005/06 study. The final sample comprised 68 schools and 1347 students. Data were collected through questionnaires. The results showed that schools with a written policy for physical activity and schools offering organized non-curricular physical activity several times a week had a higher proportion of students reporting daily participation in recess physical activity. Multilevel logistic regression analysis demonstrated a cross-level main effect of the policy index after controlling for sex, socio-economic status, individual-level interests and the physical environment. A significant contribution of adding the policy index to the prediction of recess physical activity above that provided by the individual-level interests and the physical environment was demonstrated. The results are encouraging and give scientific support to policy documents recommending the implementation of school policies to increase physical activity. PMID:19884244

  2. Local determination of ionospheric electric fields from coherent scatter radar data using the SECS technique

    NASA Astrophysics Data System (ADS)

    Amm, O.; Grocott, A.; Lester, M.; Yeoman, T.

    2009-04-01

    Due to the variable spatio-temporal availability of backscatter from ionospheric coherent scatter radars like SuperDARN or STARE, merging the line-of-sight data of ionospheric plasma velocities that are measured by the radars to spatial maps of such velocities or of electric fields is a non-trivial task. Often this task is solved in a way that statistical a priori information about the global ionospheric electric potential is used in addition to the actual measured data, in order to compensate for lack of measurements in certain regions. However, the disadvantage of such a solution is that the influence of the a priori model may get strong or even dominating the results, in which cases it is hard to determine how well the resulting electric field represents the actual situation for a given point of time and space. Spherical elementary currents systems (SECS) are basis functions that can describe any continuously differentiable vector field on a sphere. Originally, they have successfully been applied to model ionospheric currents based on ground and spacecraft magnetic field data, which explains the historical notion of "current systems" in the name. We present a new technique based on SECS that allows to model distributions of ionospheric plasma flows or electric fields based on coherent scatter radar data of line-of-sight plasma flows without any additional statistical a priori assumptions, on a local region within which the backscatter availability was moderate to good. This region can have any shape and does not need to have boundaries along constant latitude or longitude. Using a synthetic electric field model and variable backscatter availability levels to create input data sets, we test how well the technique is able to reconstruct the original electric field, as a function of available backscatter. Finally, the application of the technique is demonstrated for real data cases, measured by the CUTLASS radars over northern Europe.

  3. The Animal Exhibits at the Field Museum. Activities for Focused Field Trips.

    ERIC Educational Resources Information Center

    Wickland, Thomas, J.

    Museum visits allow students to see animals from South America, North America, Africa, Asia, and the North Pole without rain, snow, or mosquitoes. This activity guide was developed for teachers, chaperones, and students to use with the animal exhibits in the Daniel F. and Ada L. Rice Wing of the Field Museum of Chicago. Activities are designed for…

  4. Local-field corrections to surface and interface core-level shifts in insulators

    SciTech Connect

    Rotenberg, E. ); Olmstead, M.A. )

    1992-11-15

    We present a model for the extra-atomic contributions to core-level shifts in insulating thin films on polarizable substrates. The final-state shift is calculated from the screening-dependent local fields at a photoemitting atom and shown to be comparable to the initial-state Madelung potential shift in polar crystals. For Xe(111) films, our model completely accounts for experimental results. For NaCl(100) and CaF{sub 2}(111) surfaces, we present predictions of surface core-level shifts for simple bulk terminations. We discuss corrections which can be incorporated into our model.

  5. Locally covariant quantum field theory and the spin-statistics connection

    NASA Astrophysics Data System (ADS)

    Fewster, Christopher J.

    2016-03-01

    The framework of locally covariant quantum field theory (QFT), an axiomatic approach to QFT in curved spacetime (CST), is reviewed. As a specific focus, the connection between spin and statistics is examined in this context. A new approach is given, which allows for a more operational description of theories with spin and for the derivation of a more general version of the spin-statistics connection in CSTs than previously available. This part of the text is based on [C. J. Fewster, arXiv:1503.05797.] and a forthcoming publication; the emphasis here is on the fundamental ideas and motivation.

  6. Enhancement of Optical Nonlinearities in Composite Media and Structures via Local Fields and Electromagnetic Coupling Effects

    NASA Technical Reports Server (NTRS)

    Smith, David D.

    2002-01-01

    This talk will review the linear and nonlinear optical properties of metal nanoparticles and dielectric microparticles, with an emphasis on local field effects, and whispering gallery modes (WGMs), as well as the conjunction of these two effects for enhanced Raman. In particular, enhanced optical properties that result from electromagnetic coupling effects will be discussed in the context of Mie scattering from concentric spheres and bispheres. Predictions of mode splitting and photonic bandgaps in micro-spheres will be presented and will be shown to be analogous to effects that occur in coupled resonator optical waveguides (CROW). Slow and fast light in SCISSOR / CROW configurations will also be discussed.

  7. Isotropic proton-detected local-field nuclear magnetic resonancein solids

    SciTech Connect

    Havlin, Robert H.; Walls, Jamie D.; Pines, Alexander

    2004-08-04

    A new nuclear magnetic resonance (NMR) method is presented which produces linear, isotropic proton-detected local-field spectra for InS spin systems in powdered samples. The method, HETeronuclear Isotropic Evolution (HETIE), refocuses the anisotropic portion of the heteronuclear dipolar coupling frequencies by evolving the system under a series of specially designed Hamiltonians and evolution pathways. The theory behind HETIE is represented along with experimental studies conducted on a powdered sample of ferrocene, demonstrating the methodology outlined in this paper. Applications of HETIE for structural determination in solid-state NMR are discussed.

  8. Electric field induced localization phenomena in a ladder network with superlattice configuration: Effect of backbone environment

    NASA Astrophysics Data System (ADS)

    Dutta, Paramita; Maiti, Santanu K.; Karmakar, S. N.

    2014-09-01

    Electric field induced localization properties of a tight-binding ladder network in presence of backbone sites are investigated. Based on Green's function formalism we numerically calculate two-terminal transport together with density of states for different arrangements of atomic sites in the ladder and its backbone. Our results lead to a possibility of getting multiple mobility edges which essentially plays a switching action between a completely opaque to fully or partly conducting region upon the variation of system Fermi energy, and thus, support in fabricating mesoscopic or DNA-based switching devices.

  9. Submicron sensors of local electric field with single-electron resolution at room temperature

    NASA Astrophysics Data System (ADS)

    Barbolina, I. I.; Novoselov, K. S.; Morozov, S. V.; Dubonos, S. V.; Missous, M.; Volkov, A. O.; Christian, D. A.; Grigorieva, I. V.; Geim, A. K.

    2006-01-01

    We describe probes of a local electric field, which are capable of detecting an electric charge as small as the charge of one electron e, operational under ambient conditions and having a spatial resolution down to 100nm. The submicron-sized probes were made from a high-density high-mobility two-dimensional electron gas, which is sensitive to the presence of electric charges near its surface. We demonstrate the possibility of using such microprobes for life-science applications by measuring an electric response of individual yeast cells to abrupt changes in their environment.

  10. Media processing with field-programmable gate arrays on a microprocessor's local bus

    NASA Astrophysics Data System (ADS)

    Bove, V. Michael, Jr.; Lee, Mark; Liu, Yuan-Min; McEniry, Christopher; Nwodoh, Thomas A.; Watlington, John A.

    1998-12-01

    The Chidi system is a PCI-bus media processor card which performs its processing tasks on a large field-programmable gate array (Altera 10K100) in conjunction with a general purpose CPU (PowerPC 604e). Special address-generation and buffering logic (also implemented on FPGAs) allows the reconfigurable processor to share a local bus with the CPU, turning burst accesses to memory into continuous streams and converting between the memory's 64-bit words and the media data types. In this paper we present the design requirements for the Chidi system, describe the hardware architecture, and discuss the software model for its use in media processing.

  11. High flare activity and redistribution of solar global magnetic fields

    NASA Astrophysics Data System (ADS)

    Bumba, V.; Hejna, L.; Gesztelyi, L.

    It is demonstrated that, both on the global scale and on the scale of large and complex active regions, high flare activity is closely related to changes in the whole background magnetic-field distribution. It is found that the disturbances of the normal course of magnetic active longitudes (MAL) during the years 1965-1980 correlated with the maxima of flare activity, while the mode of the MAL distribution correlated with the mean level of solar flare numbers. The development of activity during the last two submaxima of the 21st cycle, especially the formation of the white-light flare region of April 1984, were parts of global processes in the solar atmosphere. They were accompanied by a complete reorganization of the MAL patterns, background field sector structure, and coronal holes.

  12. Program activities, DOE state and local assistance programs, 1980 report

    SciTech Connect

    Chiogioji, Melvin H.

    1981-01-01

    Progress achieved by DOE State and Local Assistance Programs during FY 1980 and since they were established is summarized. These programs enable improved energy efficiency of industry, transportation, commercial establishments, public buildings, and residences. Eight programs (State Energy Conservation, Energy Extension Service, Weatherization Assistance, Institutional Buildings Grants, Energy-Related Inventions, Appropriate Technology Small Grants, Emergency Energy Conservation, Emergency Building Temperature Restrictions) are described. They provide the impetus for thousands of individual and organizational actions that have significantly affected national energy use patterns. (MCW)

  13. Ultra-fast magnetic vortex core reversal by a local field pulse

    SciTech Connect

    Rückriem, R.; Albrecht, M.; Schrefl, T.

    2014-02-03

    Magnetic vortex core reversal of a 20-nm-thick permalloy disk with a diameter of 100 nm was studied by micromagnetic simulations. By applying a global out-of-plane magnetic field pulse, it turned out that the final core polarity is very sensitive to pulse width and amplitude, which makes it hard to control. The reason for this phenomenon is the excitation of radial spin waves, which dominate the reversal process. The excitation of spin waves can be strongly suppressed by applying a local field pulse within a small area at the core center. With this approach, ultra-short reversal times of about 15 ps were achieved, which are ten times faster compared to a global pulse.

  14. FIBER BRAGG GRATING SENSORS FOR LOCALIZED STRAIN MEASUREMENTS AT LOW TEMPERATURE AND IN HIGH MAGNETIC FIELD

    SciTech Connect

    Ramalingam, Rajinikumar

    2010-04-09

    Study of magnetostrictive effects in the bulk superconductors is very essential and can give more knowledge about the effects like namely, flux pinning induced strain, pincushion distortions in the magnets and so on. Currently used electro mechanical sensors are magnetic field dependent and can only give the global stress/strain information but not the local stress/strains. But the information like radius position dependent strain and characterisation of shape distortion in non cylindrical magnets are interesting. Wavelength encoded multiplexed fiber Bragg Grating sensors inscribed in one fiber gives the possibility to measure magentostrictive effects spatially resolved in low temperature and high magnetic field. This paper specifies the design and technology requirements to adapt FBG sensors for such an application. Also reports the experiments demonstrate the properties of glass FBG at low temperature (4.2 K) and the results of strain measurement at 4.2 K/8 T. The sensor exhibits a linear wavelength change for the strain change.

  15. Method for formation of high quality back contact with screen-printed local back surface field

    DOEpatents

    Rohatgi, Ajeet; Meemongkolkiat, Vichai

    2010-11-30

    A thin silicon solar cell having a back dielectric passivation and rear contact with local back surface field is described. Specifically, the solar cell may be fabricated from a crystalline silicon wafer having a thickness from 50 to 500 micrometers. A barrier layer and a dielectric layer are applied at least to the back surface of the silicon wafer to protect the silicon wafer from deformation when the rear contact is formed. At least one opening is made to the dielectric layer. An aluminum contact that provides a back surface field is formed in the opening and on the dielectric layer. The aluminum contact may be applied by screen printing an aluminum paste having from one to 12 atomic percent silicon and then applying a heat treatment at 750 degrees Celsius.

  16. Application of locally one-dimensional semi-implicit scheme in phase-field equations

    NASA Astrophysics Data System (ADS)

    Cai, Dan; Zhang, Lijun; Du, Yong

    2015-07-01

    A locally one-dimensional (LOD) semi-implicit scheme is proposed for improving the numerical efficiency in the solving of parabolic partial differential equations in phase-field simulations. With LOD splitting, multi-dimensional parabolic problems can be numerically approximated by treating each of the spatial variables individually in single cycles. Additionally, each spatial variable can be treated in either real or Fourier space, allowing equations to be solved across a range of boundary conditions, including periodic, non-periodic, and even partial periodic. The proposed LOD semi-implicit scheme exhibits noticeable advantages over both explicit and implicit traditional schemes in terms of computational efficiency and accuracy, as demonstrated by two standard numerical tests. It is anticipated that future large-scale phase-field simulations will benefit greatly from the use of this LOD scheme.

  17. Intracellular localization of mevalonate-activating enzymes in plant cells

    PubMed Central

    Rogers, L. J.; Shah, S. P. J.; Goodwin, T. W.

    1966-01-01

    Mevalonate-activating enzymes are shown to be present in the chloroplasts of French-bean leaves. The chloroplast membrane is impermeable to mevalonic acid. Mevalonate-activating enzymes also appear to be found outside the chloroplast. These results support the view that terpenoid biosynthesis in the plant cell is controlled by a combination of enzyme segregation and specific membrane permeability. ImagesFig. 1.Fig. 2. PMID:5947149

  18. Hysteretic dynamics of active particles in a periodic orienting field

    PubMed Central

    Romensky, Maksym; Scholz, Dimitri; Lobaskin, Vladimir

    2015-01-01

    Active motion of living organisms and artificial self-propelling particles has been an area of intense research at the interface of biology, chemistry and physics. Significant progress in understanding these phenomena has been related to the observation that dynamic self-organization in active systems has much in common with ordering in equilibrium condensed matter such as spontaneous magnetization in ferromagnets. The velocities of active particles may behave similar to magnetic dipoles and develop global alignment, although interactions between the individuals might be completely different. In this work, we show that the dynamics of active particles in external fields can also be described in a way that resembles equilibrium condensed matter. It follows simple general laws, which are independent of the microscopic details of the system. The dynamics is revealed through hysteresis of the mean velocity of active particles subjected to a periodic orienting field. The hysteresis is measured in computer simulations and experiments on unicellular organisms. We find that the ability of the particles to follow the field scales with the ratio of the field variation period to the particles' orientational relaxation time, which, in turn, is related to the particle self-propulsion power and the energy dissipation rate. The collective behaviour of the particles due to aligning interactions manifests itself at low frequencies via increased persistence of the swarm motion when compared with motion of an individual. By contrast, at high field frequencies, the active group fails to develop the alignment and tends to behave like a set of independent individuals even in the presence of interactions. We also report on asymptotic laws for the hysteretic dynamics of active particles, which resemble those in magnetic systems. The generality of the assumptions in the underlying model suggests that the observed laws might apply to a variety of dynamic phenomena from the motion of

  19. Hysteretic dynamics of active particles in a periodic orienting field.

    PubMed

    Romensky, Maksym; Scholz, Dimitri; Lobaskin, Vladimir

    2015-07-01

    Active motion of living organisms and artificial self-propelling particles has been an area of intense research at the interface of biology, chemistry and physics. Significant progress in understanding these phenomena has been related to the observation that dynamic self-organization in active systems has much in common with ordering in equilibrium condensed matter such as spontaneous magnetization in ferromagnets. The velocities of active particles may behave similar to magnetic dipoles and develop global alignment, although interactions between the individuals might be completely different. In this work, we show that the dynamics of active particles in external fields can also be described in a way that resembles equilibrium condensed matter. It follows simple general laws, which are independent of the microscopic details of the system. The dynamics is revealed through hysteresis of the mean velocity of active particles subjected to a periodic orienting field. The hysteresis is measured in computer simulations and experiments on unicellular organisms. We find that the ability of the particles to follow the field scales with the ratio of the field variation period to the particles' orientational relaxation time, which, in turn, is related to the particle self-propulsion power and the energy dissipation rate. The collective behaviour of the particles due to aligning interactions manifests itself at low frequencies via increased persistence of the swarm motion when compared with motion of an individual. By contrast, at high field frequencies, the active group fails to develop the alignment and tends to behave like a set of independent individuals even in the presence of interactions. We also report on asymptotic laws for the hysteretic dynamics of active particles, which resemble those in magnetic systems. The generality of the assumptions in the underlying model suggests that the observed laws might apply to a variety of dynamic phenomena from the motion of

  20. Prostate segmentation with local binary patterns guided active appearance models

    NASA Astrophysics Data System (ADS)

    Ghose, Soumya; Oliver, Arnau; Martí, Robert; Lladó, Xavier; Freixenet, Jordi; Vilanova, Joan C.; Meriaudeau, Fabrice

    2011-03-01

    Real-time fusion of Magnetic Resonance (MR) and Trans Rectal Ultra Sound (TRUS) images aid in the localization of malignant tissues in TRUS guided prostate biopsy. Registration performed on segmented contours of the prostate reduces computational complexity and improves the multimodal registration accuracy. However, accurate and computationally efficient segmentation of the prostate in TRUS images could be challenging in the presence of heterogeneous intensity distribution inside the prostate gland, and other imaging artifacts like speckle noise, shadow regions and low Signal to Noise Ratio (SNR). In this work, we propose to enhance the texture features of the prostate region using Local Binary Patterns (LBP) for the propagation of a shape and appearance based statistical model to segment the prostate in a multi-resolution framework. A parametric model of the propagating contour is derived from Principal Component Analysis (PCA) of the prior shape and texture information of the prostate from the training data. The estimated parameters are then modified with the prior knowledge of the optimization space to achieve an optimal segmentation. The proposed method achieves a mean Dice Similarity Coefficient (DSC) value of 0.94+/-0.01 and a mean segmentation time of 0.68+/-0.02 seconds when validated with 70 TRUS images of 7 datasets in a leave-one-patient-out validation framework. Our method performs computationally efficient and accurate prostate segmentation in the presence of intensity heterogeneities and imaging artifacts.

  1. Information-Driven Active Audio-Visual Source Localization

    PubMed Central

    Schult, Niclas; Reineking, Thomas; Kluss, Thorsten; Zetzsche, Christoph

    2015-01-01

    We present a system for sensorimotor audio-visual source localization on a mobile robot. We utilize a particle filter for the combination of audio-visual information and for the temporal integration of consecutive measurements. Although the system only measures the current direction of the source, the position of the source can be estimated because the robot is able to move and can therefore obtain measurements from different directions. These actions by the robot successively reduce uncertainty about the source’s position. An information gain mechanism is used for selecting the most informative actions in order to minimize the number of actions required to achieve accurate and precise position estimates in azimuth and distance. We show that this mechanism is an efficient solution to the action selection problem for source localization, and that it is able to produce precise position estimates despite simplified unisensory preprocessing. Because of the robot’s mobility, this approach is suitable for use in complex and cluttered environments. We present qualitative and quantitative results of the system’s performance and discuss possible areas of application. PMID:26327619

  2. Information-Driven Active Audio-Visual Source Localization.

    PubMed

    Schult, Niclas; Reineking, Thomas; Kluss, Thorsten; Zetzsche, Christoph

    2015-01-01

    We present a system for sensorimotor audio-visual source localization on a mobile robot. We utilize a particle filter for the combination of audio-visual information and for the temporal integration of consecutive measurements. Although the system only measures the current direction of the source, the position of the source can be estimated because the robot is able to move and can therefore obtain measurements from different directions. These actions by the robot successively reduce uncertainty about the source's position. An information gain mechanism is used for selecting the most informative actions in order to minimize the number of actions required to achieve accurate and precise position estimates in azimuth and distance. We show that this mechanism is an efficient solution to the action selection problem for source localization, and that it is able to produce precise position estimates despite simplified unisensory preprocessing. Because of the robot's mobility, this approach is suitable for use in complex and cluttered environments. We present qualitative and quantitative results of the system's performance and discuss possible areas of application. PMID:26327619

  3. Optimization of collective enzyme activity via spatial localization

    NASA Astrophysics Data System (ADS)

    Buchner, Alexander; Tostevin, Filipe; Hinzpeter, Florian; Gerland, Ulrich

    2013-10-01

    The spatial organization of enzymes often plays a crucial role in the functionality and efficiency of enzymatic pathways. To fully understand the design and operation of enzymatic pathways, it is therefore crucial to understand how the relative arrangement of enzymes affects pathway function. Here we investigate the effect of enzyme localization on the flux of a minimal two-enzyme pathway within a reaction-diffusion model. We consider different reaction kinetics, spatial dimensions, and loss mechanisms for intermediate substrate molecules. Our systematic analysis of the different regimes of this model reveals both universal features and distinct characteristics in the phenomenology of these different systems. In particular, the distribution of the second pathway enzyme that maximizes the reaction flux undergoes a generic transition from co-localization with the first enzyme when the catalytic efficiency of the second enzyme is low, to an extended profile when the catalytic efficiency is high. However, the critical transition point and the shape of the extended optimal profile is significantly affected by specific features of the model. We explain the behavior of these different systems in terms of the underlying stochastic reaction and diffusion processes of single substrate molecules.

  4. Multichannel brain recordings in behaving Drosophila reveal oscillatory activity and local coherence in response to sensory stimulation and circuit activation

    PubMed Central

    Paulk, Angelique C.; Zhou, Yanqiong; Stratton, Peter; Liu, Li

    2013-01-01

    Neural networks in vertebrates exhibit endogenous oscillations that have been associated with functions ranging from sensory processing to locomotion. It remains unclear whether oscillations may play a similar role in the insect brain. We describe a novel “whole brain” readout for Drosophila melanogaster using a simple multichannel recording preparation to study electrical activity across the brain of flies exposed to different sensory stimuli. We recorded local field potential (LFP) activity from >2,000 registered recording sites across the fly brain in >200 wild-type and transgenic animals to uncover specific LFP frequency bands that correlate with: 1) brain region; 2) sensory modality (olfactory, visual, or mechanosensory); and 3) activity in specific neural circuits. We found endogenous and stimulus-specific oscillations throughout the fly brain. Central (higher-order) brain regions exhibited sensory modality-specific increases in power within narrow frequency bands. Conversely, in sensory brain regions such as the optic or antennal lobes, LFP coherence, rather than power, best defined sensory responses across modalities. By transiently activating specific circuits via expression of TrpA1, we found that several circuits in the fly brain modulate LFP power and coherence across brain regions and frequency domains. However, activation of a neuromodulatory octopaminergic circuit specifically increased neuronal coherence in the optic lobes during visual stimulation while decreasing coherence in central brain regions. Our multichannel recording and brain registration approach provides an effective way to track activity simultaneously across the fly brain in vivo, allowing investigation of functional roles for oscillations in processing sensory stimuli and modulating behavior. PMID:23864378

  5. Local fields in conductor surface electromigration: A first-principles study in the low-bias ballistic limit

    SciTech Connect

    Bevan, Kirk H; Zhu, Wenguang; Stocks, George Malcolm; Guo, Hong; Zhang, Zhenyu

    2012-01-01

    Utilizing first-principles quantum transport calculations, we investigate the role of local fields in conductor surface electromigration. A nanometer-thick Ag(100) thin film is adopted as our prototypical conductor, where we demonstrate the existence of intense local electric fields at atomic surface defects under an external bias. It is shown that such local fields can play an important role in driving surface electromigration and electrical breakdown. The intense fields originate from the relatively short (atomic-scale) screening lengths common to most elemental metals. This general short-range screening trend is established self-consistently within an intuitive picture of linear response electrostatics. The findings shed new light on the underlying physical origins of surface electromigration and point to the possibility of harnessing local fields to engineer electromigration at the nanoscale.

  6. Quasi-Adiabatic Quantum Computing Treated with c-Numbers Using the Local-Field Response

    NASA Astrophysics Data System (ADS)

    Tomaru, Tatsuya

    2016-03-01

    A computational method called the local-field response method is proposed, where spins evolve by responding to an effective field consisting of gradually decreasing external fields and spin-spin interactions, similarly to what is carried out in adiabatic quantum computing (AQC). This method is partly quantum-mechanical. That is, spins are treated as classical variables, but the response function of the spins to the effective field is determined a priori by referring to a quantum-mechanical calculation that was carried out for similar problems. This novel response function improves the performance of the ground state being maintained in the time evolution compared with the case without a priori information. The performance is numerically checked in an eight-qubit system by solving random-interaction problems of finding their ground states. The false probability decreases by about half as a result of using a priori information. The operation of this method is classical, but it has a quantum-mechanical advantage through a priori information. This method is practically useful because obtaining a complete quantum system is difficult as it stands.

  7. Local Autoencoding for Parameter Estimation in a Hidden Potts-Markov Random Field.

    PubMed

    Song, Sanming; Si, Bailu; Herrmann, J Michael; Feng, Xisheng

    2016-05-01

    A local-autoencoding (LAE) method is proposed for the parameter estimation in a Hidden Potts-Markov random field model. Due to sampling cost, Markov chain Monte Carlo methods are rarely used in real-time applications. Like other heuristic methods, LAE is based on a conditional independence assumption. It adapts, however, the parameters in a block-by-block style with a simple Hebbian learning rule. Experiments with given label fields show that the LAE is able to converge in far less time than required for a scan. It is also possible to derive an estimate for LAE based on a Cramer–Rao bound that is similar to the classical maximum pseudolikelihood method. As a general algorithm, LAE can be used to estimate the parameters in anisotropic label fields. Furthermore, LAE is not limited to the classical Potts model and can be applied to other types of Potts models by simple label field transformations and straightforward learning rule extensions. Experimental results on image segmentations demonstrate the efficiency and generality of the LAE algorithm. PMID:27019491

  8. Modeling of nonlinear microscopy of localized field enhancements in random metal nanostructures

    NASA Astrophysics Data System (ADS)

    Beermann, Jonas; Bozhevolnyi, Sergey I.; Coello, Victor

    2006-03-01

    Nonlinear microscopy of localized field enhancements in random metal nanostructures with a tightly focused laser beam scanning over a sample surface is modeled by making use of analytic representations of the Green dyadic in the near- and far-field regions, with the latter being approximated by the part describing the scattering via excitation of surface plasmon polaritons. The developed approach is applied to scanning second-harmonic (SH) microscopy of small gold spheres placed randomly on a gold surface. We calculate self-consistent fundamental harmonic (FH) and SH field distributions at the illuminated sample surface and, thereby, FH and SH images for different polarization configurations of the illuminating and detected fields. The simulated images bear close resemblance to the images obtained experimentally, exhibiting similar sensitivity to the wavelength and polarization, as well as sensitivity to the scattering configuration. We verify directly our conjecture that very bright spots in the SH images occur due to the spatial overlap of properly polarized FH and SH eigenmodes. Applications and further improvements of the developed model are discussed.

  9. Localized electric field induced transition and miniaturization of two-phase flow patterns inside microchannels.

    PubMed

    Sharma, Abhinav; Tiwari, Vijeet; Kumar, Vineet; Mandal, Tapas Kumar; Bandyopadhyay, Dipankar

    2014-10-01

    Strategic application of external electrostatic field on a pressure-driven two-phase flow inside a microchannel can transform the stratified or slug flow patterns into droplets. The localized electrohydrodynamic stress at the interface of the immiscible liquids can engender a liquid-dielectrophoretic deformation, which disrupts the balance of the viscous, capillary, and inertial forces of a pressure-driven flow to engender such flow morphologies. Interestingly, the size, shape, and frequency of the droplets can be tuned by varying the field intensity, location of the electric field, surface properties of the channel or fluids, viscosity ratio of the fluids, and the flow ratio of the phases. Higher field intensity with lower interfacial tension is found to facilitate the oil droplet formation with a higher throughput inside the hydrophilic microchannels. The method is successful in breaking down the regular pressure-driven flow patterns even when the fluid inlets are exchanged in the microchannel. The simulations identify the conditions to develop interesting flow morphologies, such as (i) an array of miniaturized spherical or hemispherical or elongated oil drops in continuous water phase, (ii) "oil-in-water" microemulsion with varying size and shape of oil droplets. The results reported can be of significance in improving the efficiency of multiphase microreactors where the flow patterns composed of droplets are preferred because of the availability of higher interfacial area for reactions or heat and mass exchange. PMID:25044128

  10. THE IMPRINT OF THE VERY LOCAL INTERSTELLAR MAGNETIC FIELD IN SIMULATED ENERGETIC NEUTRAL ATOM MAPS

    SciTech Connect

    Prested, C.; Schwadron, N.; Opher, M. E-mail: nathanas@bu.ed

    2010-06-10

    The interaction of the solar wind with the very local interstellar medium (VLISM) forms the boundaries of the heliosphere. A strong asymmetry of the heliosphere was found both directly by the Voyager probes and indirectly from measurements of the deflection of neutral hydrogen. The most likely source of this asymmetry is from the interstellar magnetic field, the properties of which are highly unconstrained. Energetic neutral atom (ENA) images will provide an additional method to view the heliosphere and infer the interstellar magnetic field. This paper investigates the imprint of the interstellar magnetic field on simulated energetic neutral atom all-sky maps. We show that a significant source of 0.5-1 keV ENAs may originate from the outside of the heliopause, if a strong suprathermal population exists in the VLISM. In simulations, a strong outer heliosheath ENA feature appears near the nose of the heliosphere. A weaker, complementary feature is also present consisting entirely of inner heliosheath ENAs. From this feature the direction of the interstellar magnetic field can be easily inferred.

  11. Carrier-density-wave transport and local internal electric field measurements in biased metal-oxide-semiconductor n-Si devices using contactless laser photo-carrier radiometry

    NASA Astrophysics Data System (ADS)

    Mandelis, Andreas; Pawlak, Micha; Shaughnessy, Derrick

    2004-11-01

    Laser infrared photo-carrier radiometry was used with an n-type Si metal-oxide-semiconductor (MOS) diode and with a Si-SiO2 structure with a transparent electrode and under external bias. Application of three-dimensional PCR theory yielded values of the minority carrier (hole) transport properties in the presence of the thus created local internal electric field at fixed frequencies. Furthermore, the internal electric field at fixed applied voltage was calculated. Under the combination of increased temperature and voltage, the sub-interface position of the carrier-density-wave centroid was found to depend on a trade-off between increased recombination lifetime and decreased ambipolar (conductivity) mobility. The ability of PCR to measure local internal electric fields by combining applied bias sweeps and frequency scans appears to pave the way towards the contactless reconstruction of depth profiles of these fields in active devices.

  12. Static potential and local color fields in unquenched lattice QCD{sub 3}

    SciTech Connect

    Trottier, Howard D.; Wong, Kit Yan

    2005-09-01

    String breaking by dynamical quarks in three-dimensional lattice QCD is analyzed through measurements of the potential and the local color-electric field strength generated by a static quark-antiquark pair. Simulations were done for unquenched SU(2) color with two flavors of staggered light quarks. An improved gluon action was used, which allows simulations to be done on coarse lattices, providing an extremely efficient means to access the large quark separations and long propagation times at which string breaking occurs. The static sources were generated using Wilson loop operators, hence no light valence quarks are present in the resulting trial states. Results give unambiguous evidence of string breaking. First the static potential is shown to saturate at twice the heavy-light meson mass at large separations. Then it is demonstrated that the local color-electric field strength in the region between the heavy quarks tends towards vacuum values at large separations, the first time that this most graphic effect of quark vacuum polarization on the confining flux-tube has been realized in lattice QCD. Implications of these results for unquenched simulations of four-dimensional QCD are drawn.

  13. Cascaded nonlinearity caused by local-field effects in the two-level atom

    SciTech Connect

    Dolgaleva, Ksenia; Boyd, Robert W.; Sipe, John E.

    2007-12-15

    Contributions to the fifth-order nonlinear optical susceptibility {chi}{sup (5)} of a collection of homogeneously broadened two-level atoms that scale as N{sup 2}({gamma}{sub at}{sup (3)}){sup 2} and N{sup 2}|{gamma}{sub at}{sup (3)}|{sup 2}, where {gamma}{sub at}{sup (3)} is the lower-order atomic hyperpolarizability and N is the atomic number density, are predicted theoretically. These 'cascaded' contributions are a consequence of local-field effects. We determine them from a fifth-order solution of the Lorentz-Maxwell-Bloch equations. They are missing from a straightforward generalization of Bloembergen's result for the local field correction to the second order nonlinearity, but are recovered by a careful application of his general approach. We find that at high atomic densities (N>10{sup 15} cm{sup -3}) the value of the cascaded third-order contribution can be as large as the 'direct' fifth-order term in the expression for the fifth-order susceptibility.

  14. Near-Field Sound Localization Based on the Small Profile Monaural Structure.

    PubMed

    Kim, Youngwoong; Kim, Keonwook

    2015-01-01

    The acoustic wave around a sound source in the near-field area presents unconventional properties in the temporal, spectral, and spatial domains due to the propagation mechanism. This paper investigates a near-field sound localizer in a small profile structure with a single microphone. The asymmetric structure around the microphone provides a distinctive spectral variation that can be recognized by the dedicated algorithm for directional localization. The physical structure consists of ten pipes of different lengths in a vertical fashion and rectangular wings positioned between the pipes in radial directions. The sound from an individual direction travels through the nearest open pipe, which generates the particular fundamental frequency according to the acoustic resonance. The Cepstral parameter is modified to evaluate the fundamental frequency. Once the system estimates the fundamental frequency of the received signal, the length of arrival and angle of arrival (AoA) are derived by the designed model. From an azimuthal distance of 3-15 cm from the outer body of the pipes, the extensive acoustic experiments with a 3D-printed structure show that the direct and side directions deliver average hit rates of 89% and 73%, respectively. The closer positions to the system demonstrate higher accuracy, and the overall hit rate performance is 78% up to 15 cm away from the structure body. PMID:26580618

  15. Localizing gauge fields on a topological Abelian string and the Coulomb law

    SciTech Connect

    Torrealba S, Rafael S.

    2010-07-15

    The confinement of electromagnetic field is studied in axial symmetrical, warped, six-dimensional brane world, using a recently proposed topological Abelian string-vortex solution as background. It was found, that the massless gauge field fluctuations follow four-dimensional Maxwell equations in the Lorenz gauge. The massless zero mode is localized when the thickness of the string vortex is less than 5{beta}/4{pi}e{sup 2}v{sup 2} and there are no other localized massless modes. There is also an infinite of nonlocalized massive Fourier modes, that follow four-dimensional Proca equations with a continuous spectrum. To compute the corrections to the Coulomb potential, a radial cutoff was introduced, in order to achieve a discrete mass spectrum. As a main result, a (R{sub o}/{beta}R{sup 2}) correction was found for the four-dimensional effective Coulomb law; the result is in correspondence with the observed behavior of the Coulomb potential at today's measurable distances.

  16. Relationship between microelectrode array impedance and chronic recording quality of single units and local field potentials.

    PubMed

    Jiang, JingLe; Willett, Francis R; Taylor, Dawn M

    2014-01-01

    Practical application of intracortical microelectrode technology is currently hindered by the inability to reliably record neuronal signals chronically. The precise mechanism of device failure is still under debate, but most likely includes some combination of tissue reaction, mechanical failure, and chronic material degradation. Impedance is a measure of the ease with which current flows through a working electrode under a driving voltage. Impedance has been hypothesized to provide information about an electrode's surrounding tissue reaction as well as chronic insulation degradation. In this study, we investigated the relationship between an electrode's impedance and its chronic recording performance as measured by the number of isolatable single units and the quality of local field potential recordings. Two 64-channel electrode arrays implanted in separate monkeys were assessed. We found no simple relationship between impedance and recording quality that held for both animals across all time periods. This suggests that future investigations on the topic should adopt a more fine-grained within-day and within-animal analysis. We also found new evidence from local field potential spatial correlation supporting the theory that insulation degradation is an important contributor to electrode failure. PMID:25570633

  17. Theoretical analysis of the microwave-drill near-field localized heating effect

    NASA Astrophysics Data System (ADS)

    Jerby, E.; Aktushev, O.; Dikhtyar, V.

    2005-02-01

    The microwave-drill principle [Jerby et al., Science 298, 587 (2002)] is based on a localized hot-spot effect induced by a near-field coaxial applicator. The microwave drill melts the nonmetallic material locally and penetrates mechanically into it to shape the hole. This paper presents a theoretical analysis of the thermal-runaway effect induced in front of the microwave drill. The model couples the Maxwell's and heat equations including the material's temperature-dependent properties. A finite-difference time-domain algorithm is applied in a two-time-scale numerical model. The simulation is demonstrated for mullite, and benchmarked in simplified cases. The results show a temperature rise of ˜103K/s up to 1300K within a hot spot confined to a ˜4-mm width (˜0.1 wavelength). The input-port response to this near-field effect is modeled by equivalent time-varying lumped-circuit elements. Besides the physical insight, this theoretical study provides computational tools for design and analysis of microwave drills and for their real-time monitoring and adaptive impedance matching.

  18. Near-Field Sound Localization Based on the Small Profile Monaural Structure

    PubMed Central

    Kim, Youngwoong; Kim, Keonwook

    2015-01-01

    The acoustic wave around a sound source in the near-field area presents unconventional properties in the temporal, spectral, and spatial domains due to the propagation mechanism. This paper investigates a near-field sound localizer in a small profile structure with a single microphone. The asymmetric structure around the microphone provides a distinctive spectral variation that can be recognized by the dedicated algorithm for directional localization. The physical structure consists of ten pipes of different lengths in a vertical fashion and rectangular wings positioned between the pipes in radial directions. The sound from an individual direction travels through the nearest open pipe, which generates the particular fundamental frequency according to the acoustic resonance. The Cepstral parameter is modified to evaluate the fundamental frequency. Once the system estimates the fundamental frequency of the received signal, the length of arrival and angle of arrival (AoA) are derived by the designed model. From an azimuthal distance of 3–15 cm from the outer body of the pipes, the extensive acoustic experiments with a 3D-printed structure show that the direct and side directions deliver average hit rates of 89% and 73%, respectively. The closer positions to the system demonstrate higher accuracy, and the overall hit rate performance is 78% up to 15 cm away from the structure body. PMID:26580618

  19. High frequency source localization in a shallow ocean sound channel using frequency difference matched field processing.

    PubMed

    Worthmann, Brian M; Song, H C; Dowling, David R

    2015-12-01

    Matched field processing (MFP) is an established technique for source localization in known multipath acoustic environments. Unfortunately, in many situations, particularly those involving high frequency signals, imperfect knowledge of the actual propagation environment prevents accurate propagation modeling and source localization via MFP fails. For beamforming applications, this actual-to-model mismatch problem was mitigated through a frequency downshift, made possible by a nonlinear array-signal-processing technique called frequency difference beamforming [Abadi, Song, and Dowling (2012). J. Acoust. Soc. Am. 132, 3018-3029]. Here, this technique is extended to conventional (Bartlett) MFP using simulations and measurements from the 2011 Kauai Acoustic Communications MURI experiment (KAM11) to produce ambiguity surfaces at frequencies well below the signal bandwidth where the detrimental effects of mismatch are reduced. Both the simulation and experimental results suggest that frequency difference MFP can be more robust against environmental mismatch than conventional MFP. In particular, signals of frequency 11.2 kHz-32.8 kHz were broadcast 3 km through a 106-m-deep shallow ocean sound channel to a sparse 16-element vertical receiving array. Frequency difference MFP unambiguously localized the source in several experimental data sets with average peak-to-side-lobe ratio of 0.9 dB, average absolute-value range error of 170 m, and average absolute-value depth error of 10 m. PMID:26723312

  20. Non-line-of-sight sound source localization using matched-field processing.

    PubMed

    Singh, Victor; Knisely, Katherine E; Yönak, Serdar H; Grosh, Karl; Dowling, David R

    2012-01-01

    Acoustic diffraction allows sound to travel around opaque objects and therefore may allow beyond-line-of-sight sensing of remote sound sources. This paper reports simulated and experimental results for localizing sound sources based on fully shadowed microphone array measurements. The generic geometry includes a point source, a solid 90° wedge, and a receiving array that lies entirely in the shadow defined by the source location and the wedge. Source localization performance is assessed via matched-field (MF) ambiguity surfaces as a function of receiving array configuration, and received signal-to-noise ratio for the Bartlett and minimum variance distortionless (MVD) MF processors. Here, the sound propagation model is developed from a Green's function integral treatment. A simple 16 element line array of microphones is tested in three mutually orthogonal orientations. The experiments were conducted using an approximate 50-to-1-scaled tabletop model of a blind city-street intersection and produced ambiguity surfaces from source frequencies between 17.5 and 19 kHz that were incoherently summed. The experimental results suggest that a sound source may be localized by the MVD processor when using fully shadowed arrays that have significant aperture parallel to the edge of the wedge. However, this performance is reduced significantly for signal-to-noise ratios below 40 dB. PMID:22280592

  1. Nociceptor activation and damage by pulsed E-fields

    NASA Astrophysics Data System (ADS)

    Nene, Deepti; Jiang, Nan; Rau, Kristofer K.; Richardson, Martin; Cooper, Brian Y.

    2006-05-01

    We assessed the capacity of ultrashort E-fields to activate rat cutaneous nociceptors. Experiments were conducted in vitro on nociceptive neurons representing hairy skin and glabrous skin. Electrical and optical recording methods were used to assess action potentials and membrane damage thresholds. Strength duration (SD) curves were formed for E-field pulses from 500 μsec to 350 ns. There were no differences in the SD time contant (taue (59 μsec) or ultrashort thresholds (129 V/cm at 350 ns) for hairy or glabrous skin nociceptors, for nociceptors with distinct geometry or for nociceptors expressing different combinations of voltage sensitive Na + channels (TTX s and TTX r Na v) or hyperpolarization activated channels (HCN; I H). Subthreshold activation was possible with high frequency pulsing at ultrashort durations (350 ns; 4,000 Hz). Relative to single pulse thresholds, activation threshold could be reduced over 50% by high frequency burst trains (4,000 Hz; 1-40 msec). Nociceptors were not damaged by E-field activation. Irreversible membrane disruption occurred at significantly higher field strength and varied by cell radius (3,266-4,240 V/cm, 350 ns, 40 Hz, 5 sec). Pulse frequency had no influence on acute membrane failure (10, 20, 40, 4,000 Hz; 5 sec).

  2. Coherence of heart rate variability and local physical fields in monitoring studies

    NASA Astrophysics Data System (ADS)

    Tuzhilkin, D. A.; Borodin, A. S.

    2015-11-01

    Technological advances have led to a substantial modification of the physical fields of the environment, which could affect the status of living organisms under their constant exposure. In this study, the activity of human cardiovascular system under the influence of a complex natural physical environmental factors investigated. The study was conducted on a representative homogeneous sample (44 persons aged 19 to 22 years) by simultaneous monitoring of electrocardiograms and natural physical fields in Tomsk (geomagnetic field, meteorological parameters - temperature, pressure and humidity, surface wind speed, the parameters of the Schumann resonance - amplitude, frequency and quality factor of the first four modes in the range of 6 to 32 Hz, the power spectral density infrasonic background in the range of from 0,5 to 32 Hz). It was shown that among the set of parameters of physical fields present field that can resonate in the functioning of the human organism. The greatest coherence with heart rate variability detect variations eastern component of the geomagnetic field.

  3. Self-organization of synchronous activity propagation in neuronal networks driven by local excitation.

    PubMed

    Bayati, Mehdi; Valizadeh, Alireza; Abbassian, Abdolhossein; Cheng, Sen

    2015-01-01

    Many experimental and theoretical studies have suggested that the reliable propagation of synchronous neural activity is crucial for neural information processing. The propagation of synchronous firing activity in so-called synfire chains has been studied extensively in feed-forward networks of spiking neurons. However, it remains unclear how such neural activity could emerge in recurrent neuronal networks through synaptic plasticity. In this study, we investigate whether local excitation, i.e., neurons that fire at a higher frequency than the other, spontaneously active neurons in the network, can shape a network to allow for synchronous activity propagation. We use two-dimensional, locally connected and heterogeneous neuronal networks with spike-timing dependent plasticity (STDP). We find that, in our model, local excitation drives profound network changes within seconds. In the emergent network, neural activity propagates synchronously through the network. This activity originates from the site of the local excitation and propagates through the network. The synchronous activity propagation persists, even when the local excitation is removed, since it derives from the synaptic weight matrix. Importantly, once this connectivity is established it remains stable even in the presence of spontaneous activity. Our results suggest that synfire-chain-like activity can emerge in a relatively simple way in realistic neural networks by locally exciting the desired origin of the neuronal sequence. PMID:26089794

  4. Nonperturbative measurement of the local magnetic field using pulsed polarimetry for fusion reactor conditions (invited)

    SciTech Connect

    Smith, Roger J.

    2008-10-15

    A novel diagnostic technique for the remote and nonperturbative sensing of the local magnetic field in reactor relevant plasmas is presented. Pulsed polarimetry [Patent No. 12/150,169 (pending)] combines optical scattering with the Faraday effect. The polarimetric light detection and ranging (LIDAR)-like diagnostic has the potential to be a local B{sub pol} diagnostic on ITER and can achieve spatial resolutions of millimeters on high energy density (HED) plasmas using existing lasers. The pulsed polarimetry method is based on nonlocal measurements and subtle effects are introduced that are not present in either cw polarimetry or Thomson scattering LIDAR. Important features include the capability of simultaneously measuring local T{sub e}, n{sub e}, and B{sub ||} along the line of sight, a resiliency to refractive effects, a short measurement duration providing near instantaneous data in time, and location for real-time feedback and control of magnetohydrodynamic (MHD) instabilities and the realization of a widely applicable internal magnetic field diagnostic for the magnetic fusion energy program. The technique improves for higher n{sub e}B{sub ||} product and higher n{sub e} and is well suited for diagnosing the transient plasmas in the HED program. Larger devices such as ITER and DEMO are also better suited to the technique, allowing longer pulse lengths and thereby relaxing key technology constraints making pulsed polarimetry a valuable asset for next step devices. The pulsed polarimetry technique is clarified by way of illustration on the ITER tokamak and plasmas within the magnetized target fusion program within present technological means.

  5. Mycorrhizal symbiosis and local adaptation in Aster amellus: a field transplant experiment.

    PubMed

    Pánková, Hana; Raabová, Jana; Münzbergová, Zuzana

    2014-01-01

    Many plant populations have adapted to local soil conditions. However, the role of arbuscular mycorrhizal fungi is often overlooked in this context. Only a few studies have used reciprocal transplant experiments to study the relationships between soil conditions, mycorrhizal colonisation and plant growth. Furthermore, most of the studies were conducted under controlled greenhouse conditions. However, long-term field experiments can provide more realistic insights into this issue. We conducted a five-year field reciprocal transplant experiment to study the relationships between soil conditions, arbuscular mycorrhizal fungi and plant growth in the obligate mycotrophic herb Aster amellus. We conducted this study in two regions in the Czech Republic that differ significantly in their soil nutrient content, namely Czech Karst (region K) and Ceske Stredohori (region S). Plants that originated from region S had significantly higher mycorrhizal colonisation than plants from region K, indicating that the percentage of mycorrhizal colonisation has a genetic basis. We found no evidence of local adaptation in Aster amellus. Instead, plants from region S outperformed the plants from region K in both target regions. Similarly, plants from region S showed more mycorrhizal colonisation in all cases, which was likely driven by the lower nutrient content in the soil from that region. Thus, plant aboveground biomass and mycorrhizal colonisation exhibited corresponding differences between the two target regions and regions of origin. Higher mycorrhizal colonisation in the plants from region with lower soil nutrient content (region S) in both target regions indicates that mycorrhizal colonisation is an adaptive trait. However, lower aboveground biomass in the plants with lower mycorrhizal colonisation suggests that the plants from region K are in fact maladapted by their low inherent mycorrhizal colonization. We conclude that including mycorrhizal symbiosis in local adaptation studies

  6. Nonperturbative measurement of the local magnetic field using pulsed polarimetry for fusion reactor conditions (invited).

    PubMed

    Smith, Roger J

    2008-10-01

    A novel diagnostic technique for the remote and nonperturbative sensing of the local magnetic field in reactor relevant plasmas is presented. Pulsed polarimetry [Patent No. 12/150,169 (pending)] combines optical scattering with the Faraday effect. The polarimetric light detection and ranging (LIDAR)-like diagnostic has the potential to be a local B(pol) diagnostic on ITER and can achieve spatial resolutions of millimeters on high energy density (HED) plasmas using existing lasers. The pulsed polarimetry method is based on nonlocal measurements and subtle effects are introduced that are not present in either cw polarimetry or Thomson scattering LIDAR. Important features include the capability of simultaneously measuring local T(e), n(e), and B(parallel) along the line of sight, a resiliency to refractive effects, a short measurement duration providing near instantaneous data in time, and location for real-time feedback and control of magnetohydrodynamic (MHD) instabilities and the realization of a widely applicable internal magnetic field diagnostic for the magnetic fusion energy program. The technique improves for higher n(e)B(parallel) product and higher n(e) and is well suited for diagnosing the transient plasmas in the HED program. Larger devices such as ITER and DEMO are also better suited to the technique, allowing longer pulse lengths and thereby relaxing key technology constraints making pulsed polarimetry a valuable asset for next step devices. The pulsed polarimetry technique is clarified by way of illustration on the ITER tokamak and plasmas within the magnetized target fusion program within present technological means. PMID:19044521

  7. Improved iris localization by using wide and narrow field of view cameras for iris recognition

    NASA Astrophysics Data System (ADS)

    Kim, Yeong Gon; Shin, Kwang Yong; Park, Kang Ryoung

    2013-10-01

    Biometrics is a method of identifying individuals by their physiological or behavioral characteristics. Among other biometric identifiers, iris recognition has been widely used for various applications that require a high level of security. When a conventional iris recognition camera is used, the size and position of the iris region in a captured image vary according to the X, Y positions of a user's eye and the Z distance between a user and the camera. Therefore, the searching area of the iris detection algorithm is increased, which can inevitably decrease both the detection speed and accuracy. To solve these problems, we propose a new method of iris localization that uses wide field of view (WFOV) and narrow field of view (NFOV) cameras. Our study is new as compared to previous studies in the following four ways. First, the device used in our research acquires three images, one each of the face and both irises, using one WFOV and two NFOV cameras simultaneously. The relation between the WFOV and NFOV cameras is determined by simple geometric transformation without complex calibration. Second, the Z distance (between a user's eye and the iris camera) is estimated based on the iris size in the WFOV image and anthropometric data of the size of the human iris. Third, the accuracy of the geometric transformation between the WFOV and NFOV cameras is enhanced by using multiple matrices of the transformation according to the Z distance. Fourth, the searching region for iris localization in the NFOV image is significantly reduced based on the detected iris region in the WFOV image and the matrix of geometric transformation corresponding to the estimated Z distance. Experimental results showed that the performance of the proposed iris localization method is better than that of conventional methods in terms of accuracy and processing time.

  8. Near-field-assisted localization: effect of size and filling factor of randomly distributed zinc oxide nanoneedles on multiple scattering and localization of light

    NASA Astrophysics Data System (ADS)

    Silies, Martin; Mascheck, Manfred; Leipold, David; Kollmann, Heiko; Schmidt, Slawa; Sartor, Janos; Yatsui, Takashi; Kitamura, Kokoro; Ohtsu, Motoicho; Kalt, Heinz; Runge, Erich; Lienau, Christoph

    2016-07-01

    We investigate the influence of the diameter and the filling factor of randomly arranged ZnO nanoneedles on the multiple scattering and localization of light in disordered dielectrics. Coherent, ultra-broadband second-harmonic (SH) microscopy is used to probe the spatial localization of light in representative nm-sized ZnO arrays of needles. We observe strong fluctuations of the SH intensity inside different ZnO needle geometries. Comparison of the SH intensity distributions with predictions based on a one-parameter scaling model indicate that SH fluctuations can be taken as a quantitative measure for the degree of localization. Interestingly, the strongest localization signatures are found for densely packed arrays of thin needles with diameters in the range of only 30 nm range, despite the small scattering cross section of these needles. FDTD simulations indicate that in this case coupling of electric near-fields between neighbouring needles governs the localization.

  9. Strain localization in carbonate rocks experimentally deformed in the ductile field

    NASA Astrophysics Data System (ADS)

    Rybacki, E.; Morales, L. F. G.; Dresen, G.

    2012-04-01

    The deformation of rocks in the Earth's crust is often localized, varying from brittle fault gauges in shallow environments to mylonites in ductile shear zones at greater depth. A number of theoretical, experimental, and field studies focused on the evolution and extend of brittle fault zones, but little is known so far about initiation of ductile shear zones. Strain localization in rocks deforming at high temperature and pressure may be induced by several physical, chemical, or structurally-related mechanisms. We performed simple and pure shear deformation experiments on carbonate rocks containing structural inhomogenities in the ductile deformation regime. The results may help to gain insight into the evolution of high temperature shear zones. As starting material we used cylindrical samples of coarse-grained Carrara marble containing one or two 1 mm thin artificially prepared sheets of fine-grained Solnhofen limestone, which act as soft inclusions under the applied experimental conditions. Length and diameter of the investigated solid and hollow cylinders were 10-20 mm and 10-15 mm, respectively. Samples were deformed in a Paterson-type gas deformation apparatus at 900° C temperature and confining pressures of 300 and 400 MPa. Three samples were deformed in axial compression at a bulk strain rate of 8x10-5 s-1to axial strains between 0.02 and 0.21 and 15 samples were twisted in torsion at a bulk shear strain rate of 2x10-4 s-1 to shear strains between 0.01 and 3.74. At low strain, specimens deformed axially and in torsion show minor strain hardening that is replaced by strain weakening at shear strains in excess of about 0.2. Peak shear stress at the imposed condition is about 20 MPa. Strain localized strongly within the weak inclusions as indicated by inhomogeneous bending of initially straight strain markers on sample jackets. Maximum strain concentration within inclusions with respect to the adjacent matrix was between 4 and 40, depending on total strain and

  10. Derivatives of the local ballooning growth rate with respect to surface label, field line label, and ballooning parameter

    SciTech Connect

    Hudson, S.R.

    2006-04-15

    Expressions for the derivative of the local ballooning growth rate with respect to surface label, field line label, and ballooning-parameter are presented. Such expressions lead to increased computational efficiency for ballooning stability applications.

  11. Environmental Education Objectives and Field Activities, Third Edition.

    ERIC Educational Resources Information Center

    Major, James M.; Cissell, Charles A.

    Contained in this teacher's guide are educational objectives and numerous field activity suggestions for environmental education. Part one deals with the total environmental education program, primarily developed for fifth grade students, but adaptable to any level, age six to adult. Sample objectives of an environmental education program, general…

  12. Environmental Education, Objectives and Field Activities, Fourth Edition.

    ERIC Educational Resources Information Center

    Major, James M.; Cissell, Charles A.

    Contained in this teacher's guide are educational objectives and numerous field activity suggestions for environmental education. Part One deals with the total environmental education program, primarily developed for fifth grade students, but adaptable to any level, age six to adult. Sample objectives of an environmental education program, general…

  13. The connection between stellar activity cycles and magnetic field topology

    NASA Astrophysics Data System (ADS)

    See, V.; Jardine, M.; Vidotto, A. A.; Donati, J.-F.; Boro Saikia, S.; Bouvier, J.; Fares, R.; Folsom, C. P.; Gregory, S. G.; Hussain, G.; Jeffers, S. V.; Marsden, S. C.; Morin, J.; Moutou, C.; do Nascimento, J. D.; Petit, P.; Waite, I. A.

    2016-08-01

    Zeeman Doppler imaging has successfully mapped the large-scale magnetic fields of stars over a large range of spectral types, rotation periods and ages. When observed over multiple epochs, some stars show polarity reversals in their global magnetic fields. On the Sun, polarity reversals are a feature of its activity cycle. In this paper, we examine the magnetic properties of stars with existing chromospherically determined cycle periods. Previous authors have suggested that cycle periods lie on multiple branches, either in the cycle period-Rossby number plane or the cycle period-rotation period plane. We find some evidence that stars along the active branch show significant average toroidal fields that exhibit large temporal variations while stars exclusively on the inactive branch remain dominantly poloidal throughout their entire cycle. This lends credence to the idea that different shear layers are in operation along each branch. There is also evidence that the short magnetic polarity switches observed on some stars are characteristic of the inactive branch while the longer chromospherically determined periods are characteristic of the active branch. This may explain the discrepancy between the magnetic and chromospheric cycle periods found on some stars. These results represent a first attempt at linking global magnetic field properties obtained form ZDI and activity cycles.

  14. Annual Report for 2003 Wild Horse Research and Field Activities

    USGS Publications Warehouse

    Ransom, Jason; Singer, Francis J.; Zeigenfuss, Linda C.

    2004-01-01

    This report is meant to highlight the activities of the 2003 field season, as well as to provide a general overview of the data collected. More in-depth data analysis will be conducted following the conclusion of each I phase of the research project, and in many cases will not be possible until several seasons of data are collected.

  15. Clinical Outcome and Characterization of Local Field Potentials in Holmes Tremor Treated with Pallidal Deep Brain Stimulation

    PubMed Central

    Ramirez-Zamora, Adolfo; Kaszuba, Brian C.; Gee, Lucy; Prusik, Julia; Danisi, Fabio; Shin, Damian; Pilitsis, Julie G

    2016-01-01

    Background Holmes tremor (HT) is an irregular, low-frequency rest tremor associated with prominent action and postural tremors. Currently, the most effective stereotactic target and neurophysiologic characterization of HT, specifically local field potentials (LFPs) are uncertain. We present the outcome, intraoperative neurophysiologic analysis with characterization of LFPs in a patient managed with left globus pallidus interna deep brain stimulation (Gpi DBS). Case Report A 24-year-old male underwent left Gpi DBS for medically refractory HT. LFPs demonstrated highest powers in the delta range in Gpi. At the 6-month follow-up, a 90% reduction in tremor was observed. Discussion Pallidal DBS should be considered as an alternative target for management of refractory HT. LFP demonstrated neuronal activity associated with higher power in the delta region, similarly seen in patients with generalized dystonia. PMID:27441097

  16. A hierarchy of timescales explains distinct effects of local inhibition of primary visual cortex and frontal eye fields.

    PubMed

    Cocchi, Luca; Sale, Martin V; L Gollo, Leonardo; Bell, Peter T; Nguyen, Vinh T; Zalesky, Andrew; Breakspear, Michael; Mattingley, Jason B

    2016-01-01

    Within the primate visual system, areas at lower levels of the cortical hierarchy process basic visual features, whereas those at higher levels, such as the frontal eye fields (FEF), are thought to modulate sensory processes via feedback connections. Despite these functional exchanges during perception, there is little shared activity between early and late visual regions at rest. How interactions emerge between regions encompassing distinct levels of the visual hierarchy remains unknown. Here we combined neuroimaging, non-invasive cortical stimulation and computational modelling to characterize changes in functional interactions across widespread neural networks before and after local inhibition of primary visual cortex or FEF. We found that stimulation of early visual cortex selectively increased feedforward interactions with FEF and extrastriate visual areas, whereas identical stimulation of the FEF decreased feedback interactions with early visual areas. Computational modelling suggests that these opposing effects reflect a fast-slow timescale hierarchy from sensory to association areas. PMID:27596931

  17. Boosting Local Field Enhancement by on-Chip Nanofocusing and Impedance-Matched Plasmonic Antennas.

    PubMed

    Zenin, Vladimir A; Andryieuski, Andrei; Malureanu, Radu; Radko, Ilya P; Volkov, Valentyn S; Gramotnev, Dmitri K; Lavrinenko, Andrei V; Bozhevolnyi, Sergey I

    2015-12-01

    Strongly confined surface plasmon-polariton modes can be used for efficiently delivering the electromagnetic energy to nanosized volumes by reducing the cross sections of propagating modes far beyond the diffraction limit, that is, by nanofocusing. This process results in significant local-field enhancement that can advantageously be exploited in modern optical nanotechnologies, including signal processing, biochemical sensing, imaging, and spectroscopy. Here, we propose, analyze, and experimentally demonstrate on-chip nanofocusing followed by impedance-matched nanowire antenna excitation in the end-fire geometry at telecom wavelengths. Numerical and experimental evidence of the efficient excitation of dipole and quadrupole (dark) antenna modes are provided, revealing underlying physical mechanisms and analogies with the operation of plane-wave Fabry-Pérot interferometers. The unique combination of efficient nanofocusing and nanoantenna resonant excitation realized in our experiments offers a major boost to the field intensity enhancement up to ∼12000, with the enhanced field being evenly distributed over the gap volume of 30 × 30 × 10 nm(3), and promises thereby a variety of useful on-chip functionalities within sensing, nonlinear spectroscopy and signal processing. PMID:26551324

  18. Sensitivity of resistive and Hall measurements to local inhomogeneities: Finite-field, intensity, and area corrections

    NASA Astrophysics Data System (ADS)

    Koon, Daniel W.; Wang, Fei; Petersen, Dirch Hjorth; Hansen, Ole

    2014-10-01

    We derive exact, analytic expressions for the sensitivity of sheet resistance and Hall sheet resistance measurements to local inhomogeneities for the cases of nonzero magnetic fields, strong perturbations, and perturbations over a finite area, extending our earlier results on weak perturbations. We express these sensitivities for conductance tensor components and for other charge transport quantities. Both resistive and Hall sensitivities, for a van der Pauw specimen in a finite magnetic field, are a superposition of the zero-field sensitivities to both sheet resistance and Hall sheet resistance. Strong perturbations produce a nonlinear correction term that depends on the strength of the inhomogeneity. Solution of the specific case of a finite-sized circular inhomogeneity coaxial with a circular specimen suggests a first-order correction for the general case. Our results are confirmed by computer simulations on both a linear four-point probe array on a large circular disc and a van der Pauw square geometry. Furthermore, the results also agree well with Náhlík et al. published experimental results for physical holes in a circular copper foil disc.

  19. Morphogenetic fields in embryogenesis, regeneration, and cancer: Non-local control of complex patterning

    PubMed Central

    Levin, Michael

    2012-01-01

    Establishment of shape during embryonic development, and the maintenance of shape against injury or tumorigenesis, requires constant coordination of cell behaviors toward the patterning needs of the host organism. Molecular cell biology and genetics have made great strides in understanding the mechanisms that regulate cell function. However, generalized rational control of shape is still largely beyond our current capabilities. Significant instructive signals function at long range to provide positional information and other cues to regulate organism-wide systems properties like anatomical polarity and size control. Is complex morphogenesis best understood as the emergent property of local cell interactions, or as the outcome of a computational process that is guided by a physically-encoded map or template of the final goal state? Here I review recent data and molecular mechanisms relevant to morphogenetic fields: large-scale systems of physical properties that have been proposed to store patterning information during embryogenesis, regenerative repair, and cancer suppression that ultimately controls anatomy. Placing special emphasis on the role of endogenous bioelectric signals as an important component of the morphogenetic field, I speculate on novel approaches for the computational modeling and control of these fields with applications to synthetic biology, regenerative medicine, and evolutionary developmental biology. PMID:22542702

  20. Tumor Treating Fields Perturb the Localization of Septins and Cause Aberrant Mitotic Exit

    PubMed Central

    Holtzman, Talia S.; Lee, Sze Xian; Wong, Eric T.; Swanson, Kenneth D.

    2015-01-01

    The anti-tumor effects of chemotherapy and radiation are thought to be mediated by triggering G1/S or G2/M cell cycle checkpoints, while spindle poisons, such as paclitaxel, block metaphase exit by initiating the spindle assembly checkpoint. In contrast, we have found that 150 kilohertz (kHz) alternating electric fields, also known as Tumor Treating Fields (TTFields), perturbed cells at the transition from metaphase to anaphase. Cells exposed to the TTFields during mitosis showed normal progression to this point, but exhibited uncontrolled membrane blebbing that coincided with metaphase exit. The ability of such alternating electric fields to affect cellular physiology is likely to be dependent on their interactions with proteins possessing high dipole moments. The mitotic Septin complex consisting of Septin 2, 6 and 7, possesses a high calculated dipole moment of 2711 Debyes (D) and plays a central role in positioning the cytokinetic cleavage furrow, and governing its contraction during ingression. We showed that during anaphase, TTFields inhibited Septin localization to the anaphase spindle midline and cytokinetic furrow, as well as its association with microtubules during cell attachment and spreading on fibronectin. After aberrant metaphase exit as a consequence of TTFields exposure, cells exhibited aberrant nuclear architecture and signs of cellular stress including an overall decrease in cellular proliferation, followed by apoptosis that was strongly influenced by the p53 mutational status. Thus, TTFields are able to diminish cell proliferation by specifically perturbing key proteins involved in cell division, leading to mitotic catastrophe and subsequent cell death. PMID:26010837

  1. Field Dependence-Field Independence Cognitive Style, Gender, Career Choice and Academic Achievement of Secondary School Students in Emohua Local Government Area of Rivers State

    ERIC Educational Resources Information Center

    Onyekuru, Bruno Uchenna

    2015-01-01

    This is a descriptive study that investigated the relationships among field dependence-field independence cognitive style and gender, career choice and academic achievement of secondary school students in Emohua Local Government Area of Rivers State, Nigeria. From the initial sample of 320 senior secondary school one (SS1) students drawn from the…

  2. HERSCHEL/SPIRE SUBMILLIMETER SPECTRA OF LOCAL ACTIVE GALAXIES {sup ,}

    SciTech Connect

    Pereira-Santaella, Miguel; Spinoglio, Luigi; Busquet, Gemma; Wilson, Christine D.; Schirm, Maximilien R. P.; Glenn, Jason; Kamenetzky, Julia; Rangwala, Naseem; Isaak, Kate G.; Baes, Maarten; Barlow, Michael J.; Boselli, Alessandro; Cooray, Asantha; Cormier, Diane

    2013-05-01

    We present the submillimeter spectra from 450 to 1550 GHz of 11 nearby active galaxies observed with the SPIRE Fourier Transform Spectrometer (SPIRE/FTS) on board Herschel. We detect CO transitions from J{sub up} = 4 to 12, as well as the two [C I] fine structure lines at 492 and 809 GHz and the [N II]1461 GHz line. We used radiative transfer models to analyze the observed CO spectral line energy distributions. The FTS CO data were complemented with ground-based observations of the low-J CO lines. We found that the warm molecular gas traced by the mid-J CO transitions has similar physical conditions (n{sub H{sub 2}}{approx} 10{sup 3.2}-10{sup 3.9} cm{sup -3} and T{sub kin} {approx} 300-800 K) in most of our galaxies. Furthermore, we found that this warm gas is likely producing the mid-IR rotational H{sub 2} emission. We could not determine the specific heating mechanism of the warm gas, however, it is possibly related to the star formation activity in these galaxies. Our modeling of the [C I] emission suggests that it is produced in cold (T{sub kin} < 30 K) and dense (n{sub H{sub 2}}>10{sup 3} cm{sup -3}) molecular gas. Transitions of other molecules are often detected in our SPIRE/FTS spectra. The HF J = 1-0 transition at 1232 GHz is detected in absorption in UGC 05101 and in emission in NGC 7130. In the latter, near-infrared pumping, chemical pumping, or collisional excitation with electrons are plausible excitation mechanisms likely related to the active galactic nucleus of this galaxy. In some galaxies, few H{sub 2}O emission lines are present. Additionally, three OH{sup +} lines at 909, 971, and 1033 GHz are identified in NGC 7130.

  3. The insulin receptor activation process involves localized conformational changes.

    PubMed

    Baron, V; Kaliman, P; Gautier, N; Van Obberghen, E

    1992-11-15

    The molecular process by which insulin binding to the receptor alpha-subunit induces activation of the receptor beta-subunit with ensuing substrate phosphorylation remains unclear. In this study, we aimed at approaching this molecular mechanism of signal transduction and at delineating the cytoplasmic domains implied in this process. To do this, we used antipeptide antibodies to the following sequences of the receptor beta-subunit: (i) positions 962-972 in the juxtamembrane domain, (ii) positions 1247-1261 at the end of the kinase domain, and (iii) positions 1294-1317 and (iv) positions 1309-1326, both in the receptor C terminus. We have previously shown that insulin binding to its receptor induces a conformational change in the beta-subunit C terminus. Here, we demonstrate that receptor autophosphorylation induces an additional conformational change. This process appears to be distinct from the one produced by ligand binding and can be detected in at least three different beta-subunit regions: the juxtamembrane domain, the kinase domain, and the C terminus. Hence, the cytoplasmic part of the receptor beta-subunit appears to undergo an extended conformational change upon autophosphorylation. By contrast, the insulin-induced change does not affect the juxtamembrane domain 962-972 nor the kinase domain 1247-1261 and may be limited to the receptor C terminus. Further, we show that the hormone-dependent conformational change is maintained in a kinase-deficient receptor due to a mutation at lysine 1018. Therefore, during receptor activation, the ligand-induced change could precede ATP binding and receptor autophosphorylation. We propose that insulin binding leads to a transient receptor form that may allow ATP binding and, subsequently, autophosphorylation. The second conformational change could unmask substrate-binding sites and stabilize the receptor in an active conformation. PMID:1331080

  4. Local or distributed activation? The view from biology

    NASA Astrophysics Data System (ADS)

    Reimers, Mark

    2011-06-01

    There is considerable disagreement among connectionist modellers over whether to represent distinct properties by distinct nodes of a network or whether properties should be represented by patterns of activity across all nodes. This paper draws on the literature of neuroscience to say that a more subtle way of describing how different brain regions contribute to a behaviour, in terms of individual learning and in terms of degrees of importance, may render the current debate moot: both sides of the 'localist' versus 'distributed' debate emphasise different aspects of biology.

  5. M dwarfs in the Local Milky Way: The Field Low-Mass Stellar Luminosity and Mass Functions

    SciTech Connect

    Bochanski, John J., Jr.; /Washington U., Seattle, Astron. Dept.

    2006-06-01

    Modern sky surveys, such as the Sloan Digital Sky Survey (SDSS) and the Two-Micron All Sky Survey, have revolutionized how Astronomy is done. With millions of photometric and spectroscopic observations, global observational properties can be studied with unprecedented statistical significance. Low-mass stars dominate the local Milky Way, with tens of millions observed by SDSS within a few kpc. Thus, they make ideal tracers of the Galactic potential, and the thin and thick disks. In this thesis dissertation, I present my efforts to characterize the local low-mass stellar population, using a collection of observations from the Sloan Digital Sky Survey (SDSS). First, low-mass stellar template spectra were constructed from the co-addition of thousands of SDSS spectroscopic observations. These template spectra were used to quantify the observable changes introduced by chromospheric activity and metallicity. Furthermore, the average ugriz colors were measured as a function of spectral type. Next, the local kinematic structure of the Milky Way was quantified, using a special set of SDSS spectroscopic observations. Combining proper motions and radial velocities (measured using the spectral templates), along with distances, the full UVW space motions of over 7000 low-mass stars along one line of sight were computed. These stars were also separated kinematically to investigate other observational differences between the thin and thick disks. Finally, this dissertation details a project designed to measure the luminosity and mass functions of low-mass stars. Using a new technique optimized for large surveys, the field luminosity function (LF) and local stellar density profile are measured simultaneously. The sample size used to estimate the LF is nearly three orders of magnitude larger than any previous study, offering a definitive measurement of this quantity. The observed LF is transformed into a mass function (MF) and compared to previous studies.

  6. Active thermal extraction of near-field thermal radiation

    NASA Astrophysics Data System (ADS)

    Ding, D.; Kim, T.; Minnich, A. J.

    2016-02-01

    Radiative heat transport between materials supporting surface-phonon polaritons is greatly enhanced when the materials are placed at subwavelength separation as a result of the contribution of near-field surface modes. However, the enhancement is limited to small separations due to the evanescent decay of the surface waves. In this work, we propose and numerically demonstrate an active scheme to extract these modes to the far field. Our approach exploits the monochromatic nature of near-field thermal radiation to drive a transition in a laser gain medium, which, when coupled with external optical pumping, allows the resonant surface mode to be emitted into the far field. Our study demonstrates an approach to manipulate thermal radiation that could find applications in thermal management.

  7. Chromospheric magnetic fields of an active region filament

    NASA Astrophysics Data System (ADS)

    Xu, Z.; Solanki, S.; Lagg, A.

    2012-06-01

    Vector magnetic fields of an active region filament are co-spatially and co-temporally mapped in photosphere and upper chromosphere, by using spectro-polarimetric observations made by Tenerife Infrared Polarimeter (TIP II) at the German Vacuum Tower Telescope (VTT). A Zeeman-based ME inversion is performed on the full Stokes vectors of both the photospheric Si I 1082.7 nm and the chromospheric He I 1083.0 nm lines. We found that the strong magnetic fields, with the field strength of 600 - 800 G in the He I line formation height, are not uncommon among AR filaments. But such strong magnetic field is not always found in AR filaments.

  8. Supportive environments for physical activity and the local government agenda: a South Australian example.

    PubMed

    MacDougall, Colin; Wright, Cheryl; Atkinson, Rick

    2002-01-01

    In the promotion of moderate physical activity it is increasingly argued that a supportive physical environment is a key factor, and that local government is ideally placed to play an important role. This study reports on the factors that led one local government to take such a leading role. A semi-structured interview was conducted to find out why a chief executive officer of a local government decided that the creation of supportive environments for physical activity was the core business of council. The results show that key ingredients were that local government should take a strategic rather than an operational focus on the issue, that there should be open organisational structures to allow the various functions of local government to work together, and that there must be appropriate leadership. The findings suggest ways for engaging local government as a key partner in promoting supportive environments that are consistent with literature on policy, organisational structure and leadership theory. PMID:12046147

  9. Protein kinase A activation enhances β-catenin transcriptional activity through nuclear localization to PML bodies.

    PubMed

    Zhang, Mei; Mahoney, Emilia; Zuo, Tao; Manchanda, Parmeet K; Davuluri, Ramana V; Kirschner, Lawrence S

    2014-01-01

    The Protein Kinase A (PKA) and Wnt signaling cascades are fundamental pathways involved in cellular development and maintenance. In the osteoblast lineage, these pathways have been demonstrated functionally to be essential for the production of mineralized bone. Evidence for PKA-Wnt crosstalk has been reported both during tumorigenesis and during organogenesis, and the nature of the interaction is thought to rely on tissue and cell context. In this manuscript, we analyzed bone tumors arising from mice with activated PKA caused by mutation of the PKA regulatory subunit Prkar1a. In primary cells from these tumors, we observed relocalization of β-catenin to intranuclear punctuate structures, which were identified as PML bodies. Cellular redistribution of β-catenin could be recapitulated by pharmacologic activation of PKA. Using 3T3-E1 pre-osteoblasts as a model system, we found that PKA phosphorylation sites on β-catenin were required for nuclear re-localization. Further, β-catenin's transport to the nucleus was accompanied by an increase in canonical Wnt-dependent transcription, which also required the PKA sites. PKA-Wnt crosstalk in the cells was bi-directional, including enhanced interactions between β-catenin and the cAMP-responsive element binding protein (CREB) and transcriptional crosstalk between the Wnt and PKA signaling pathways. Increases in canonical Wnt/β-catenin signaling were associated with a decrease in the activity of the non-canonical Wnt/Ror2 pathway, which has been shown to antagonize canonical Wnt signaling. Taken together, this study provides a new understanding of the complex regulation of the subcellular distribution of β-catenin and its differential protein-protein interaction that can be modulated by PKA signaling. PMID:25299576

  10. Introduction and pinning of domain walls in 50 nm NiFe constrictions using local and external magnetic fields

    NASA Astrophysics Data System (ADS)

    Zahnd, G.; Pham, V. T.; Marty, A.; Jamet, M.; Beigné, C.; Notin, L.; Vergnaud, C.; Rortais, F.; Vila, L.; Attané, J.-P.

    2016-05-01

    We study domain wall injection in 100 nm wide NiFe nanowires, followed by domain wall propagation and pinning on 50 nm wide constrictions. The injection is performed using local and external magnetic fields. Using several nucleation pad geometries, we show that at these small dimensions the use of an external field only does not allow obtaining a reproducible injection/pinning process. However, the use of an additional local field, created by an Oersted line, allows to nucleate a reversed domain at zero external applied field. Then, an external field of 5 mT enables the domain wall to propagate far from the Oersted line, and the pinning occurs reproducibly. We also show that notwithstanding the reproducibility of the pinning process, the depinning field is found to be stochastic, following a bimodal distribution. Using micromagnetic simulation we link two different DW configurations, vortex and transverse, to the two typical depinning fields.

  11. Adaptive wave field synthesis for active sound field reproduction: experimental results.

    PubMed

    Gauthier, Philippe-Aubert; Berry, Alain

    2008-04-01

    Sound field reproduction has applications in music reproduction, spatial audio, sound environment reproduction, and experimental acoustics. Sound field reproduction can be used to artificially reproduce the spatial character of natural hearing. The objective is then to reproduce a sound field in a real reproduction environment. Wave field synthesis (WFS) is a known open-loop technology which assumes that the reproduction environment is anechoic. The room response thus reduces the quality of the physical sound field reproduction by WFS. In recent research papers, adaptive wave field synthesis (AWFS) was defined as a potential solution to compensate for these quality reductions from which WFS objective performance suffers. In this paper, AWFS is experimentally investigated as an active sound field reproduction system with a limited number of reproduction error sensors to compensate for the response of the listening environment. Two digital signal processing algorithms for AWFS are used for comparison purposes, one of which is based on independent radiation mode control. AWFS performed propagating sound field reproduction better than WFS in three tested reproduction spaces (hemianechoic chamber, standard laboratory space, and reverberation chamber). PMID:18397007

  12. Relationship between local molecular field theory and density functional theory for non-uniform liquids.

    PubMed

    Archer, A J; Evans, R

    2013-01-01

    The local molecular field theory (LMF) developed by Weeks and co-workers has proved successful for treating the structure and thermodynamics of a variety of non-uniform liquids. By reformulating LMF in terms of one-body direct correlation functions we recast the theory in the framework of classical density functional theory (DFT). We show that the general LMF equation for the effective reference potential φ(R)(r) follows directly from the standard mean-field DFT treatment of attractive interatomic forces. Using an accurate (fundamental measures) DFT for the non-uniform hard-sphere reference fluid we determine φ(R)(r) for a hard-core Yukawa liquid adsorbed at a planar hard wall. In the approach to bulk liquid-gas coexistence we find the effective potentials exhibit rich structure that can include damped oscillations at large distances from the wall as well as the repulsive hump near the wall required to generate the low density "gas" layer characteristic of complete drying. We argue that it would be difficult to obtain the same level of detail from other (non-DFT based) implementations of LMF. LMF emphasizes the importance of making an intelligent division of the interatomic pair potential of the full system into a reference part and a remainder that can be treated in mean-field approximation. We investigate different divisions for an exactly solvable one-dimensional model where the pair potential has a hard-core plus a linear attractive tail. Results for the structure factor and the equation of state of the uniform fluid show that including a significant portion of the attraction in the reference system can be much more accurate than treating the full attractive tail in mean-field approximation. We discuss further aspects of the relationship between LMF and DFT. PMID:23298050

  13. Fluctuations of local electric field and dipole moments in water between metal walls

    NASA Astrophysics Data System (ADS)

    Takae, Kyohei; Onuki, Akira

    2015-10-01

    We examine the thermal fluctuations of the local electric field Ek loc and the dipole moment μk in liquid water at T = 298 K between metal walls in electric field applied in the perpendicular direction. We use analytic theory and molecular dynamics simulation. In this situation, there is a global electrostatic coupling between the surface charges on the walls and the polarization in the bulk. Then, the correlation function of the polarization density pz(r) along the applied field contains a homogeneous part inversely proportional to the cell volume V. Accounting for the long-range dipolar interaction, we derive the Kirkwood-Fröhlich formula for the polarization fluctuations when the specimen volume v is much smaller than V. However, for not small v/V, the homogeneous part comes into play in dielectric relations. We also calculate the distribution of Ek loc in applied field. As a unique feature of water, its magnitude | Ek loc | obeys a Gaussian distribution with a large mean value E0 ≅ 17 V/nm, which arises mainly from the surrounding hydrogen-bonded molecules. Since |μk|E0 ˜ 30kBT, μk becomes mostly parallel to Ek loc . As a result, the orientation distributions of these two vectors nearly coincide, assuming the classical exponential form. In dynamics, the component of μk(t) parallel to Ek loc ( t ) changes on the time scale of the hydrogen bonds ˜5 ps, while its smaller perpendicular component undergoes librational motions on time scales of 0.01 ps.

  14. How Does the Local Electrostatic Field Influence Emitted Wavelengths and Bioluminescent Intensities of Modified Heteroaromatic Luciferins?

    PubMed

    Zhou, Jian-Ge; Williams, Quinton L; Walters, Wilbur; Deng, Zhen-Yan

    2015-08-20

    The firefly chromophore, oxyluciferin, is in the pocket of the firefly luciferase and is surrounded by the side-chains of some amino acid residues. The charged residues produce the local electrostatic field (LEF) around the oxyluciferin. The emitted wavelengths and intensities of the oxyluciferin and its heterocyclic analogs under the LEF are examined. The common overlapping volumes of the HOMO and LUMO explain why the oscillator strengths vary under the LEF. Three average Ex change rates of the first excited energy are introduced to measure what luciferins are more sensitive to the LEF. The first excited energies and intensities in two enzymatic-like microenvironments are simulated via the LEF. The oscillator strengths and the net electric charges of the O6' and the O4 are applied to explain the experimental bioluminescent intensities. PMID:26218458

  15. Entanglement negativity after a local quantum quench in conformal field theories

    NASA Astrophysics Data System (ADS)

    Wen, Xueda; Chang, Po-Yao; Ryu, Shinsei

    2015-08-01

    We study the time evolution of the entanglement negativity after a local quantum quench in (1 + 1)-dimensional conformal field theories (CFTs), which we introduce by suddenly joining two initially decoupled CFTs at their end points. We calculate the negativity evolution for both adjacent intervals and disjoint intervals explicitly. For two adjacent intervals, the entanglement negativity grows logarithmically in time right after the quench. After developing a plateau-like feature, the entanglement negativity drops to the ground-state value. For the case of two spatially separated intervals, a light-cone behavior is observed in the negativity evolution; in addition, a long-range entanglement, which is independent of the distance between two intervals, can be created. Our results agree with the heuristic picture that quasiparticles, which carry entanglement, are emitted from the joining point and propagate freely through the system. Our analytical results are confirmed by numerical calculations based on a critical harmonic chain.

  16. Electronic scattering of pseudo-magnetic field induced by local bump in graphene

    NASA Astrophysics Data System (ADS)

    Yang, Mou; Cui, Yan; Wang, Rui-Qiang; Zhao, Hong-Bo

    2012-10-01

    We investigated the electronic scattering properties of a local bump strain in graphene sheet in frame of Born approximation. The differential scattering cross section is a function of outgoing and incident angles and has the six-fold rotational symmetry with respect to both angles. The incident plane wave is scattered into two backward fan-waves in different directions in low energy limit and is split into two branches spanning the angle reversely proportional to the incident wavevector k in high energy limit. The total scattering cross section depends on incident wavevector by the form k5 in the former limit, while it is independent of k and sensitive to the incident orientation in the latter limit. We explained these features using the symmetry of the strain-induced pseudo-magnetic field.

  17. On the local standard of rest. [comoving with young objects in gravitational field of spiral galaxies

    NASA Technical Reports Server (NTRS)

    Yuan, C.

    1983-01-01

    Under the influence of a spiral gravitational field, there should be differences among the mean motions of different types of objects with different dispersion velocities in a spiral galaxy. The old stars with high dispersion velocity should have essentially no mean motion normal to the galactic rotation. On the other hand, young objects and interstellar gas may be moving relative to the old stars at a velocity of a few kilometer per second in both the radial (galacto-centric), and circular directions, depending on the spiral model adopted. Such a velocity is usually referred as the systematic motion or the streaming motion. The conventionally adopted local standard of rest is indeed co-moving with the young objects of the solar vicinity. Therefore, it has a net systematic motion with respect to the circular motion of an equilibrium galactic model, defined by the old stars. Previously announced in STAR as N83-24443

  18. Liquid Crystal Switching Response by Localized Surface Plasmon Induced Electric Fields

    NASA Astrophysics Data System (ADS)

    Nuno, Zachary; Hirst, Linda; Ghosh, Sayantani

    2013-03-01

    We investigate the effect of electric fields induced by localized surface plasmons (LSPs) from gold nanoparticles (AuNPs) on the director of a nematic liquid crystal (LC). We deposit LC thin films on a self-assembled AuNP layer and excite the LSPs in the AuNPs using 530 nm excitation light. Using polarized optical microscopy we follow the birefringence of the LC film as the excitation is turned on and off and observe the homeotropic alignment of the LC change to planar. This realignment response is observed to be dependent on the excitation wavelength, excitation power, and temperature; occurring only within 1 degree Celsius of the LC phase transition from nematic to isotropic. This work was funded by UC Merced GRC Summer Fellowship.

  19. A Dream of Yukawa — Non-Local Fields out of Non-Commutative Spacetime —

    NASA Astrophysics Data System (ADS)

    Naka, Shigefumi; Toyoda, Haruki; Takanashi, Takahiro; Umezawa, Eizo

    The coordinates of κ-Minkowski spacetime form Lie algebraic elements, in which time and space coordinates do not commute in spite of that space coordinates commute each other. The non-commutativity is realized by a Planck-length-scale constant κ - 1( ne 0), which is a universal constant other than the light velocity under the κ-Poincare transformation. Such a non-commutative structure can be realized by SO(1,4) generators in dS4 spacetime. In this work, we try to construct a κ-Minkowski like spacetime with commutative 4-dimensional spacetime based on Adsn+1 spacetime. Another aim of this work is to study invariant wave equations in this spacetime from the viewpoint of non-local field theory by H. Yukawa, who expected to realize elementary particle theories without divergence according to this viewpoint.

  20. Active Region Filaments Might Harbor Weak Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Díaz Baso, C. J.; Martínez González, M. J.; Asensio Ramos, A.

    2016-05-01

    Recent spectropolarimetric observations of active region filaments have revealed polarization profiles with signatures typical of the strong field Zeeman regime. The conspicuous absence in those observations of scattering polarization and Hanle effect signatures was then pointed out by some authors. This was interpreted as either a signature of mixed “turbulent” field components or as a result of optical thickness. In this article, we present a natural scenario to explain these Zeeman-only spectropolarimetric observations of active region (AR) filaments. We propose a two-component model, one on top of the other. Both components have horizontal fields, with the azimuth difference between them being close to 90°. The component that lies lower in the atmosphere is permeated by a strong field of the order of 600 G, while the upper component has much weaker fields, of the order of 10 G. The ensuing scattering polarization signatures of the individual components have opposite signs, so its combination along the line of sight reduces—and even can cancel out—the Hanle signatures, giving rise to an apparent Zeeman-only profile. This model is also applicable to other chromospheric structures seen in absorption above ARs.