Narrow Spikes Research Articles

Central Control of Dendritic Spikes Shapes the Responses of Purkinje-Like Cells through Spike Timing-Dependent Synaptic Plasticity

Cerebellum-like structures process peripheral sensory information in combination with parallel fiber inputs that convey information about sensory and motor contexts. Activity-dependent changes in the strength of parallel fiber synapses act as an adaptive filter, removing predictable features of the sensory input. In the electrosensory lobe (ELL) of mormyrid fish, a main cellular site for this adaptive processing is the Purkinje-like medium ganglion (MG) cell. MG cells exhibit two types of spikes: narrow axon spikes (N spikes) and broad dendritic spikes (B spikes). N spikes shape ELL output by inhibiting efferent cells, whereas B spikes drive plasticity at parallel fiber synapses. Despite their critical role in plasticity, little is known about the relative importance of various classes of MG cell inputs in driving B spikes or to what extent B spikes can be controlled independently of N spikes. Using in vivo intracellular recordings, measurements of synaptic conductance, and pharmacological blockade of inhibition, we provide evidence for corollary discharge-evoked inhibition that exerts potent control over the timing and probability of B spikes with little apparent effect on N spikes. The timing of this inhibition corresponds to the period during which repeated occurrence of B spikes causes depression of corollary discharge-evoked synaptic responses and a reduction in N spikes. B spikes occurring before or after the period of inhibition lead to increases in corollary discharge-evoked excitation. Thus, by controlling the timing of B spikes, central inhibition shapes the output of MG cells through spike timing-dependent synaptic plasticity. Our findings are consistent with a model of ELL function in which feedback guides adaptive processing by regulating B spikes.

Photometry of particulate surfaces at extremely small phase angles

We present results of goniometric photometry of different samples at extremely small phase angles using a new laboratory setup with a laser light source ( λ=0.63 μm). No opposition effect of carbon soot is found in the range 0.008–1.5°; whereas, MgO deposits and very disperse porous SiO 2 powder demonstrate a narrow brightness spike of significant amplitude. We find a strong dependence of phase curve slope in the range on albedo when studying mixtures of white chalk and carbon soot. These measurements as applied to interpretation of opposition effect observed for Kuiper belt objects suggest that the albedo of these objects cannot be small. Size particle separates of olivine reveal prominent opposition spikes independent of the particle size. Spherical particles with a diameter near 50 μm show significant differences in their scattering behavior depending on whether they form a monolayer or thick particulate surfaces. The latter show a sharp opposition surge unlike the monolayer. Except for the monolayer of spheres, no particulate surface in our measurements yet exhibits phase curve rounding as the phase angle approaches zero.

Dual Z-Source Inverter With Three-Level Reduced Common-Mode Switching

This paper presents the design of a dual Z-source inverter that can be used with either a single dc source or two isolated dc sources. Unlike traditional inverters, the integration of a properly designed Z-source network and semiconductor switches to the proposed dual inverter allows buck-boost power conversion to be performed over a wide modulation range, with three-level output waveforms generated. The connection of an additional transformer to the inverter ac output also allows all generic wye-or delta-connected loads with three-wire or four-wire configuration to be supplied by the inverter. Modulationwise, the dual inverter can be controlled using a carefully designed carrier-based pulsewidth-modulation (PWM) scheme that will always ensure balanced voltage boosting of the Z-source network while simultaneously achieving reduced common-mode switching. Because of the omission of dead-time delays in the dual-inverter PWM scheme, its switched common-mode voltage can be completely eliminated, unlike in traditional inverters, where narrow common-mode spikes are still generated. Under semiconductor failure conditions, the presented PWM schemes can easily be modified to allow the inverter to operate without interruption, and for cases where two isolated sources are used, zero common-mode voltage can still be ensured. These theoretical findings, together with the inverter practicality, have been confirmed in simulations both using PSIM with Matlab/Simulink coupler and experimentally using a laboratory-implemented inverter prototype.

Class I methanol masers in the outflow of IRAS 16 547-4247

The Australia Telescope Compact Array (ATCA) has been used to image class I methanol masers at 9.9, 25 (a series from J = 2 to 9), 84, 95 and 104 GHz located in the vicinity of IRAS 16 547-4247 (G343.12-0.06), a luminous young stellar object known to harbour a radio jet. The detected maser emission consists of a cluster of six spots spread over an area of 30 arcsec. Five spots were detected in only the 84- and 95-GHz transitions (for two spots the 84-GHz detection is marginal), while the sixth spot shows activity in all 12 observed transitions. We report the first interferometric observations of the rare 9.9- and 104-GHz masers. It is shown that the spectra contain a very narrow spike (< 0.03 km s -1) and the brightness temperature in these two transitions exceeds 5.3 × 10 7 and 2.0 × 10 4K, respectively. The three most southern maser spots show a clear association with the shocked gas traced by the H 2 2.12-μm emission associated with the radio jet and their velocities are close to that of the molecular core within which the jet is embedded. This fact supports the idea that the class I masers reside in the interface regions of outflows. Comparison with OH masers and infrared data reveals a potential discrepancy in the expected evolutionary state. The presence of the OH masers usually means that the source is evolved, but the infrared data suggest otherwise. The lack of any class II methanol maser emission at 6.7 GHz in the source raises an additional question, Is this source too young or too old to have a 6.7-GHz maser? We argue that both cases are possible and suggest that the evolutionary stage where the class I masers are active, may last longer and start earlier than when the class II masers are active. However, it is currently not possible to reveal the exact evolutionary status of IRAS 16 547-4247. © 2006 RAS.

Representation of Spatial Goals in Rat Orbitofrontal Cortex

The orbitofrontal cortex (OFC) is thought to participate in making and evaluating goal-directed decisions. In rodents, spatial navigation is a major mode of goal-directed behavior, and anatomical and lesion studies implicate the OFC in spatial processing, but there is little direct evidence for coding of spatial or motor variables. Here, we recorded from ventrolateral and lateral OFC in an odor-cued two-alternative choice task requiring orientation and approach to spatial goal ports. In this context, over half of OFC neurons encoded choice direction or goal port location. A subset of neurons was jointly selective for the trial outcome and port location, information useful for the selection or evaluation of spatial goals. These observations show that the rodent OFC not only encodes information relating to general motivational significance, as shown previously, but also encodes spatiomotor variables needed to define specific behavioral goals and the locomotor actions required to attain them.

Amorphous tracks induced by energetic ions in strongly anisotropic solids with layered structures

Common features of ion-induced tracks in layered structures are analysed in Y‒Ba‒Cu‒O, Bi‒Sr‒Ca‒Cu‒O and in semiconducting GeS and MoS 2. In all crystals, the conduction is poor along the normal layer. The anisotropic electron properties lead to the formation of an ion-induced broad and a narrow thermal spike in these solids. The contribution of the two spikes to the formation of tracks can be separated in GeS. When the gap energy is low or zero (Y‒Ba‒Cu‒O, Bi‒Sr‒Ca‒Cu‒O, MoS 2), only the narrow spike controls the track formation, and the localization of the energy deposition is the same as in insulators. However, the fraction of the deposited energy transferred to the narrow spike is only about one-third of that in insulators. The anisotropic features of tracks show the effect of the energy bands. Good quantitative agreement is found between the experimental data and the predictions of the author’s thermal spike model.

Collaborative detection and filtering of shrew DDoS attacks using spectral analysis

This paper presents a new spectral template-matching approach to countering shrew distributed denial-of-service (DDoS) attacks. These attacks are stealthy, periodic, pulsing, and low-rate in attack volume, very different from the flooding type of attacks. They are launched with high narrow spikes in very low frequency, periodically. Thus, shrew attacks may endanger the victim systems for a long time without being detected. In other words, such attacks may reduce the quality of services unnoticeably. Our defense method calls for collaborative detection and filtering (CDF) of shrew DDoS attacks. We detect shrew attack flows hidden in legitimate TCP/UDP streams by spectral analysis against pre-stored template of average attack spectral characteristics. This novel scheme is suitable for either software or hardware implementation. The CDF scheme is implemented with the NS-2 network simulator using real-life Internet background traffic mixed with attack datasets used by established research groups. Our simulated results show high detection accuracy by merging alerts from cooperative routers. Both theoretical modeling and simulation experimental results are reported here. The experiments achieved up to 95% successful detection of network anomalies along with a low 10% false positive alarms. The scheme cuts off malicious flows containing shrew attacks using a newly developed packet-filtering scheme. Our filtering scheme retained 99% of legitimate TCP flows, compared with only 20% TCP flows retained by using the Drop Tail algorithm. The paper also considers DSP, FPGA, and network processor implementation issues and discusses limitations and further research challenges.

Marine particle nucleation: Observation at Bodega Bay, California

A TSI nano‐SMPS was installed in a lab at Bodega Bay, about 50 m from the coastline and 5 m above sea level. On the basis of measurements conducted from June to December 2001 and from January to June 2003, we have observed two kinds of nucleation events, i.e., long‐term (a few hours) and short‐term (a few minutes) particle bursts. The long‐term events mostly occur during daytime in the summer, lasting from 0.5 to 8 hours. Narrow spikes (short‐term events) that occur year‐round, both day and night, last only a few minutes to a half hour but contain particle number concentrations comparable to some of the long‐term events. Wind direction and speed affect the occurrence and intensity of the particle burst. Nucleation mostly takes place during northwesterly onshore wind for both long‐ and short‐term events, and the probability of nucleation occurrence is higher at higher wind speed. However, in contrast to what has been observed at Mace Head, Ireland, nucleation at Bodega Bay does not correlate with tidal height. Instead, the seasonal and interannual variations of ultrafine particle number concentration N3–10nm appear to correlate with ocean upwelling, a characteristic of currents along the west coast of the United States that brings up nutrients from subsurface waters, promoting plant productivity. Simultaneous measurements of nucleation at the coast and 1.6 km out suggest that nucleation is a coastal phenomenon, supporting the contention that it is related to direct or biogenic emission of precursor gases from the coastal area during the sea upwelling periods.

Ferroelectric domains in nitrobenzene-nitromethane solutions measured by hyper-Rayleigh scattering

Hyper-Rayleigh scattering (HRS) spectra were measured for liquid solutions of C6H5NO2 and CH3NO2 at T=300 K. The depolarized HRS spectra at small frequency shift are dominated by two components due to reorientation of the nitrobenzene molecules. One is a Lorentzian with spectral width nu1=0.16-0.45 cm(-1) and corresponding orientation relaxation time tau=33-12 ps. The second component is a narrow spike with spectral width <2 MHz and corresponding relaxation time tau>80 ns, attributed to HRS from slowly relaxing ferroelectric domains. The dipole order parameter g0=0.053+/-0.005, saturation parameter p=0.9+/-0.1, and volume V=20+/-6 nm3 for these domains in nitromethane were determined from measurements of the nitrobenzene-concentration dependence of the intensity ratio for these two spectral components. Orientation of the 230 nitromethane molecules within each domain is inhomogenous but highly ordered.

Fast electrophoretic analysis of individual mitochondria using microchip capillary electrophoresis with laser induced fluorescence detection

The analysis of mitochondria by capillary electrophoresis usually takes longer than 20 min per replicate which may compromise the quality of the mitochondria due to degradation. In addition, low sample consumption may be beneficial in the analysis of rare or difficult samples. In this report, we demonstrate the ability to analyze individual mitochondrial events in picoliter-volume samples (approximately 80 pL) taken from a bovine liver preparation using microchip capillary electrophoresis with laser-induced fluorescence detection (micro-chip CE-LIF). Using a commercial "double-T" glass microchip, the sample was electrokinetically loaded in the "double-T" intersection and then subjected to electrophoretic separation along the main separation channel. In order to decrease interactions of mitochondria with channel walls during the analysis, poly(vinyl alcohol) was used as a dynamic coating. This procedure eliminates the need for complicated covalent surface modifications within the channels that were previously used in capillary electrophoresis methods. For analysis, mitochondria, isolated from bovine liver tissue, were selectively labelled using 10-nonyl acridine orange (NAO). The results consist of electropherograms where each mitochondrial event is a narrow spike (240 +/- 44 ms). While the spike intensity is representative of its NAO content, its migration time is used to calculate and describe its electrophoretic mobility, which is a property still largely unexplored for intracellular organelles. The five-fold decrease in separation time (4 min for microchip versus 20 min for capillary electrophoresis) makes microchip electrophoretic separations of organelles a faster, sensitive, low-sample volume alternative for the characterization of individual organelle properties and for investigations of subcellular heterogeneity.

A minimal model for decoding of time-limited Ca 2+ oscillations

Calcium oscillations regulate several cellular processes by activating particular proteins. Most theoretical studies focused on the idealized situation of infinitely long oscillations. Here we analyze information transfer by time-limited calcium spike trains. We show that proteins can be selectively activated in a resonance-like manner by time-limited spike trains of different frequencies, while infinitely long oscillations do not show this resonance phenomenon. We found that proteins are activated more specifically by shorter oscillatory signals with narrower spikes.

Temperature of spatially modulated surface of solid film heated by repetitive laser pulses

An analytical solution is obtained for the classical heat conduction problem for a solid film with a surface that is simply deformed and irradiated by repetitive laser pulses. Convective heat losses from the surface and the film–substrate interface are taken into account. The solution, evaluated for large times, shows that the surface deformation increases the average surface temperature. This increase is pronounced when the absorption length of the laser radiation is less than the film thickness (even in the case when the amplitude of surface deformation is much less than its wavelength). At any point on a deformed surface the temporal dependence of temperature is characterized by narrow spikes, which are repeated with the period of pulse repetition. The spatial dependence of surface temperature follows surface deformation.

Characteristic Membrane Potential Trajectories in Primate Sensorimotor Cortex Neurons Recorded In Vivo

We examined the membrane potentials and firing properties of motor cortical neurons recorded intracellularly in awake, behaving primates. Three classes of neuron were distinguished by 1) the width of their spikes, 2) the shape of the afterhyperpolarization (AHP), and 3) the distribution of interspike intervals. Type I neurons had wide spikes, exhibited scoop-shaped AHPs, and fired irregularly. Type II neurons had narrower spikes, showed brief postspike afterdepolarizations before the AHP, and sometimes fired high-frequency doublets. Type III neurons had the narrowest spikes, showed a distinct post-AHP depolarization, or "rebound AHP" (rAHP), lasting nearly 30 ms, and tended to fire at 25-35 Hz. The evidence suggests that an intrinsic rAHP may confer on these neurons a tendency to fire at a preferred frequency governed by the duration of the rAHP and may contribute to a "pacemaking" role in generating cortical oscillations.

Polarization and brightness opposition effects for the E-type Asteroid 64 Angelina

We present new polarimetric and photometric observations of the high-albedo Asteroid 64 Angelina in the UBVRI wavebands at phase angles ranging from 0.43° to 13.02° during oppositions in 1995, 1999, and 2000/2001. The polarization opposition effect has been observed in the form of a sharp peak of negative polarization with amplitude of about −0.4% centered at α min ≈ 1.8 ° , which is superimposed on the regular negative polarization branch. The amplitude of the polarization opposition effect appears to be apparition-dependent. Our photometric data confirm the early detected by Harris et al. [1989. Phase relations of high-albedo asteroids: The unusual opposition brightening of 44 Nysa and 64 Angelina. Icarus 81, 365–374] of a very strong and unusually narrow opposition spike, i.e., brightness opposition effect, for Angelina. Thus, 64 Angelina is the first asteroid for which both the polarization opposition effect and the brightness opposition effect have been detected. We observed that the polarization opposition effect as well as the regular negative polarization branch depends on the wavelength of scattered light, but in different manners. In addition, the colors B–V and V–R show little phase-angle dependence, while the color U–B increases with increasing phase angle, thus indicating that the amplitude of the brightness opposition effect is larger in the U band and almost the same in the B, V, and R bands. It appears that all colors indices begin to increase with decreasing phase angle to zero. The composite lightcurve computed with a period of 8.752 h has amplitude of 0.13 magnitude.

Actinic flux and photolysis in water droplets: Mie calculations and geometrical optics limit

Abstract. Photolysis of water-soluble components inside cloud droplets by ultraviolet/visible radiation may play an important role in atmospheric chemistry. Two earlier studies have suggested that the actinic flux and hence the photolysis frequency within spherical droplets is enhanced relative to that in the surrounding air, but have given different values for this enhancement. Here, we reconcile these discrepancies by noting slight errors in both studies that, when corrected, lead to consistent results. Madronich (1987) examined the geometric (large droplet) limit and concluded that refraction leads to an enhancement factor, averaged over all incident directions, of 1.56. However, the physically relevant quantity is the enhancement of the average actinic flux (rather than the average enhancement factor) which we show here to be 1.26 in the geometric limit. Ruggaber et al. (1997) used Mie theory to derive energy density enhancements slightly larger than 2 for typical droplet sizes, and applied these directly to the calculation of photolysis rates. However, the physically relevant quantity is the actinic flux (rather than the energy density) which is obtained by dividing the energy density by the refractive index of water, 1.33. Thus, the Mie-predicted enhancement for typical cloud droplet sizes is in the range 1.5, only coincidentally in agreement with the value originally given by Madronich. We also investigated the influence of resonances in the actinic flux enhancement. These narrow spikes which are resolved only by very high resolution calculations are orders of magnitude higher than the intermediate values but contribute only little to the actinic flux enhancement when averaged over droplet size distributions. Finally, a table is provided which may be used to obtain the actinic flux enhancement for the photolysis of any dissolved species.

24 Micron Properties of X‐Ray–selected Active Galactic Nuclei

We examine the 24 μm to X-ray color of 157 X-ray-selected active galactic nuclei (AGNs) as a function of X-ray obscuration and optical classification in the Chandra Deep Field-South. The sample consists of the Chandra hard-band detections with 2-8 keV flux above 10-15 ergs s-1 cm-2. A deep 24 μm mosaic obtained with Spitzer provides mid-infrared fluxes for the sample. Since obscured AGNs locally have higher 24 μm/2-8 keV flux ratios than unobscured AGNs, and since X-ray background models predict a large population of obscured AGNs, we expect to find many X-ray-hard, IR-bright AGNs. Instead, we find that the 24 μm to X-ray flux ratio does not depend on X-ray hardness in the full sample, nor does it differ between narrow- and broad-line AGNs. We identify five nearly Compton-thick AGNs and find they have similar 24 μm to X-ray flux ratios compared to the full sample. We consider AGNs in the narrow redshift spikes at z ~ 0.7; for these AGNs, there is some evidence that the flux ratio increases with X-ray hardness. The redshift slice also shows an odd trend that is also prominent in the full sample: a group of X-ray-hard AGNs with very low 24 μm to X-ray flux ratios.

Physiology of Cells in the Central Lobes of the Mormyrid Cerebellum

The cerebellum of mormyrid electric fish is unusual for its size and for the regularity of its histology. The circuitry of the mormyrid cerebellum is also different from that of the mammalian cerebellum in that mormyrid Purkinje cell axons terminate locally within the cortex on efferent cells, and the cellular regions of termination for climbing fibers and parallel fibers are well separated. These and other features suggest that the mormyrid cerebellum may be a useful site for addressing some functional issues regarding cerebellar circuitry. We have therefore begun to examine the physiology of the mormyrid cerebellum by recording intracellularly from morphologically identified Purkinje cells, efferent cells, Golgi cells, and stellate cells in in vitro slices. Mormyrid Purkinje cells respond to parallel fiber input with an AMPA-mediated EPSP that shows paired pulse facilitation and to climbing fiber input with a large all-or-none AMPA-mediated EPSP that shows paired pulse depression. Recordings from the somas of Purkinje cells show three types of spikes in response to injected current: a small, narrow sodium spike; a large, broad sodium spike; and a large broad calcium spike. Efferent cells, Golgi cells, and stellate cells respond to parallel fiber input with an EPSP or EPSP-IPSP sequence and show only large, narrow spikes in response to intracellular current injection. We conclude that the physiology of the mormyrid cerebellum is similar in many ways to the mammalian cerebellum but is also different in ways that may prove instructive concerning the functional circuitry of the cerebellum.

Laboratory Studies of Icy Regoliths in Relation to Observations of Minor Bodies in the Outer Solar System

Observing the properties of solar light scattered by TNOs is (up to now) the only way to obtain information on the physical properties of their surfaces. As such observations, performed near backscattering, become available, it is important to stress the significance of the phase angle and wavelength dependences of the linear polarization of the scattered light. At small phase angles, a narrow spike in brightness and a significantly negative polarization could be typical of icy regoliths, actually expected to be formed by alteration of icy bodies surfaces. Accurate experimental simulations of icy aggregates and regoliths formation that should take place with the ICAPS facility on board the ISS are presented, with emphasis on light scattering measurements providing a link between remote observations of TNOs and physical properties of their surfaces.

LISA data analysis: Doppler demodulation

The orbital motion of the laser interferometer space antenna (LISA) produces amplitude, phase and frequency modulations of a gravitational wave signal. The modulations have the effect of spreading a monochromatic gravitational wave signal across a range of frequencies. The modulations encode useful information about the source location and orientation, but they also have the deleterious effect of spreading a signal across a wide bandwidth, thereby reducing the strength of the signal relative to the instrument noise. We describe a simple method for removing the dominant, Doppler component of the signal modulation. The demodulation reassembles the power from a monochromatic source into a narrow spike and provides a quick way to determine the sky locations and frequencies of the brightest gravitational wave sources.

Modulation of inhibitory autapses and synapses on rat CA1 interneurones by GABA(A) receptor ligands.

To determine whether autaptic inhibition plays a functional role in the adult hippocampus, the action potential afterhyperpolarisations (spike AHPs) of CA1 interneurones were investigated in 25 basket, three bistratified and eight axo-axonic cells. The spike AHPs showed two minima in all regular-spiking (5), burst-firing (3) and in many fast-spiking cells (17:28). The fast component had a time-to-peak (TTP) of 1.2 +/- 0.5 ms, the slower TTP was very variable (range of 3.3-103 ms). The AHP width at half-amplitude (HW) was 12.5 +/- 5.7 ms in fast-spiking, 29.3 +/- 18 ms in regular-spiking and 99.7 +/- 42 ms in burst-firing cells. Axo-axonic cells never establish autapses, and the fast-spiking variety showed narrow (HW: 3.9 +/- 0.7 ms) spike AHPs with only one AHP minimum (TTP: 0.9 +/- 0.1 ms). When challenged with GABA(A) receptor modulators, spike AHPs in basket and bistratified cells were enhanced by zolpidem (HW by 18.4 +/- 6.2 % in 10:15 cells tested), diazepam (45.2 +/- 0.5 %, 6:7), etomidate (43.9 +/- 36 %, 6:8) and pentobarbitone sodium (41 %, 1:1), and were depressed by bicuculline (-41 +/- 5.7 %, 5:8) and picrotoxin (-54 %, 1:1), and the enhancement produced by zolpidem was reduced by flumazenil (-31 +/- 13 %, relative to the AHP HW during exposure to zolpidem, 3:4). Neuronal excitability was modulated in parallel. The spike AHPs of three axo-axonic cells tested showed no sensitivity to etomidate, pentobarbitone or diazepam. Interneurone-to-interneurone inhibitory postsynaptic potentials (IPSPs), studied with dual intracellular recordings, had time courses resembling those of the spike AHPs. The IPSP HW was 13.4 +/- 2.8 ms in fast-spiking (n = 16) and 28.7 +/- 5.8 ms in regular-spiking/burst-firing cells (n = 6), and the benzodiazepine1-selective modulator zolpidem strongly enhanced these IPSPs (45 +/- 28 %, n = 5). Interneurones with spike AHPs affected by the GABA(A) receptor ligands exhibited 3.8 +/- 1.9 close autaptic appositions. In three basket cells studied at the ultrastructural level 6 of 6, 1 of 2 and 1 of 2 close appositions were confirmed as autapses. Therefore, in the hippocampus autaptic connections contribute to spike AHPs in many interneurones. These autapses influence neuronal firing and responses to GABA(A) receptor ligands.