Slow Signal Research Articles

Thermoluminescence dosimetry properties and kinetic parameters of lithium potassium borate glass co-doped with titanium and magnesium oxides

Lithium potassium borate (LKB) glasses co-doped with TiO2 and MgO were prepared using the melt quenching technique. The glasses were cut into transparent chips and exposed to gamma rays of 60Co to study their thermoluminescence (TL) properties. The TL glow curve of the Ti-doped material featured a single prominent peak at 230°C. Additional incorporation of MgO as a co-activator enhanced the TL intensity threefold. LKB:Ti,Mg is a low-Z material (Zeff=8.89) with slow signal fading. Its radiation sensitivity is 12 times lower that the sensitivity of TLD-100. The dose response is linear at doses up to 103 Gy. The trap parameters, such as the kinetics order, activation energy, and frequency factor, which are related to the glow peak, were determined using TolAnal software.

Optical survey of initial expression of synaptic function in the embryonic chick trigeminal sensory nucleus

We examined the initial expression of synaptic function in the embryonic chick trigeminal nucleus using voltage-sensitive dye recording. Brainstem preparations with three trigeminal nerve afferents, the ophthalmic nerve (N.V1), maxillary nerve (N.V2) and mandibular nerve (N.V3), were dissected from 5.5- to 6.5-day-old chick embryos. In our previous study [Sato et al., 1999], we detected slow signals corresponding to glutamatergic excitatory postsynaptic potentials and identified the principal sensory nucleus of the trigeminal nerve (Pr5), spinal sensory nucleus of the trigeminal nerve (Sp5) and trigeminal motor nucleus. In this study, we examined the effects of removing Mg2+ from the physiological solution, which enhanced N-methyl-d-aspartate receptor function in the sensory nuclei. In 6.5-day-old (St 29) embryos, the slow signal was observed in Pr5 and Sp5 only when N.V1 was stimulated, whereas it appeared in Mg2+-free solution with every nerve stimulation. In 6-day-old (St 28) embryos, the slow signal was observed in Sp5 with N.V1 stimulation, and the appearance of synaptic function in Mg2+-free solution varied, depending on the nerves and preparations used. In 5.5-day-old (St 27) embryos, synaptic function was not detected even when external Mg2+ was removed. These results indicate that the initial expression of synaptic function in the trigeminal system occurs earlier than previously considered, and that the developmental organization of synaptic function differs among the three trigeminal nerves and between the two sensory nuclei.

DOTS: A Propagation Delay-Aware Opportunistic MAC Protocol for Mobile Underwater Networks

Mobile underwater networks with acoustic communications are confronted with several unique challenges such as long propagation delays, high transmission power consumption, and node mobility. In particular, slow signal propagation permits multiple packets to concurrently travel in the underwater channel, which must be exploited to improve the overall throughput. To this end, we propose the delay-aware opportunistic transmission scheduling (DOTS) protocol that uses passively obtained local information (i.e., neighboring nodes' propagation delay map and their expected transmission schedules) to increase the chances of concurrent transmissions while reducing the likelihood of collisions. Our extensive simulation results document that DOTS outperforms existing solutions and provides fair medium access even with node mobility.

Variable timing of synaptic transmission in cerebellar unipolar brush cells

The cerebellum ensures the smooth execution of movements, a task that requires accurate neural signaling on multiple time scales. Computational models of cerebellar timing mechanisms have suggested that temporal information in cerebellum-dependent behavioral tasks is in part computed locally in the cerebellar cortex. These models rely on the local generation of delayed signals spanning hundreds of milliseconds, yet the underlying neural mechanism remains elusive. Here we show that a granular layer interneuron, called the unipolar brush cell, is well suited to represent time intervals in a robust way in the cerebellar cortex. Unipolar brush cells exhibited delayed increases in excitatory synaptic input in response to presynaptic stimulation in mouse cerebellar slices. Depending on the frequency of stimulation, delays extended from zero up to hundreds of milliseconds. Such controllable protraction of delayed currents was the result of an unusual mode of synaptic integration, which was well described by a model of steady-state AMPA receptor activation. This functionality extends the capabilities of the cerebellum for adaptive control of behavior by facilitating appropriate output in a broad temporal window.

Analysis and Priority of Slow Traffic Flow at Signalized Intersection

The slow traffic flow is composed by walking and bike driving. Characteristics of slow traffic flow are fast start and slow speed. The slow traffic and vehicle flow are driving at the same time will cause traffic conflict. The slow traffic priority will be to improve safety and traffic efficiency at the signalized intersection. In this paper, the current problems of slow traffic are analyzed. Combined with the analysis of geometric characteristics of different types of intersection, the principles and implementation conditions of slow traffic priority at the signalized intersection are proposed. From the space priority, the measures of slow traffic priority are proposed at the signalized intersection. From the time priority, slow traffic priority signal timing design flow is proposed.

Evaluation of Slow Light Periodic Signals Considering the Distortion in EDF

Based on the fundamental harmonic phase delay, a new definition of fundamental harmonic fractional delay (FHFD) is proposed to evaluate slow light with the consideration of signal distortion, to eliminate the dependence on the choice of the reference point. By solving the rate equation of erbium-doped fiber (EDF), it is shown that the slow light always accompanies the signal distortion when the periodic signal propagates in EDF, and FHFD depends on the signal distortion, as well as the average input power, the modulation depth and the length of EDF. The results of simulations and experiments indicate that the definition of FHFD is reasonable and effective to evaluate the slow light of periodic signals.

Delay-based congestion control: Flow vs. BitTorrent swarm perspectives

BitTorrent, one of the most widespread file-sharing P2P applications, recently introduced LEDBAT, a novel congestion control protocol aiming at (i) limiting the additional delay due to queuing, to reduce interference with the rest of user traffic (e.g., Web, VoIP and gaming) sharing the same access bottleneck, and (ii) efficiently using the available link capacity, to provide users with good BitTorrent performance at the same time.In this work, we adopt two complementary perspectives: namely, a flow viewpoint to assess the Quality of Service (QoS) as in classic congestion control studies, and a BitTorrent swarm viewpoint to assess peer-to-peer users Quality of Experience (QoE). We additionally point out that congestion control literature is rich of protocols, such as VEGAS, LP, and NICE sharing similarities with LEDBAT, that is therefore mandatory to consider in the analysis. Hence, adopting the above viewpoints we both (i) contrast LEDBAT to the other protocols and (ii) provide deep understanding of the novel protocol and its implication on QoS and QoE.Our simulation based investigation yields several insights. At flow-level, we gather LEDBAT to be lowest priority among all protocols, which follows from its design that strives to explicitly bound the queuing delay at the bottleneck link to a maximum target value. At the same time, we see that this very same protocol parameter can be exploited by adversaries, that can set a higher target to gain an unfair advantage over competitors. Interestingly, swarm-level performance exhibit an opposite trade-off, with smaller targets being more advantageous for QoE of BitTorrent users. This can be explained with the fact that larger delay targets slow down BitTorrent signaling task, with possibly negative effect on the swarming protocol efficiency. Additionally, we see that for the above reason, in heterogeneous swarms, any delay-based protocol (i.e., not only LEDBAT but also VEGAS or NICE) can yield a competitive QoE advantage over loss-based TCP.Overall this tension between swarm and flow-levels suggests that, at least in current ADSL/cable access bottleneck scenarios, a safe LEDBAT operational point may be used in practice. At the same time, our results also point out that benefits similar to LEDBAT can also be gathered with other delay-based protocols such as VEGAS or NICE.

Marking slow light signals with fast optical precursors in the regime of electromagnetically induced transparency

In order to identify special information from a light pulse sequence, we propose a few viable schemes for marking a desired slow light signal with a fast optical precursor in a Λ-type and N-type atomic system. The fast optical precursor is characterized by transient beating patterns originating from the temporal discontinuity of the marking pulse at the sharp rising or falling edge. Compared with the schemes in the Λ system, the one in the N system has the advantage of flexibility in situations in which we are not the sender of the original probe signals. Besides, there is no disturbance to the probe signals nor an undesired main pulse coming from the marking field.

Detection of optical neuronal signals in the visual cortex using continuous wave near-infrared spectroscopy

Near-infrared spectroscopy (NIRS) measures slow hemodynamic signals noninvasively to indirectly infer the neuronal activity in the brain. However, it remains a controversy on whether this optical measurement technique can detect the optical neuronal signal, which reflects the optical changes directly associated with neuronal activity, within the visual cortex of human and non-human primates. By carefully reviewing the important factors in the detection of optical neuronal signals, we aim to investigate the feasibility of performing NIRS measurements of optical neuronal signals within the visual cortex in humans. To ensure a strong optical neuronal response, a full-field circular black and white reversing checkerboard stimulus was presented, and the reversal frequency was carefully chosen. We used a homemade continuous wave (CW) NIRS system with high detection sensitivity (of the order of 0.1pW) to record a large area of the visual cortex (approximately 6×14cm2). EEG was simultaneously acquired with the optical signal. Based on the mathematical morphology, we adapted the filter proposed by Gratton et al. to remove the influence of arterial pulsation and facilitate the detection and elimination of unknown artifacts from the data. We obtained reliable optical neuronal signals in 77% of the participants (10 out of 13). The amplitudes (latencies) of the obtained optical neuronal signals corresponding to the 785 and 850nm wavelengths were 0.017±0.003% (94.7±8.4ms) and 0.025±0.006% (99.0±7.7ms), respectively. There were no significant differences between the latencies of the N75 component of the visual evoked potential (VEP) and optical neuronal signals at either wavelength. This is the first study to report optical neuronal signals within the visual cortex in the intact human brain using a CW NIRS system. These results indicate the feasibility of measuring noninvasive optical neuronal signals using a CW NIRS system with high detection sensitivity.

Mechanisms contributing to cluster formation in the inferior olivary nucleus in brainstem slices from postnatal mice

The inferior olivary nucleus (IO) in in vitro slices from postnatal mice (P5.5-P15.5) spontaneously generates clusters of neurons with synchronous calcium transients, and intracellular recordings from IO neurons suggest that electrical coupling between neighbouring IO neurons may serve as a synchronizing mechanism. Here, we studied the cluster-forming mechanism and find that clusters overlap extensively with an overlap distribution that resembles the distribution for a random overlap model. The average somatodendritic field size of single curly IO neurons was ∼6400 μm(2), which is slightly smaller than the average IO cluster size. Eighty-seven neurons with overlapping dendrites were estimated to be contained in the principal olive mean cluster size, and about six non-overlapping curly IO neurons could be contained within the largest clusters. Clusters could also be induced by iontophoresis with glutamate. Induced clusters were inhibited by tetrodotoxin, carbenoxelone and 18β-glycyrrhetinic acid, suggesting that sodium action potentials and electrical coupling are involved in glutamate-induced cluster formation, which could also be induced by activation of N-methyl-d-aspartate and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors. Spikelets and a small transient depolarizing response were observed during glutamate-induced cluster formation. Calcium transients spread with decreasing velocity during cluster formation, and somatic action potentials and cluster formation are accompanied by large dendritic calcium transients. In conclusion, cluster formation depends on gap junctions, sodium action potentials and spontaneous clusters occur randomly throughout the IO. The relative slow signal spread during cluster formation, combined with a strong dendritic influx of calcium, may signify that active dendritic properties contribute to cluster formation.

Reverse polarity optical-OFDM (RPO-OFDM): dimming compatible OFDM for gigabit VLC links

Visible light communications (VLC) technology permits the exploitation of light-emitting diode (LED) luminaries for simultaneous illumination and broadband wireless communication. Optical orthogonal frequency-division multiplexing (O-OFDM) is a promising modulation technique for VLC systems, in which the real-valued O-OFDM baseband signal is used to modulate the instantaneous power of the optical carrier to achieve gigabit data rates. However, a major design challenge that limits the commercialization of VLC is how to incorporate the industry-preferred pulse-width modulation (PWM) light dimming technique while maintaining a broadband and reliable communication link. In this work, a novel signal format, reverse polarity O-OFDM (RPO-OFDM), is proposed to combine the fast O-OFDM communication signal with the relatively slow PWM dimming signal, where both signals contribute to the effective LED brightness. The advantages of using RPO-OFDM include, (1) the data rate is not limited by the frequency of the PWM signal, (2) the LED dynamic range is fully utilized to minimize the nonlinear distortion of the O-OFDM communication signal, and (3) the bit-error performance is sustained over a large fraction of the luminaire dimming range. In addition, RPO-OFDM offers a practical approach to utilize off-the-shelf LED drivers. We show results of numerical simulations to study the trade-offs between the PWM duty cycle, average electrical O-OFDM signal power, radiated optical flux as well as human perceived light.

Triple decomposition technique in air–water flows: Application to instationary flows on a stepped spillway

Self-sustained instabilities and pseudo-periodic motion may be observed in hydraulic structures and industrial flows. Documented examples include the hydraulic jump, sloshing motion in a reservoir and surging waves in pooled stepped spillways. The instabilities may generate some very large turbulence levels and integral turbulent scales, combining the contributions of both slow fluctuations and fast turbulent fluctuations. Herein a triple decomposition of phase-detection probe signals was developed to identify the turbulent contributions of the slow and fast velocity components in highly aerated free-surface flows. The raw probe signals were split into slow and fast signal components and the air–water flow properties of each component were calculated. The method was applied to a new data set collected down a stepped spillway channel with two stepped configurations (flat and pooled). The latter configuration experienced some self-sustained pseudo-periodic instabilities. The data analysis results showed that the fast turbulent velocity fluctuations of the decomposed signal were close to the turbulence levels on the flat stepped spillway (i.e. in absence of instability). And the largest turbulent energy was contained in the slow fluctuating velocity component. The findings showed a new implementation of a triple decomposition technique to instationary air–water flows.

Tuning Local Calcium Availability: Cell-Type-Specific Immobile Calcium Buffer Capacity in Hippocampal Neurons

It has remained difficult to ascribe a specific functional role to immobile or fixed intracellular calcium buffers in central neurons because the amount of these buffers is unknown. Here, we explicitly isolated the fixed buffer fraction by prolonged whole-cell patch-clamp dialysis and quantified its buffering capacity in murine hippocampal slices using confocal calcium imaging and the "added-buffer" approach. In dentate granule cells, the calcium binding ratio (κ) after complete washout of calbindin D28k (Cb), κfixed, displayed a substantial value of ∼100. In contrast, in CA1 oriens lacunosum moleculare (OLM) interneurons, which do not contain any known calcium-binding protein(s), κfixed amounted to only ∼30. Based on these values, a theoretical analysis of dendritic spread of calcium after local entry showed that fixed buffers, in the absence of mobile species, decrease intracellular calcium mobility 100- and 30-fold in granule cells and OLM cells, respectively, and thereby strongly slow calcium signals. Although the large κfixed alone strongly delays the spread of calcium in granule cells, this value optimizes the benefits of additionally expressing the mobile calcium binding protein Cb. With such high κfixed, Cb effectively increases the propagation velocity to levels seen in OLM cells and, contrary to expectation, does not affect the peak calcium concentration close to the source but sharpens the spatial and temporal calcium gradients. The data suggest that the amount of fixed buffers determines the temporal availability of calcium for calcium-binding partners and plays a pivotal role in setting the repertoire of cellular calcium signaling regimens.

Two-Photon Imaging of Blood Flow in the Rat Cortex

Cerebral blood flow plays a central role in maintaining homeostasis in the brain, and its dysfunction leads to pathological conditions such as stroke. Moreover, understanding the dynamics of blood flow is central to the interpretation of data from imaging modalities--such as intrinsic optical signaling and functional magnetic resonance imaging--that rely on changes in cerebral blood flow and oxygen level to infer changes in the underlying neural activity. Recent advances in imaging techniques have allowed detailed studies of blood flow in vivo at high spatial and temporal resolutions. We discuss techniques to accurately measure cerebral blood flow at the level of individual blood vessels using two-photon laser-scanning microscopy. By directing the scanning laser along a user-defined path, it is possible to measure red blood cell (RBC) velocity and vessel diameter across multiple vessels simultaneously. The combination of these measurements permits accurate assessment of total flux with sufficient time resolution to measure fast modulations in flux, such as those caused by heartbeat, as well as slower signals caused by vasomotion and hemodynamic responses to stimulus. Here, we discuss general techniques for animal preparation and measurement of blood flow with two-photon microscopy. We incorporate extensions to existing methods to accurately acquire flux data simultaneously across multiple vessels in a single trial. Central to these measurements is the ability to generate scan paths that smoothly connect user-defined lines of interest while maintaining high accuracy of the scan path.

Real-time observation of ultrafast internal conversion in ethylbenzene by femtosecond time-resolved photoelectron imaging.

The ultrafast dynamics of the second singlet electronically excited state (S2) in ethylbenzene has been studied by femtosecond time-resolved photoelectron imaging. The time evolution of the photoelectron signal can be well described by a biexponential decay: a rapid relaxation pathway with a time constant of 60 ( ± 9) fs and a longer-lived channel on a timescale of 2.58 ( ± 0.22) ps. The rapid relaxation is ascribed to the ultrafast internal conversion from the S2 state to the vibrationally hot S1 state. This internal conversion process has been observed in real time. The slow photoelectron signal reflects the depopulation of secondarily populated high vibronic S1 state.

Photuris Mysticalampas (Coleoptera: Lampyridae): A New Firefly from Peatland Floodplain Forests of the Delmarva Peninsula

Photuris mysticalampas sp. nov., is described herein. This species can be distin- guished from other Photurids by the combination of its small size, oval body shape, the dense pubes- cent appearance of the elytra, and flash pattern. Adults emerge at night from Sphagnum spp. hum- mocks in acidic peatland floodplain forests and fly slowly among dense understory vegetation at <2m height. Typical flash pattern is a slow signal (0.4 - 0.8 sec) of moderate luminosity for a Photuris repeated at 3 - 7 sec intervals. The species is known only from three sites in two watersheds in Sussex County, Delaware.

Reliable dissipative control of discrete‐time switched singular systems with mixed time delays and stochastic actuator failures

This study is concerned with the problem of reliable dissipative control for a class of discrete-time switched singular systems with mixed time delays and multiple actuator failures. The failure probability of each actuator is individually quantified and is governed by an individual random variable satisfying a certain probabilistic distribution in the interval [0, 1]. Attention is focused on identifying a class of slow switching signals and designing a set of reliable mode-dependent state-feedback controllers such that, for all admissible mixed time delays and multiple probabilistic actuators faults, the closed-loop system is stochastically exponentially admissible and strictly (Q, Q, ℛ)-dissipative. By using the Lyapunov function approach and the average dwell-time scheme, sufficient conditions for the existence of such class of stabilising switching signals and the reliable mode-dependent controllers are derived in terms of linear matrix inequalities, and the explicit expression for the desired controller gains is also given. A numerical example is given to demonstrate the effectiveness of the theoretical results.

Finite-time H∞ control for a class of discrete-time Markovian jump systems with partly unknown time-varying transition probabilities subject to average dwell time switching

An extension of a fixed transition probability (TP) Markovian switching model to combine time-varying TPs has offered another set of useful regime-switching models. This paper is concerned with the problem of finite-time H∞ control for a class of discrete-time Markovian jump systems with partly unknown time-varying TPs subject to average dwell time switching. The so-called time-varying TPs mean that the TPs are varying but invariant within an interval. The variation of the TPs considered here is subject to a class of slow switching signal. Based on selecting the appropriate Lyapunov–Krasovskii functional, sufficient conditions of finite-time boundedness of Markovian jump systems are derived and the system trajectory stays within a prescribed bound. Finally, an example is given to illustrate the efficiency of the proposed method.

Amperometric Resolution of a Prespike Stammer and Evoked Phases of Fast Release from Retinal Bipolar Cells

The neurotransmitter glutamate is used by most neurons in the brain to activate a multitude of different types of glutamate receptors and transporters involved in fast and relatively slower signaling. Synaptic ribbons are large presynaptic structures found in neurons involved in vision, balance, and hearing, which use a large number of glutamate-filled synaptic vesicles to meet their signaling demands. To directly measure synaptic vesicle release events, the ribbon-type presynaptic terminals of goldfish retinal bipolar cells were coaxed to release a false transmitter that could be monitored with amperometry by placing the carbon fiber directly on the larger synaptic terminal. Spontaneous secretion events formed a unimodal charge distribution, but single spike properties were heterogeneous. Larger events rose exponentially without interruption (τ ∼ 30 μs), and smaller events exhibited a stammer in their rising phase that is interpreted as a brief pause in pore dilation, a characteristic commonly associated with large dense core granule fusion pores. These events were entirely Ca(2+)-dependent. Holding the cells at -60 mV halted spontaneous release; and when the voltage was stepped to >-40 mV, secretion ensued. When stepping the voltage to 0 mV, novel kinetic phases of vesicle recruitment were revealed. Approximately 14 vesicles were released per ribbon in two kinetic phases with time constants of 1.5 and 16 ms, which are proposed to represent different primed states within the population of docked vesicles.

Seismic communication in demon African mole rat Tachyoryctes daemon from Tanzania

We describe the production of substrate-borne vibrations in a subterranean mole rat of the genus Tachyoryctes for the first time. These signals with a supposed communication function were recorded using two approaches. Firstly, we recorded the production of spontaneous substrate-borne vibrations of individual test animals in artificial tunnels simulating a mole rat burrow system. Secondly, we recorded substrate-borne vibrations in individuals with interconnected home systems divided by a barrier. We found that Tachyoryctes produces these seismic signals by striking its head against the ceiling of the tunnel. Two types of seismic signals differing in physical parameters were identified. A slow signal (inter-pulse distance 0.12 s, inter-bout distance 3.89 s, number of pulses within each bout 9.53) was produced in both experiments, whereas a fast signal (inter-pulse distance 0.05 s, inter-bout distance 18.44 s, number of pulses within each bout 22.54) was produced mainly in close proximity to another individual. Our results indicate that fast signals are probably individually specific, because the success rate of classification according to discriminant function analysis was 70.4 % for the three tested individuals.