Repetitive Rates Research Articles

Development of all-solid-state flash x-ray generator with photoconductive semiconductor switches.

A compact, low-jitter, and high repetitive rate all-solid-state flash x-ray generator making use of photo conductive semiconductor switches was developed recently for the diagnostic purpose of some hydrokinetical experiments. The generator consisted of twelve stages of Blumlein pulse forming networks, and an industrial cold cathode diode was used to generate intense x-ray radiations with photon energy up to 220 keV. Test experiments showed that the generator could produce >1 kA electron beam currents and x-ray pulses with ~40 ns duration under 100 Hz repetitive rates at least (limited by the triggering laser on hand), also found was that the delay time of the cathode explosive emission is crucial to the energy transfer efficiency of the whole system. In addition, factors affecting the diode impedance, how the switching synchronization and diode impedance determining the allowable operation voltage were discussed.

Application of Improved Back Propagation Neural Network in Mowing Robot’s Path Planning

To address the problem of planning complete coverage paths for mowing robots that have the greatest coverage rates and the lowest repetitive rates, we proposed an improved back propagation neural network algorithm based on priority traversal thoughts for local path planning. The algorithm based on plowing global path planning. We adopted grid method to model the environment and used Matlab2010a to simulate for the algorithm. Simulation results show that the proposed algorithm can make the mowing robot walk out of dead zone, the dead zone was composed of obstacle grid or the grid that had been cut around this area, and achieve the complete coverage path planning.

A‐type K+ channels encoded by Kv4.2, Kv4.3 and Kv1.4 differentially regulate intrinsic excitability of cortical pyramidal neurons

Rapidly activating and rapidly inactivating voltage-gated A-type K+ currents, IA, are key determinants of neuronal excitability and several studies suggest a critical role for the Kv4.2 pore-forming α subunit in the generation of IA channels in hippocampal and cortical pyramidal neurons. The experiments here demonstrate that Kv4.2, Kv4.3 and Kv1.4 all contribute to the generation of IA channels in mature cortical pyramidal (CP) neurons and that Kv4.2-, Kv4.3- and Kv1.4-encoded IA channels play distinct roles in regulating the intrinsic excitability and the firing properties of mature CP neurons. In vivo loss of Kv4.2, for example, alters the input resistances, current thresholds for action potential generation and action potential repolarization of mature CP neurons. Elimination of Kv4.3 also prolongs action potential duration, whereas the input resistances and the current thresholds for action potential generation in Kv4.3−/− and WT CP neurons are indistinguishable. In addition, although increased repetitive firing was observed in both Kv4.2−/− and Kv4.3−/− CP neurons, the increases in Kv4.2−/− CP neurons were observed in response to small, but not large, amplitude depolarizing current injections, whereas firing rates were higher in Kv4.3−/− CP neurons only with large amplitude current injections. In vivo loss of Kv1.4, in contrast, had minimal effects on the intrinsic excitability and the firing properties of mature CP neurons. Comparison of the effects of pharmacological blockade of Kv4-encoded currents in Kv1.4−/− and WT CP neurons, however, revealed that Kv1.4-encoded IA channels do contribute to controlling resting membrane potentials, the regulation of current thresholds for action potential generation and repetitive firing rates in mature CP neurons.

Auditory sustained field responses to periodic noise

BackgroundAuditory sustained responses have been recently suggested to reflect neural processing of speech sounds in the auditory cortex. As periodic fluctuations below the pitch range are important for speech perception, it is necessary to investigate how low frequency periodic sounds are processed in the human auditory cortex. Auditory sustained responses have been shown to be sensitive to temporal regularity but the relationship between the amplitudes of auditory evoked sustained responses and the repetitive rates of auditory inputs remains elusive. As the temporal and spectral features of sounds enhance different components of sustained responses, previous studies with click trains and vowel stimuli presented diverging results. In order to investigate the effect of repetition rate on cortical responses, we analyzed the auditory sustained fields evoked by periodic and aperiodic noises using magnetoencephalography.ResultsSustained fields were elicited by white noise and repeating frozen noise stimuli with repetition rates of 5-, 10-, 50-, 200- and 500 Hz. The sustained field amplitudes were significantly larger for all the periodic stimuli than for white noise. Although the sustained field amplitudes showed a rising and falling pattern within the repetition rate range, the response amplitudes to 5 Hz repetition rate were significantly larger than to 500 Hz.ConclusionsThe enhanced sustained field responses to periodic noises show that cortical sensitivity to periodic sounds is maintained for a wide range of repetition rates. Persistence of periodicity sensitivity below the pitch range suggests that in addition to processing the fundamental frequency of voice, sustained field generators can also resolve low frequency temporal modulations in speech envelope.

An optically pumped XeF(C-A) laser with repetitive rate of 10 Hz

A novel XeF(C-A) laser which can be operated in repetition mode has been developed based on surface discharge optical pumping technique. Its maximum repetitive rate is up to 10 Hz. The influence of repetitive rate and gas flow rate on the stability of output energy is studied and the main factor which influences the stability of output energy is analyzed. The experimental results show that increasing the gas flow rate into laser chamber can improve the stability of the output energy. The ideal output energy results of 20 laser pulses under different repetitive rates and their optimal experimental conditions are presented. Output energies of more than 4 J and better stability can be obtained when the laser device operates at 1, 2, and 5 Hz, respectively. When the gas feed rate is larger than 53 l/s, the stability of output energy is improved obviously at the repetitive rate of 10 Hz, and the average energy of 20 laser pulses is up to 3.2 J.

Foot-Tapping Rate as an Objective Outcome Measure for Parkinson Disease Clinical Trials

To explore foot-tapping rate as a reliable and a valid measure of motor function in Parkinson disease (PD). We present data from a randomized, single-blind, outpatient study and a randomized, double-blind, placebo-controlled, crossover, inpatient study. Fifty PD subjects completed the outpatient study. A Unified Parkinson Disease Rating Scale motor score was determined for each subject. Subsequently, finger tapping, alternate (between 2 pedals) and repetitive (on 1 pedal) foot-tapping rates, and gait were measured. Thirteen PD subjects completed the inpatient study. Each subject received a daily infusion of high-dose apomorphine (APO), low-dose APO, and placebo in random order over 3 days. In this subanalysis, we compared variance and reliability of the finger- and the foot-tapping techniques during the placebo day and compared the validity of these outcome measures to detect improvement in parkinsonism during high-dose APO infusion. Alternate foot tapping was reliable (interclass correlation on the placebo inpatient day, 84%). Only foot tapping detected improvement in parkinsonism with high-dose APO treatment (a measure of validity). In the outpatient study, there was a significant correlation between alternate and repetitive tapping with finger tapping (R2 = 0.28 and 0.23, respectively) and Unified Parkinson Disease Rating Scale motor score (R2 = 0.09 and 0.08), but only alternate tapping correlated with gait (R2 = 0.16). Alternate foot tapping was equally reliable but more valid than finger tapping. Alternate foot tapping correlated better did existing PD outcome measures than did repetitive foot tapping. Foot tapping may be a useful outcome measure for determination of dopaminergic medication effect in PD clinical trials.

Differences between familial and sporadic forms of colorectal cancer with DNA microsatellite instability

Microsatellite instability (MSI) is observed in approximately 13% of colorectal cancers. Genes containing a mononucleotide microsatellite in the coding sequence are particularly prone to inactivation in MSI tumourigenesis, and much work has been conducted to identify genes with high repetitive tract mutation rates in these tumours. MSI caused by deficient DNA mismatch-repair functions is a hallmark of cancers associated with the hereditary non-polyposis colorectal cancer syndrome but is also found in about 15% of all sporadic tumours.

Background Mutation Frequency in Microsatellite-Unstable Colorectal Cancer

Microsatellite instability (MSI) is observed in approximately 12% of colorectal cancers. Genes containing a mononucleotide microsatellite in the coding sequence are particularly prone to inactivation in MSI tumorigenesis, and much work has been conducted to identify genes with high repetitive tract mutation rates in these tumors. Much less attention has been paid to background mutation frequencies, and no work has focused on nontranscribed regions. Here, we studied 114 nontranscribed intergenic A/T and C/G repeats 6 to 10 bp in length, located distant from known genes, to examine background mutation frequencies in MSI colorectal cancers. A strong correlation with tract length was observed, and mutation frequencies of up to 87% were observed in 8 to 10 bp tracts. Subsequently, to compare the background mutation rate in transcribed and nontranscribed noncoding repeats, we screened nine randomly selected intronic C/G8 repeats. In addition, the coding repeats of seven suggested MSI target genes, and nine previously published intronic A8 and G8 repeats were analyzed. Intronic repeats seemed to mutate less frequently than nontranscribed intergenic repeats. Our results show that strand slippage mutations in mismatch repair-deficient cells are as abundant in short intergenic repeats as in many proposed MSI target genes. However, under mismatch repair deficiency, strand slippage mutations in transcribed sequences seem to be repaired more efficiently than in intergenic nontranscribed sequences. The mechanisms causing these differences are not yet understood and should be a subject for further studies. For MSI target gene identification, repeats in transcribed sequences seem to be the most appropriate reference group for coding region repeat mutations.

The effect of muscle fatigue on in vivo tibial strains

Stress fracture is a common musculoskeletal problem affecting athletes and soldiers. Repetitive high bone strains and strain rates are considered to be its etiology. The strain level necessary to cause fatigue failure of bone ex vivo is higher than the strains recorded in humans during vigorous physical activity. We hypothesized that during fatiguing exercises, bone strains may increase and reach levels exceeding those measured in the non-fatigued state. To test this hypothesis, we measured in vivo tibial strains, the maximum gastrocnemius isokinetic torque and ground reaction forces in four subjects before and after two fatiguing levels of exercise: a 2 km run and a 30 km desert march. Strains were measured using strain-gauged staples inserted percutaneously in the medial aspect of their mid-tibial diaphysis. There was a decrease in the peak gastrocnemius isokinetic torque of all four subjects’ post-march as compared to pre-run ( p=0.0001), indicating the presence of gastrocnemius muscle fatigue. Tension strains increased 26% post-run ( p=0.002, 95 % confidence interval (CI) and 29% post-march ( p=0.0002, 95% CI) as compared to the pre-run phase. Tension strain rates increased 13% post-run ( p=0.001, 95% CI) and 11% post-march ( p=0.009, 95% CI) and the compression strain rates increased 9% post-run ( p=0.0004, 95% CI) and 17% post-march ( p=0.0001, 95% CI). The fatigue state increases bone strains well above those recorded in rested individuals and may be a major factor in the stress fracture etiology.

Increased Action Potential Firing Rates of Layer 2/3 Pyramidal Cells in the Prefrontal Cortex are Significantly Related to Cognitive Performance in Aged Monkeys

The neurobiological substrates of significant age-related deficits in higher cognitive abilities mediated by the prefrontal cortex (PFC) are unknown. To address this issue, whole-cell current-clamp recordings were used to compare the intrinsic membrane and action potential (AP) firing properties of layer 2/3 pyramidal cells in PFC slices from young and aged behaviorally characterized rhesus monkeys. Most aged subjects demonstrated impaired performance in Delayed Non-Match to Sample (DNMS) task acquisition, DNMS 2 min delay and the Delayed Recognition Span task. Resting membrane potential and membrane time constant did not differ in aged relative to young cells, but input resistance was significantly greater in aged cells. Single APs did not differ in terms of threshold, duration or rise time, but their amplitude and fall time were significantly decreased in aged cells. Repetitive AP firing rates were significantly increased in aged cells. Within the aged group, there was a U-shaped quadratic relationship between firing rate and performance on each behavioral task. Subjects who displayed either low or very high firing rates exhibited poor performance, while those who displayed intermediate firing rates exhibited relatively good performance. These data indicate that an increase in AP firing rate may be responsible, in part, for age-related PFC dysfunction.

Are overground or treadmill runners more likely to sustain tibial stress fracture?

Background: Repetitive high bone strain and/or strain rates, such as those that occur during running, contribute to stress fractures as well as promoting maintenance of or increase in bone mass....

Kv3.4 subunits enhance the repolarizing efficiency of Kv3.1 channels in fast-spiking neurons.

Neurons with the capacity to discharge at high rates--'fast-spiking' (FS) neurons--are critical participants in central motor and sensory circuits. It is widely accepted that K+ channels with Kv3.1 or Kv3.2 subunits underlie fast, delayed-rectifier (DR) currents that endow neurons with this FS ability. Expression of these subunits in heterologous systems, however, yields channels that open at more depolarized potentials than do native Kv3 family channels, suggesting that they differ. One possibility is that native channels incorporate a subunit that modifies gating. Molecular, electrophysiological and pharmacological studies reported here suggest that a splice variant of the Kv3.4 subunit coassembles with Kv3.1 subunits in rat brain FS neurons. Coassembly enhances the spike repolarizing efficiency of the channels, thereby reducing spike duration and enabling higher repetitive spike rates. These results suggest that manipulation of K3.4 subunit expression could be a useful means of controlling the dynamic range of FS neurons.

Ca2+ and K+ currents regulate accommodation and firing frequency in guinea pig bronchial ganglion neurons.

Intracellular microelectrode recordings were obtained from neurons located in adult guinea pig bronchial parasympathetic ganglia in situ to determine the calcium and potassium currents regulating repetitive action potential activity and firing rates by these neurons. Neurons in these ganglia respond to prolonged suprathreshold depolarizing current steps with either a burst of action potentials at the onset of the stimulus (accommodating or phasic neurons) or repetitive action potentials throughout the stimulus (nonaccommodating or tonic neurons). Instantaneous and adapted firing rates during prolonged threshold and suprathreshold stimuli were lower in tonic than in phasic neurons, indicating a longer interspike interval between repetitive action potentials in tonic neurons. In tonic neurons, blockade of A-type current with 4-aminopyridine increased accommodation; 4-aminopyridine or apamin decreased the interspike interval in tonic neurons. Calcium-free buffer, cadmium ions, or omega-conotoxin GVIA also increased accommodation in tonic neurons but did not affect the interspike interval; nifedipine or verapamil did not affect the tonic firing pattern. Accommodation in phasic neurons could be decreased by a conditioning hyperpolarization step of the resting potential, which could be subsequently blocked by 4-aminopyridine or calcium-free buffer. Accommodation in phasic neurons could also be decreased by apamin or barium ions: the repetitive action potentials observed during these treatments could be reversed by cadmium ions or calcium-free buffer. These results indicate that tonic and phasic neurons in guinea pig bronchial parasympathetic ganglia have similar types of calcium currents, but potassium channels may ultimately regulate the accommodation pattern, the firing rate, and, consequently, the output from these neurons.

Repetitive rates of harp seal underwater vocalizations

Underwater recordings of harp seal (Phoca groenlandica) vocalizations, obtained within the breeding herd during March, were examined with respect to calling rate and repetition of calls. Vocalizations typically overlapped one another. Calling rates ranged from 32 to 88 calls/min. Repetition rates averaged between 1.9 and 4.7 sound pulses/call (maximum repetition 24 times). Approximately 30% of the calls were not repeated and 40% were repeated twice. We found no significant relationships between calling rates and repetition rates. There were no variations in these factors throughout the day or month. An automatic level control on the recorder and the overlapping of the calls may have compromised the counts by altering the effective sampling area. The use of vocalization indexes in association with population estimations may be possible only when calls do not overlap.

The laminar organization of optic nerve fibres in the tectum of goldfish.

Potentials in the tectum of large (12--20 cm) goldfish, evoked by stimulation of the optic nerve, were recorded extracellularly with double-barrelled electrodes (d.c., saline and a.c., Woods metal--Pt). Four fibre groups (E, M1, M2, M3) were recorded at latencies of approximately 2, 3, 5 and 8 ms after stimulation (conduction velocities of approximately 7, 5, 3 and 2 m/s). The same four groups were recorded from the optic nerve when the tectum was stimulated. The fastest fibre groups (E) did not give rise to a postsynaptic wave. Fibre groups M1, M2 and M3 gave rise to postsynaptic potentials which, following computation of their second spatial derivatives with depth, were found to have current sinks at depths of approximately 100-150 micrometers, 150--200 micrometers and 250--350 micrometers respectively. Thus the fastest conducting retinotectal fibres make their synapses most superficially, the opposite of the arrangement in the frog tectum. These postsynaptic waves fatigued at repetitive stimulus rates of 20--50 per second, and in twin pulses at interstimulus intervals of 10--15 ms; and they were reversibly blocked by topical application of pentobarbitol. The fibre potentials, however, were virtually undecremented under these conditions. To compare these electrophysiological findings with the anatomy, the cobalt procedure was used to visualize the profiles of the optic fibres in the various tectal laminae. A thick dense projection filled the superficial grey and white (s.g.w.) layer, and there was a thin satellite band just superficial to it. In addition, there were two deeper bands of sparse innervation, in the middle of the central grey zone (c.g.) and in the deep white (d.w.) layer. These bands were associated with the field potential sinks through lesions made with recording electrodes. The two deep bands correspond to the M3 fibre group. The dense s.g.w. innervation contains both the M1 and M2 fibre groups, the M1 just superficial to the M2. The fastest fibre group, E, which had no postsynaptic wave associated with it, persisted at least six weeks after retinal removal, and probably represents efferent cells with fibres projecting back through the optic nerve to the retina. Filled cell profiles could not be positively identified with the cobalt technique, but could be seen with the HRP technique, when the optic afferents were first allowed to degenerate. The filled cells were the pyramidals of the s.g.w. layer.

A variable delay circuit by use at high repetitive rates

A description is given of a circuit suitable for delaying randomly occurring timing signals up to 10 mu s with maximum count rates of some 105 pulses/s. Ordinary coaxial cable has been used as the delay element. The timing error introduced by the circuit under these conditions is smaller than 2 ns. The circuit has been successfully used in performing delayed coincidence experiments in atomic and molecular physics.

Rates of Insemination by Induced Copulation of Aedes vexans (Diptera: Culicidae) Treated with Three Anesthetics1

Laboratory culture of Aedes vexans (Meigen), a floodwater mosquito which fails to mate in cages, is possible only by induced copulation. To induce copulation, females must be immobilized by anesthesia. The influence of anesthetics on rates of insemination was investigated by anesthetizing virgin females with nitrogen, carbon dioxide, and chloroform prior to inducing copulation. Single decapitated males were mated with virgin females for 3 repetitive copulations and rates of insemination were determined by examination of spermathecae. The efficiency of insemination varied according to the anesthetic used for immobilization and by the sequence of mating virgin females with single males. Rates of insemination were consistently high for females anesthetized with nitrogen (87%); intermediate for females anesthetized with carbon dioxide (70%); and low for females anesthetized with chloroform (57%).

Pulse counting and fast scaling transistor circuits

The present state of fast transistor scaling circuits is reviewed and typical designs given for: (1) a frequency divider stage for regular pulses; (2) aperiodic binary circuits for both slow and fast (100 Mc/s p.r.f.) operation; (3) modification of a 4 binary scale-of-16 to a decade scaler operating at 10 Mc/s; (4) general purpose bistable plus AND gates circuits for use in pulse data processing applications as an add and subtract binary scaler or alternatively for gating pulse timingtrains up to 8 Mc/s repetition rates. The present maximum repetitive pulse counting rates of scaler design is about 200 Mc/s but these rates may be exceeded with the use of faster transistors or tunnel diode circuits

Norms for maximum repetitive rates for certain sounds established with the sylrater.

Norms for maximum repetitive rates for certain sounds established with the sylrater.