Fast Responding Research Articles

A three-enzyme microelectrode sensor for detecting purine release from central nervous system

As the purines, in particular adenosine, are important signaling agents in the nervous system we have devised a new biosensor for directly measuring their production in real time during physiological activity. Our amperometric adenosine biosensor is made by entrapping 3 enzymes (xanthine oxidase, purine nucleoside phosphorylase and adenosine deaminase) in a composite lactobionamide and amphiphillic polypyrrole matrix around a Pt microelectrode. The resulting sensors are small (25–100 μm diameter), fast responding (10–90% rise time, 2±0.23 s), sensitive (100–222 mA M −1 cm −2) and stable (100% activity after 5 days). The sensor was used in vivo to demonstrate the spatial localization of release of adenosine from Xenopus embryo spinal cord during fictive swimming.

Neural Processing to Visual Stimuli in a Three-Choice Reaction-Time Task

Some authors have suggested that certain components of the event-related potentials (ERPs) reflect underlying stages in the discrimination process. Previous studies have shown that in an auditive three-choice reaction-time task the discrimination is accomplished as a two-stage process, with the more frequently occurring stimulus discriminated at an earlier point than the rarer stimulus and the subjects could be classified as fast and slow responders in function of their response to the most frequent of the three tones. We continuously recorded the electrocerebral activity (EEG) from the scalp and the electromyographic activity (EMG) from the responding muscles in a visual three-choice reaction-time task in 10 strictly right-handed subjects. EEG and EMG responses were subsequently analyzed off-line by aligning them by the onset of either the stimulus (stimulus-synchronized) or the response (response-synchronized). The results suggest that processes of visual stimuli evaluation and response execution are continuously integrated. The discrimination and response systems to visual stimuli is accomplished as a three-stage process, one to frequent tone, another for rare 1, and the last for rare 2. The subjects were classified as fast and slow responders in function of their response to the most frequent of the three tones.

High power continuous wave microwave system at 3.7 GHz

The lower hybrid current drive (LHCD) system is an important system in superconducting steady state tokamak (SST-1). It is used to drive and maintain the plasma current for 1000 s with a duty cycle of 17%. The LHCD system is being designed to launch 1 MW of radio frequency (rf) power at 3.7 GHz. The rf source is comprised of two high power klystron amplifiers, each capable of delivering 500 kW rf power. In this article, the results obtained during installation and commissioning of these klystrons are presented. Two klystrons (model TH2103D) have been successfully installed and commissioned on dummy loads, delivering ∼200 kW power for more than 1000 s. The maximum output power that could be obtained is limited due to the available direct current (dc) power supply. The test system is comprised of a TH2103D klystron, a low power rf (3.7 GHz/25 W) source, two high power four port circulators, two high power dual directional couplers, two arc detector systems, and two dummy water loads. To avoid rf breakdown in the rf components of the transmission line, the system has been pressurized with dry air to 3 bar. To energize and operate the klystron, a high voltage dc power supply, a magnet power supply, an ion pump power supply, a −65 kV floating anode modulator power supply, and a filament power supply are used. An arc detector unit has been installed to detect and initiate action within a few microseconds to protect the klystron, waveguides, and other rf passive components during arcing. To protect the klystron in the event of an arc, a fast responding (<10 μs), rail gap based pressurized crowbar unit has been used. The entire system is water cooled to avoid excess temperature rise during high power continuous wave operation of the klystron and other rf components. The tube requires initial conditioning. Thereafter, the output rf power is studied as a function of beam parameters such as cathode voltage and beam current.

Language-Based Spelling Instruction: Teaching Children to Make Multiple Connections between Spoken and Written Words

Two studies addressed issues related to multiple instructional components in early intervention for at-risk spellers learning to spell polysyllabic words. The first study was a follow-up to a prior second-grade intervention. The fast responders in that study, who were monitored at the beginning and end of third grade ( n=61), maintained their earlier gains during third grade when treatment was withdrawn. Thirty-two of the slower responders received continuing tutoring (12 individual tutorials over 6 to 8 weeks in late fall of third grade), which showed that children who received only alphabet principle training did as well as those who received combined alphabet principle and syllable awareness training (syllable types in English), but that these children required 24 practice trials for short-term mastery of spelling specific words. The second study with a new sample of 48 third graders also evaluated the effectiveness of alphabet principle training only versus combined alphabet principle and syllable awareness training. In these 24 individual tutorials over a 4-month period beginning in the fifth month of third grade, the combined treatment was more effective for (a) spelling untrained transfer words, (b) spelling taught polysyllabic words with a final, silent e syllable, and (c) transfer to phonological awareness. A two-tier model for early intervention to prevent spelling disabilities is proposed. In the first tier alphabet principle is taught (along with other sound-spelling connections for words including syllable awareness) and applied to practice in spelling words singly and in text (teacher-directed dictation and child-generated composition). In the second tier children are monitored in the year following early intervention and continuing tutoring is provided if necessary.

Fast responding biosensor for on-line determination of nitrate/nitrite in activated sludge

A microscale biosensor for nitrate/nitrite was used for in-situ monitoring in an activated sludge plant. The biosensor is based on diffusion of nitrate/nitrite through a tip membrane into a dense mass of bacteria converting the ions into nitrous oxide with subsequent electrochemical detection. The biosensor signal was in very close agreement with the nitrate/nitrite concentration in the plant as analysed by conventional laboratory techniques. The concentration of the only interfering substance, nitrous oxide, was so low that it did not have any effect. The response time of the applied biosensors was less than 30 s, and the detection limit was less than 50 μg N l −1. Detachment of the ion-permeable membrane in the tip of these first-generation biosensors limited the period with continuous monitoring to 5 days.

A New Tool for Eliminating Indoor Air Quality Complaints

Poor indoor air quality (IAQ) can cause a variety of health problems for building occupants including headaches, respiratory problems, eye irritation and fatigue. Traditional IAQ measurements often fail to identify the root cause of the problems and solutions remain elusive. A new IAQ metric, ultrafine particles, is shown to have a high correlation with complaint areas. Researchers are studying the toxicology of these tiny pollutants on animals and humans. Ultrafine particles are defined as particles smaller than 100 nm diameter; ‘nanoparticles’, those smaller than 50 nm diameter, are a subset of ultrafine particles. A battery-powered, portable condensation particle counter (CPC) can be used to quickly identify the source and transport pathways of ultrafine particle contaminants so they can be eliminated or controlled. The CPC condenses isopropyl alcohol on the particles to grow them to an optically detectable size. The hand-held instrument is fast responding, has a wide concentration range, and can log data to detect trends and short-term excursions. Adding the metric of ultrafine particles may become very important to IAQ investigations in the future.

Electrochemical approach to the dynamics of molecular recognition of redox enzyme sites by artificial cosubstrates in solution and in integrated systems.

Application of antigen-antibody technology allows the attachment to an electrode surface of an enzyme monolayer structure to which both the enzyme and the mediator are bound. As illustrated with the example of glucose oxidase and a ferrocene mediator, the enzyme preserves its full activity in such structures, which may be easily reproduced. In spite of their fixation to the structure, the mobility of the ferrocene heads is sufficient to ensure that its transport to the enzyme prosthetic group is not rate determining. The reaction is rather controlled by the prior formation of a complex between the ferrocenium ion and the flavin required for electron transfer to occur. The efficiency of this step is affected by steric hindrance and the various observations made with free-moving and attached ferrocene-ended poly(ethylene glycol) chains may be rationalized by the interplay of factors controlling their distribution and shape. Analyzing the dynamics of this system, in comparison with previous systems, was thus an occasion to shed further light on the recognition phenomenon. The enzyme monolayer integrated system is a good starting point for the step-by-step construction of spatially ordered multilayered assemblies with strong catalytic efficiencies. Fast responding systems are expected both in terms of electron transport and electron transfer between the mediator and the enzyme. The spatial order resulting from the step-by-step construction should allow a much more precise analysis of electron transport and electron transfer than in conventional assemblies of redox centers. Mastering both the construction and the functioning of such systems should help the design of more complex systems, integrating additional functionalities electrically controlled by means of their electron transport/electron transfer connection to the electrode surface.

Light-flecks cause non-uniform stomatal opening – studies with special emphasis on Fagus sylvatica L.

The appearance of stomatal patchiness in response to rapid (seconds) changes in light has been studied in European beech, Fagus sylvatica L., and, by comparison, in a further 17 different woody species from the understorey of a European beech forest, using a simple water infiltration method. Water infiltrated areoles indicate open stomata. Since infiltration changes optical characteristics of a leaf section it can be analysed by photography, computer-aided image analysis and by weighing. For F. sylvatica clear differences were found between infiltration of cotyledons (no patchy pattern) and any other leaf type. Despite identical cultivation, leaves of the same type and age from different individual plants responded differently to application of 30 s of light after darkness. In contrast, the patchiness patterns were very similar for leaves of the same type originating from the same plant. Infiltration patterns after a light-fleck, observed on different leaves as a series of momentary clusters, probably indicate waves of opening stomata moving across the leaf blade. During and after a 30 s light-fleck infiltration increased and it continued to increase in the dark up to 10 min, indicating increasing stomatal opening over that period. In general, shade leaves became more infiltrated (by weight) than half-shade or sun leaves, due to larger intercellular air spaces. All species, without exception, showed patchy infiltration and, thus, non-uniform stomatal opening. Measuring leaf gas exchange (as ”quasi-steady states” using a fast responding system) during photosynthetic induction resulted in very similar CO2 responses of net photosynthesis (A/ci) as in the true steady state, proving that, in shade and half-shade leaves, the presence of stomatal patchiness does not necessarily affect the calculation of intercellular CO2 concentrations. Causes and consequences of stomatal patchiness are discussed.

Central 5-HT depletion enhances impulsive responding without affecting the accuracy of attentional performance: interactions with dopaminergic mechanisms.

A series of ten experiments examined the effects of profound central 5-HT depletion on attentional performance in the rat in the five-choice serial reaction time task, and also determined the effects of such depletion on responding affected by d-amphetamine and by selective dopamine receptor antagonists. Rats were trained to detect and locate brief visual stimuli randomly presented in one of five spatial locations. When performance had stabilised (> 80% correct, < 20% omissions), selective central 5-HT depletion was induced by intracerebroventricular administration of the neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) following pretreatment with both a noradrenergic and a dopaminergic re-uptake inhibitor. The lesioned animals performed the five-choice serial reaction time task with the same degree of accuracy as the sham-operated controls. However, 5-HT depletion reduced the percentage of omitted trials and increased the number of premature/anticipatory responses. This pattern of behaviour following 5-HT depletion could not be attributed to enhanced primary motivation as demonstrated by measures of food intake and latencies to collect food reinforcement. The lesion attenuated the increase of premature responding induced by high doses of systemically administered d-amphetamine. 5-HT depletion also attenuated the dose-dependent decrease in accuracy induced by (-)-sulpiride, a D2 receptor antagonist, although the effects of this drug on response latencies and premature responding were similar in both groups. However, the systemic administration of the D1 receptor antagonist, SCH 23390, blocked the impulsive responding produced by the lesion as indicated by a lack of lesion effects on the percentage of omitted trials and premature responding. The results suggest that central 5-HT depletion results in impulsive, fast responding, which nevertheless does not impair accuracy of visual discrimination performance. The increased impulsivity may be mediated by altered 5-HT-dopamine interactions, with the lesion removing an inhibitory influence over dopamine neurotransmission.

Questionnaire Response Latencies: Implications for Personality Assessment and Self-Schema Theory

We investigated whether the speed of responding to personality questionnaires affects the psychometric quality of the resulting questionnaire scores. Austrian adolescents (n = 106) completed Eysenck's Personality Inventory in a computerized version, which assessed single-item response latencies and the trait levels for neuroticism (N) and extraversion (E). We examined, first, the impact of questionnaire response instructions (speeded versus unspeeded) on test-retest reliability (7 weeks apart) and validity (self-peer agreement). A speeded instruction shortened response latencies, as expected, and made questionnaire scores more reliable (but not more valid). Second, we examined individual differences in habitual response speed. For N, fast responders showed greater validity (but not greater reliability) than slow responders; for E, no such effect was found. We explain these results by means of self-schemata, which appear to moderate the validity of personality assessments, but may do so differently for different traits.

Post-OKT3 induction therapy CD complex response predicts renal allograft rejection.

CD complex response to cessation of induction with OKT3 may be predictive of rejection. Twenty-seven patients receiving renal allografts and OKT3 induction immunosuppression were retrospectively analyzed for CD complex repopulation and allograft rejection. Flow cytometric monitoring was utilized in all patients. Responder status groups were identified based on CD complex repopulation, with fast responders demonstrating CD complex repopulation above the determined cohort mean. Slow responders had repopulation below this mean. Student's t test yielded P<0.01 (CD2), P<0.02 (CD3), and P<0.01 (CD8). Nonresponder patients were identified with repopulation below the mean, but flat compared with depletion. All nine fast responders lost their graft or were treated for rejection. No slow responder experienced graft loss or rejection episodes. One nonresponder was treated for rejection. CD complex activity following OKT3 cessation correlates with future rejection. Identification of responder status provides insight into propensity to reject, allowing individual tailoring of immunosuppression to patient response.

Working-memory load and dimensional complexity of the EEG

This investigation shows that a working-memory load induced by a memory scanning task has an effect on nonlinear descriptors of the EEG dynamics. The effect was locally specific above the fronto-temporal (right) cortex and it may be described as a reduction in the dimensional complexity of cortical brain activity. The meaning of the effects seems to differ from that of EEG spectral power, which varied with time during the experiment and not with changes in the working-memory load conditions. Behaviorally controlled over- and underload led to increased variance of the dimensional complexity, thus indicating that dimensional complexity correlates more closely with actual performance than with more general descriptions of brain states. Habitual response speed had an effect at the parietal lead, thus indicating that fast responders reduced their dimensional complexity as the task demand increased. In contrast, the slower responders showed no such definite trend.

Modified ventilated capsule for the measurement of sweating rate in the exercising horse.

Modification of a ventilated capsule technique for the measurement of sweating rate (SR) is described for application in an exercising horse. The plastic capsule was sealed against the coat of the horse. Dry air was blown through the capsule over the skin and the change in absolute humidity (g/m3) between air entering and leaving the capsule was used to calculate SR. The effect of flow rate on the response characteristics of the system was investigated and measured over a range of sweating rates in a group of horses completing a short exercise test. Repeatability of SR measurements made at 2 sites, one 10 cm distal to the tuber sacrale (SRS) and the other approximately overlying C4 in the neck (SRN), were compared. To encourage the rapid and complete evaporation of moisture from the area of coat enclosed by the SR capsule, it was demonstrated that the degree of saturation of the air leaving the capsule should be maintained below 15% relative humidity (RH). This was best achieved at flow rates exceeding 35 l/min. No significant difference was found between the 2 repeated tests separated by 3 days, with respect to right atrial temperature (TRA) and SR. The modified system for the measurement of SR in the exercising horse used in this study was shown to be fast responding and capable of measuring a wide range of sweating rates. A good seal was maintained throughout and the capsule was removed without causing damage to the coat.

A photo‐cured calcium ion‐selective electrode for use in flow injection potentiometry that tolerates high perchlorate levels

AbstractAn improved photo‐cured membrane selective to calcium was developed based on the calcium bis[4‐(l, 1,3,3‐tetramethylbutyl)phenyl] phosphate ionophore and incorporates the lipophilic additive, potassium tetrakis(p‐chloropheny1)borate. The calcium electrode exhibited a hyper‐Nernstian response of 31.0 mV change per activity decade and a log‐linear range between 1 × 10−5 to 0.1 M in pure calcium chloride solution, in steady‐state mode. The calcium electrode was fast responding, reaching 90% of steady‐state value in 5s making it ideal for flow injection measurements. The photo‐cured electrode can measure calcium in a high perchlorate background, and was used to determine the total calcium level in full cream milk that was digested by a nitric/perchloric acid mixture. The results obtained were in good agreement with atomic absorption spectroscopy measurements.

Optical imaging of brain slice preparations using voltage sensitive dyes

Fast responding, biological membrane-soluble voltage sensitive dyes are probes which make it possible to directly monitor the electrical activity of neuronal tissues with both high temporal and high spatial resolution. High temporal resolution is desirable because of the millisecond time scale on which neuronal events occur. High spatial resolution is desirable to better reveal the complex interactions between different regions of neural circuits.Taking full advantage of the promise of voltage sensitive dyes can be both difficult and expensive. Tissues stained with these dyes undergo very small (often less than one part in a thousand) relative changes in fluorescence in response to changes in transmembrane potential. The signal-to-noise ratio is similarly small for these responses. Finally, the responses are very fast. Most major components of the signal rise to their maximum and then disappear within 15 milliseconds of stimulation (figure 1).Because standard video cameras are inadequate for recording the very small and very fast optical signals transduced by voltage sensitive dyes, specialized detection equipment is required. This entails a high cost per pixel, often limiting the practial number of detector elements to a few hundred or even less.

A fast responding tritium in air monitor for use in operational areas of heavy water power reactors

A fast responding and sensitive tritium-in-air monitor, suitable for monitoring in heavy water-based nuclear power reactors has been described. The detector is a flowcell of 6.3 ml volume, made of stainless steel body and Teflon window and packed with 600 mg of 5 μm thick dry plastic scintillator films. It is coupled to a matched pair of photomultipliers and measurement is made in the coincidence mode of counting. Tritium counting efficiency for direct passage of sample air through the detector is 65%. The sampling rate is 1 to 10 1/min. For an uncontaminated detector, in the absence of any background activity, the instrument records only 2 counts/min as background which is equivalent to the passage of 8000 Bq/m 3 (0.01 DAC) of tritium in air. Microprocessor based electronic compensation has been provided for gaseous radionuclide and gamma background interference. Trial runs of the monitor in our nuclear power plants have shown that the monitor can function on a continuous basis in presence of large levels of gamma background and gaseous radionuclide interference.

Implicating the lexicon: Base-word frequency effects in pseudohomophone naming.

Ss named pseudohomophones (e.g., phocks) and nonpseudohomophones (e.g., snack) under conditions in which words were or were not included in the stimulus lists. For Ss classified as fast responders, pseudohomophone advantages were not accompanied with base-word frequency effects. For slow responders, pseudohomophone naming was related to base-word frequency, but only when words were included in the stimulus lists. A dual-route model is proposed in which (a) lexical representations are frequency sensitive, (b) the relative use of nonlexical vs. lexical information in phonological synthesis depends on strategic factors, and (c) overlapping lexical and nonlexical codes are assumed to lengthen processing time at the level of a phonological buffer

Neural processing in a three-choice reaction-time task: a study using cerebral evoked-potentials and single-trial analysis in normal humans.

1. Previous studies have shown that the long latency event-related potentials (ERPs) reflect certain aspects of the sensory discrimination process, although the coupling of these ERPs to the actual discrimination is variable. Indeed, we have previously shown that during a two-choice reaction time task the discrimination is accomplished as a two-stage process, with the more frequently occurring stimulus discriminated at an earlier point than the rarer stimulus. The present paper examines the hypothesis that, in a three-choice reaction time task, the discrimination is similarly organized, i.e., is accomplished with the use of a three-stage process. 2. In the present experiments, we continuously recorded the electrocerebral activity (EEG) from the scalp and the electromyogram (EMG) from the responding muscles in a three-choice reaction time task in 10 strictly right-handed subjects. EEG and EMG responses were subsequently analyzed off-line by aligning them by the onset of either the stimulus (stimulus-synchronized) or the response (response-synchronized) for both correct and incorrect responses. 3. Subjects could be classified as "fast" or "slow" responders based on the mean response-latency to the most frequently occurring of the three tones (Frequent tone). Fast responders to the Frequent tone were also fast responders to the more frequent of the rare tones (the Rare-1 tone). By contrast, the response latency to the Frequent tone did not predict the speed of response to the most rare tone (the Rare-2 tone). 4. In the response-synchronized averages well-formed premovement potentials were present for the correct responses to all three tones. In the case of the Frequent tone, these potentials were symmetrical over the two cerebral hemispheres (as expected because both hands responded to this tone). They began > or = 200 ms before the average onset of the stimulus, suggesting that the preparation to respond preceded the stimulus. In the case of the two rare tones, the amplitudes of these premovement potentials were asymmetrical over the two hemispheres. For the Rare-1 tone, these potentials were lateralized to the hemisphere contralateral to the hand moved. For the Rare-2 tone, however, these premovement potentials were initially lateralized to the ipsilateral hemisphere, indicating that, even when subjects were able to respond rapidly and correctly to this tone, they were anticipating a need to respond with the incorrect hand (in anticipation of the more frequent Rare-1 tone).(ABSTRACT TRUNCATED AT 400 WORDS)

Involvement of alpha 2-adrenoreceptors and G proteins in the modulation of platelet secretion in response to Streptococcus sanguis.

In the presence of plasma, human platelets secrete the contents of their dense granules and then aggregate in response to certain strains of Streptococcus sanguis. After 2 to 5 min of incubation with streptococci, platelets from fast-responding donors will begin to aggregate. Slow responders aggregate after a longer delay. Platelets may secrete after a short (fast responder) or long (slow responder) delay because of differences in the basal levels or responses to potentiating catecholamines. To test this hypothesis in vitro, endogenous basal catecholamine levels in platelets and plasma from fast and slow responders were analyzed by HPLC with electrochemical detection. The total basal concentration of epinephrine in platelets plus plasma was fourfold higher in fast responders, with the platelet compartment showing the greatest difference. The basal affinity of alpha 2-adrenoreceptors in platelets from both groups was similar when estimated using a specific antagonist, [3H]-yohimbine. Platelets from all donors showed decreased alpha 2-adrenoreceptor affinity in the presence of low (2 nM), but not higher (10 nM), concentrations of added epinephrine. Platelets in the two groups were then compared for secretion of ATP. More ATP was secreted after a shorter delay from fast responding platelets, which was mimicked in slow responders by adding physiologically attainable levels (40 nM) of epinephrine. Addition of the alpha 2-antagonist, phentolamine (10 microM), to the platelets of slow and fast responders completely inhibited or reduced secretion by one third, respectively. Therefore, alpha 2-adrenoreceptors modulate the secretory response of platelets to cells of S. sanguis.(ABSTRACT TRUNCATED AT 250 WORDS)

Linear fast measurement of speed deviation for on-line control of a generating unit physical model

A linear accurate fast responding and simple digital device to measure speed deviation from a reference value, for use in the speed control of the physical model of an electric generating unit, is described in this paper. Such a system requires the measurement of speed deviation with a high degree of resolution over a limited range around the normal speed. The proposed device gives a TTL compatible digital output that is easy to integrate with digital or analogue control systems.