Repeat Trials Research Articles

Analyses of power output of piezoelectric energy-harvesting devices directly connected to a load resistor using a coupled piezoelectric-circuit finite element method

This paper presents, for the first time, a coupled piezoelectric-circuit finite element model (CPC-FEM) to analyze the power output of a vibration-based piezoelectric energy-harvesting device (EHD) when it is connected to a load resistor. Special focus is given to the effect of the load resistor value on the vibrational amplitude of the piezoelectric EHD, and thus on the current, voltage, and power generated by the device, which are normally assumed to be independent of the load resistor value to reduce the complexity of modeling and simulation. The presented CPC-FEM uses a cantilever with a sandwich structure and a seismic mass attached to the tip to study the following characteristics of the EHD as a result of changing the load resistor value: 1) the electric outputs: the current through and voltage across the load resistor; 2) the power dissipated by the load resistor; 3) the displacement amplitude of the tip of the cantilever; and 4) the shift in the resonant frequency of the device. It is found that these characteristics of the EHD have a significant dependence on the load resistor value, rather than being independent of it as is assumed in most literature. The CPC-FEM is capable of predicting the generated output power of the EHD with different load resistor values while simultaneously calculating the effect of the load resistor value on the displacement amplitude of the tip of the cantilever. This makes the CPC-FEM invaluable for validating the performance of a designed EHD before it is fabricated and tested, thereby reducing the recurring costs associated with repeat fabrication and trials. In addition, the proposed CPC-FEM can also be used for producing an optimized design for maximum power output.

Novel Lepidopteran Sex Pheromone Components From <I>Marmara gulosa</I> (Lepidoptera: Gracillariidae)

Marmara gulosa Guillén & Davis (Lepidoptera: Gracillariidae) is a sporadic pest of citrus and a number of other crops in southern and central California. Coupled gas chromatographic-electroantennogram detection analyses of headspace volatiles collected by solid phase microextraction from virgin female moths revealed at least four related compounds in the extracts that elicited significant antennal responses from antennae of male moths. These compounds were identified as (8E,10E)-tetradecadien-1-ol, and the corresponding aldehyde, acetate, and formate ester, representing the first report of a formate as a lepidopteran pheromone component. The four compounds were consistently found in headspace volatiles collected from virgin female moths from different regions of the state and from M. gulosa collected from different host plants (citrus and squash). Repeated field trials determined that the formate ester alone was as attractive or more attractive than any blend of the formate with one or more of the remaining compounds. Although large numbers of moths were caught in some field trials, trap catches were not consistent. Thus, the pheromone may be useful for detection of the moth and setting an initial biofix, but it remains unclear whether the pheromone can be used as a reliable and accurate tool for monitoring densities of M. gulosa populations.

The influence of mental fatigue and motivation on neural network dynamics; an EEG coherence study

The purpose of the present study is to examine the effects of mental fatigue and motivation on neural network dynamics activated during task switching. Mental fatigue was induced by 2 h of continuous performance; after which subjects were motivated by using social comparison and monetary reward as motivating factors to perform well for an additional 20 min. EEG coherence was used as a measure of synchronization of brain activity. Electrodes of interest were identified using a data-driven pre-processing method (ten Caat, M., Lorist, M.M., Bezdan, E., Roerdink, J.B.T.M., Maurits, N.M., 2008a. High-density EEG coherence analysis using functional units applied to mental fatigue. J. Neurosci. Meth. 171, 271–278; ten Caat, M., Maurits, N.M. and Roerdink, J.B.T.M., 2008b. Data-driven visualization and group analysis of multichannel EEG coherence with functional units. IEEE T. Vis. Comp. Gr. 14, 756–771). Performance on repetition trials was faster and more accurate than on switch trials. EEG data revealed more pronounced, frequency specific fronto-parietal network activation in switch trials, while power density was higher in repetition trials. The effects of mental fatigue on power and coherence were widespread, and not limited to specific frequency bands. Moreover, these effects were independent of specific task manipulations. This increase in neuronal activity and stronger synchronization between neural networks did not result in more efficient performance; response speed decreased and the number of errors increased in fatigued subjects. A modulation of the dopamine system is proposed as a common mechanism underlying the observed the fatigue effects.

Maximizing Stone Fragmentation Efficiency With Ultrasonic Probes: Impact of Probe Pressure and Rotation

We examined the effects of probe rotation and pressure on stone fragmentation in an in vitro percutaneous nephrolithotomy model. The study was a fully randomized, factorial experiment with 20 repeat trials performed at each combination of variables, yielding a total of 300 trials per device for ultrasonic tests and 360 for ultrasonic/pneumatic combination tests. Varying masses were placed on the hand piece of each device to create a probe contact pressure of 400, 1,000 or 2,000 gm. The impact of rotation was tested only at 0 or 90 degrees and rotating only at a frequency of 2 Hz. Statistical analysis was performed using R, version 2.6.2. For the Cyberwand the Tukey HSD test showed that 400 and 1,000 gm probe pressure were significantly more effective than 2,000 gm pressure (p <0.05). The range and frequency of rotation were not statistically significant variables affecting Cyberwand efficiency. For the LithoClast Ultra using only the ultrasonic probe significant differences were found among the 3 pressure levels (400, 1,000 and 2,000 gm, respectively, p <0.05). For rotation 90 degrees were significantly more effective than 0 degrees (p <0.05) at a mean +/- SD stone mass of 0.168 +/- 0.078 and 0.107 +/- 0.09 gm, respectively. For the LithoClast Ultra ultrasonic/pneumatic combination 1,000 gm pressure were significantly more effective than 400 or 2,000 gm (p <0.05). The 6 and 12 Hz pneumatic frequencies outperformed 3 Hz but were not significantly different from each other (p <0.05). Differences in probe manipulation impact stone fragmentation efficiency and procedural success.

Functional connectivity patterns during motor behaviour: The impact of past on present activity

Everyday behaviour often depends on the performance of multiple movements executed in a particular order. Here, the impact of task history on the neural activation patterns of motor behaviour is examined by evaluating unimanual and bimanual actions that are produced in a serial arrangement, such that switching between tasks is required. Cortical dynamics was assessed by means of EEG coherence in the beta frequency band (13-30 Hz). Results showed that although behavioural performance was not affected, switching trials induced increased coherence as compared to control (repeat) trials. This reorganization was dependent on task history and was more pronounced for unimanual than for bimanual tasks. Overall, the data illustrate that neural processing of motor behaviour within a serial arrangement integrates past and present activity, and accordingly impacts on neural efficiency.

Distinct Neurophysiological Mechanisms Mediate Mixing Costs and Switch Costs

Using event-related potentials (ERPs), we investigated the neural response associated with preparing to switch from one task to another. We used a cued task-switching paradigm in which the interval between the cue and the imperative stimulus was varied. The difference between response time (RT) to trials on which the task switched and trials on which the task repeated (switch cost) decreased as the interval between cue and target (CTI) was increased, demonstrating that subjects used the CTI to prepare for the forthcoming task. However, the RT on repeated-task trials in blocks during which the task could switch (mixed-task blocks) were never as short as RTs during single-task blocks (mixing cost). This replicates previous research. The ERPs in response to the cue were compared across three conditions: single-task trials, switch trials, and repeat trials. ERP topographic differences were found between single-task trials and mixed-task (switch and repeat) trials at approximately 160 and approximately 310 msec after the cue, indicative of changes in the underlying neural generator configuration as a basis for the mixing cost. In contrast, there were no topographic differences evident between switch and repeat trials during the CTI. Rather, the response of statistically indistinguishable generator configurations was stronger at approximately 310 msec on switch than on repeat trials. By separating differences in ERP topography from differences in response strength, these results suggest that a reappraisal of previous research is appropriate.

Prime retrieval of motor responses in negative priming.

Three auditory identification experiments were designed to specify the prime-response retrieval model of negative priming (S. Mayr & A. Buchner, 2006), which assumes that the prime response is retrieved in ignored repetition trials and interferes with probe responding. In Experiment 1, shortly before (in Experiment 1A) or after (in Experiment 1B) the prime, a cue signaled whether participants were to respond (go trials) or not (no-go trials) to the prime. Negative priming was found in either case. A prime-response retrieval effect-an increase in prime response errors to the probe targets of ignored repetition trials-was found for go trials only. In Experiment 2, prime trials with go cues always demanded a response, whereas the response to no-go trials depended on motor discrimination: For left- (right-) hand responses, the response had to be withheld (valid no-go); for right- (left-) hand responses, the response had to be executed (invalid no-go). The prime-response retrieval effect was present only for go and invalid no-go trials. This implies that execution of the prime response is a precondition for prime-response retrieval, whereas a response preparation plan and a response description in task-specific terms are not sufficient.

Event-related potential correlates of visual identity negative priming unbiased by trial-by-trial effects

Negative priming (NP) refers to slowed reaction times and/or less accurate responses in people responding to a target that was ignored on a previous trial. Although extensive research with behavioral measures has been conducted, little is known about the electrophysiological mechanisms underlying this effect. The few previous studies carried out have led to contradictory results, supporting either episodic-retrieval or inhibition-based theoretical perspectives. In this study, we analyzed the ERP correlates of negative priming by using an experimental global context which, similar to the NP standard context, included Attended repetition trials. In addition, we presented relevant stimuli in separate blocks instead of the more usual randomized design. The NP effect can be biased by strategies adopted by participants when attended and ignored repetition trials are presented randomly. Specifically, we observed an enhanced N2 when a distractor from the previous trial became the target in the next trial. It is supposed that this finding reflects the involvement of additional attentional resources in the selection of a previously inhibited distractor as the new target stimuli.

Role of inhibition in language switching: Evidence from event-related brain potentials in overt picture naming

How are bilinguals able to switch from one language to another? The prevailing inhibition hypothesis takes larger reaction-time (RT) costs for switching to the first language (L1) than to the second language (L2) as evidence for suppression of the non-target language. Switch cost asymmetries can alternatively be explained by an L1-repeat-benefit, assuming selective absence of language competition in repeating L1. To test the latter hypothesis, RTs and event-related brain potentials (ERPs) were recorded when unbalanced Dutch–English bilinguals switched between overt picture naming in L1 and L2. Preparation time (short versus long cue–stimulus intervals) modulated the degree to which top-down inhibitory control biased language competition, as indexed by the N2 component of the ERP. RT switch costs were asymmetrical on short intervals and symmetrical on long intervals. Preparation interval effects were observed in all conditions except for L1 repeat trials. This pattern was present both for RT and N2 data, thereby supporting the L1-repeat-benefit hypothesis. These results suggest that inhibition is not necessary, but can modulate the efficiency of language switching.

No evidence for a late locus of task switch effects

When participants are asked to switch from one task to another, reaction time is longer than in task repetition trials. Current models assume that switch costs are located either at the perceptual stage or at the response selection stage. Contrary to this assumption, Hsieh and Liu ([2005. The nature of switch cost: task set configuration or carry-over effect? Cogn. Brain Res. 22,165–175]) found that task switching affects the response-locked lateralized readiness potential and thus provided evidence for a motor locus of switch costs. We hypothesized that this finding may have been due to methodological artefacts. In order to test this hypothesis, we replicated the experiment by Hsieh and Liu (2005) but avoided some potential methodological artefacts of their study. Our results showed a clear effect of task switching on the stimulus-locked lateralized readiness potential but no effect on the response-locked lateralized readiness potential. Thus, the present study questions the evidence for a late, motor locus of task switch effects but rather indicates a locus at the response selection stage.

ERP indices of persisting and current inhibitory control: A study of saccadic task switching

Previous studies have found that inhibition of a biologically dominant prepotent response tendency is required during the execution of a less familiar, non-prepotent response. However, the lasting impact of this inhibition and the cognitive mechanisms to flexibly switch between prepotent and non-prepotent responses are poorly understood. We examined the neurophysiological (ERP) correlates of switching between prosaccade and antisaccade responses in 22 healthy volunteers. The behavioural data showed significant switch costs in terms of response latency for the prosaccade task only. These costs occurred exclusively in trials when preparation for the switch was limited to 300 ms, suggesting that inhibition of the prepotent prosaccade task either passively dissipated or was actively overcome during the longer 1000 ms preparation interval. In the neurophysiological data, a late frontal negativity (LFN) was visible during preparation for a switch to the prosaccade task that was absent when switching to the antisaccade task, which may reflect the overcoming of persisting inhibition. During task implementation both saccade types were associated with a late parietal positivity (LPP) for switch relative to repetition trials, possibly indicating attentional reorienting to the switched-to task, and visible only with short preparation intervals. When the prosaccade and antisaccade task were contrasted directly during task implementation, the antisaccade task exhibited increased stimulus-locked N2 and decreased P3 amplitudes indicative of active inhibition. The present findings indicate that neurophysiological markers of persisting and current inhibition can be revealed using a prosaccade/antisaccade-switching task.

Sistema de reconocimiento de pruebas clínicas para el registro de productos veterinarios: bases de armonización

The increase of commerce between developing countries requires a harmonised system for accepting the results of clinical trials (CT) of veterinary products, similar to those that exist in developed countries. The objective of this paper is to propose a basis for the creation of a system that harmonises CTs for approving veterinary products (VP) for registration. Such a system would be a step towards unifying the CTs of different countries, while maintaining country-specific variations that are compatible with the scientific method, international standards, and the principles of objectivity, transparency and confidentiality. Basic requirements to be fulfilled by both private institutions and public offices are described, as are professional responsibilities and possible administrative procedures that could be adapted in each country. The conclusion reached is that a harmonised system is feasible, as has been demonstrated in numerous countries throughout the world. A harmonised system will result in a more efficient product approval process, a reduction in costs, greater transparency in controls, an improvement in the reliability of the health system, and a reduction in the time the process takes. It will also contribute to animal welfare by avoiding the need to repeat trials. The author acknowledges that there are cultural, technological and economic limitations and that these problems, and others, have yet to be overcome.

Age, experience and genetic background influence treadmill walking in mice

The use of a treadmill to gather data for gait analysis in mice is a convenient, sensitive method to evaluate motor performance. However, evidence from several species, including mice, shows that treadmill locomotion is a novel task that is not equivalent to over ground locomotion and that may be particularly sensitive to the test environment and protocol. We investigated the effects of age, genetic background and repeated trials on treadmill walking in mice and show that these factors are important considerations in the interpretation of gait data. Specifically we report that as C57BL/6J (B6) mice age, the animals use progressively longer, less frequent strides to maintain the same walking speed. The increase is most rapid between 1 and 6 months of age and is explained, in part, by changes in size and weight. We also extended previous findings showing that repeat trials cause mice to modify their treadmill gait pattern. In a second trial B6 mice consistently walk with a shorter swing phase and greater duty factor. Also, with the shortest retest interval (3 min) mice use shorter more frequent steps but the response varies with the number and timing of trials. Finally, we compared the gait pattern of an additional seven inbred strains of mice and found significant variation in the length and frequency of strides used to maintain the same walking speed. The combined results offer the bases for further mechanistic studies and can be used to guide optimal experimental design.

Short Article: Analysing the relationship between target-to-target and distractor-to-target repetitions: Evidence for a common mechanism

In the present study an assumption of retrieval theories of negative priming was tested. In particular, retrieval theories assume that the same underlying process causes benefits in target-to-target repetition trials and cost effects in distractor-to-target repetition trials in selection tasks in which targets are accompanied by distractor stimuli. More specifically, retrieval theories predict a negative correlation: The higher the benefit in target-to-target repetition trials is, the higher the cost effect in distractor-to-target repetition trials should be. In fact, in a study with considerable power (N = 110) and a design that allowed a confound-free detection of correlations, I observed a significant negative correlation between benefit and cost effects. This result is interpreted as evidence for a common retrieval mechanism.

Diversity and evenness from sequential sightings

Abstract. A method is described for estimating diversity and evenness by observing sequences of sightings of butterflies. Repeat trials in two forest areas produced consistent results and showed a difference between habitats. This is a quick and easy way to assess the pattern in some insect communities, practical when there is little taxonomic expertise.

Experimental gingivitis: reproducibility of plaque accumulation and gingival inflammation parameters in selected populations during a repeat trial

This study aimed to assess whether and to what extent the experimental gingivitis clinical parameters are reproducible within selected populations with different gingival inflammatory response (high or low) to plaque accumulation. In addition, the consistency in developing a high or low gingival inflammatory response within the selected populations was evaluated. Thirty-seven subjects previously identified as high (HR, n=20) or low responders (LR, n=17) during an experimental gingivitis trial (first trial) were enrolled in a "repeat" experimental gingivitis trial. No significant differences in plaque accumulation parameters and bleeding index values were detected between first and repeat trial for the 37 participants. Gingival index was higher during the repeat trial but behaved consistently in terms of the temporal changes in the course of both trials in both populations. Of the 17 LR participants, 10 manifested low susceptibility to inflammation after repeat trial. Among the 20 HR, 10 manifested high susceptibility to inflammation after repeat trial. These results indicate that our experimental gingivitis model is reproducible to some extent in selected populations. The high reproducibility of plaque and, to a lesser extent, of inflammation parameters under the employed controlled conditions could be a valuable tool in gingivitis research.

In vivo estimation and repeatability of force–length relationship and stiffness of the human achilles tendon using phase contrast MRI

To devise a method using velocity encoded phase contrast MRI and MR-compatible dynamometry, for in vivo estimation of elastic properties of the human Achilles tendon and to assess within-session and day-to-day repeatability of this technique. Achilles tendon force and calcaneus-movement-adjusted displacement were measured during a submaximal isometric plantarflexion in 4 healthy subjects, four repeated trials each. The measured force-length (F-L) relationship was least-squares fitted to a cubic polynomial. Typical error was calculated for tendon displacement at multiple force levels, stiffness from the "linear region," and transition point from the displacement point separating the linear and nonlinear parts of the curve. Displacements of the tendon were determined up to a maximum force of 500 N, with mean stiffness of 234 +/- 53 N/mm, mean transition point of 2.70 +/- 0.23 mm and maximum tendon displacement of 3.38 mm. Variability of tendon displacement was not dependent on the force level. Overall typical errors were 0.09 mm and 0.16 mm for within-session and between days, respectively. Typical error of transition point was 0.05 mm and 0.14 mm. Stiffness had typical errors of 47.24 N/mm and 51.95 N/mm. The tendon cross-sectional area and calcaneus displacement were found to be very significant factors in minimizing the individual differences in F-L curves. The method yielded F-L relationships, stiffness, and transition point values that showed good within and day-to-day repeatability. The technique compared well with the more conventional one using ultrasonography. Its reliability indicates potential for measuring tendon structural changes after an injury, disease, and altered loading.

Assessing pedogenic calcite stable-isotope values: Can positive linear covariant trends be used to quantify palaeo-evaporation rates?

Palaeoclimate models suggest enhanced evaporation rates in subtropical regions (15–30° latitude) during greenhouse-world conditions, however, there are no empirical data to support these estimates. Laboratory evaporation experiments have shown that calcites precipitated from variably saturated solutions yield a positive linear covariant trend (PLCT) in δ 18O calcite versus δ 13C calcite values. The goal of the present controlled laboratory experiments is to develop a method to quantify regional palaeo-evaporation rates from palaeosol calcrete PLCTs. Samples of powdered CaCO 3 were dissolved in de-ionized water in pressure sealed containers with a range of elevated atmospheric pCO 2 concentrations for 24 h. The solution was then allowed to evaporate completely from an open container within an incubator with the time of calcite crystallization noted, and aliquots removed for analysis every 24 h. The precipitated calcite produced an array of δ 18O calcite versus δ 13C calcite values that fall upon a PLCT projected from a theoretical meteoric calcite line (MCL). Water analyses yielded δ 18O water enrichments from an initial value of − 4.75‰ VSMOW ranging up to between + 10.0‰ and + 14.8‰. The experimental results show that solutions formed under higher pCO 2 conditions precipitated calcite very early on during evaporation, and thus have δ 18O calcite and δ 13C calcite values that are slightly enriched relative to the MCL. The solutions that formed under low pCO 2 conditions precipitated calcite after much of the fluid had evaporated, and thus yield more enriched δ 18O calcite and δ 13C calcite values. Repeat trials with varying temperature and relative humidity show that the PLCT is steeper under both higher temperature and low relative humidity. The wide range of pCO 2, temperature and relative humidity conditions used simulate meteoric phreatic and meteoric vadose conditions that may affect a calcrete horizon over time during numerous dissolution/precipitation reactions. The results of these experiments show that a dominant factor in the precipitation of vadose calcite is the saturation state of the fluid with respect to CaCO 3, while the primary factors affecting the magnitude and steepness of the PLCT are vadose zone temperature, relative humidity, the starting δ 18O water value and saturation state of the fluid with respect to CaCO 3. Since the pCO 2 of the rooting zone is cross-controlled by the local soil and surface ecology, the magnitude of the PLCT enrichment may not be a direct proxy for palaeo-evaporation rates.

Optical-geometrical characteristics of fragmented figures and integral perception thresholds in repeated tests

The causes of reductions in the integral perception threshold for fragmented figures in repeat trials using the Gollin test were investigated. The first study involved four trials with 5-day intervals using one set of figures. The amplitude-frequency characteristics of the test stimuli were interpreted using correlation analysis, as were the thresholds in each trial. The second study involved two trials with a three-day interval. On repeat testing, half of the figures were known (from the first test) to the subjects. In addition, half of the figures (both familiar and unfamiliar) were fragmented such that their amplitude-frequency characteristics had values similar to those in the first test. The results showed that the decrease in thresholds were mainly due to optimization of the functioning of the mechanisms operating with the statistical rather than the subject characteristics of the images.

Asymmetric switch cost and backward inhibition: Carryover activation and inhibition in switching between tasks of unequal difficulty.

Asymmetric switch cost, observed when switching between tasks varying in difficulty, shows that the difference between repeat and switch trials is greater when switching to the easier task. Early explanations of this effect attributed this pattern to both positive priming of the difficult task and negative priming of the easier task, but more recent models have focused only on activation processes. The role of inhibition in asymmetric switch cost was examined using backward inhibition, a more direct measure of task-set inhibition. The results indicated asymmetric backward inhibition, with greater sequential inhibition of the easier task (i.e., easy-difficult-easy sequences). Switch costs, however, showed both typical and reversed asymmetry (greater cost when switching from the easy to the difficult task), depending on the relative difficulty of task pairs. This pattern of results indicates that switch costs are attributable to both activation and inhibition processes.