Offset Threshold Research Articles

Assessing uncertainty in genomic offset forecasts from landscape genomic models (and implications for restoration and assisted migration)

IntroductionEcological genomic models are increasingly used to guide climate-conscious restoration and conservation practices in the light of accelerating environmental change. Genomic offsets that quantify the disruption of existing genotype–environment associations under environmental change are a promising model-based tool to inform such measures. With recent advances, potential applications of genomic offset predictions include but are not restricted to: (1) assessing in situ climate risks, (2) mapping future habitat suitability while accounting for local adaptations, or (3) selecting donor populations and recipient areas that maximize genomic diversity and minimize maladaptation to future environments in assisted migration planning. As for any model-based approach, it is crucial to understand how arbitrary decisions made during the modeling process affect predictions and induce uncertainty.MethodsHere, we present a sensitivity analysis of how various modeling components influence forecasts of genomic offset-based metrics, using red spruce (Picea rubens), a cool-temperate tree species endemic to eastern North America, as a case study. We assess the effects of genomic marker set, climatic predictor set, climate change scenario, and “not-to-exceed” offset threshold and evaluate how uncertainty in predictions varies across space.ResultsClimate change scenario induced by far the largest uncertainty to our forecasts; however, the choice of predictor set was also important in regions of the Southern and Central Appalachians that are of high relevance for conservation and restoration efforts. While much effort is often expended in identifying candidate loci, we found that genomic marker set was of minor importance. The choice of a maximum offset threshold to limit transfers between potential donor and recipient locations in assisted migration programs has mostly affected the magnitude rather than geographic variation in our predictions.DiscussionOverall, our model forecasts suggest high climate change risks across the entire distributional range of red spruce and strongly underscore the potential for assisted migration to help ameliorate these risks. In that regard, populations in the Southern and Central Appalachians as well as along the US and Canadian east coast seem the best candidates for both in situ conservation and relocation.

Detection and removal of pacing artifacts prior to automated analysis of 12-lead ECG

BackgroundPacing artifacts must be excluded from the analysis of paced ECG waveform. This study aimed to develop and validate an algorithm to identify and remove the pacing artifacts on ECG and vectorcardiogram (VCG). MethodsWe developed a semi-automatic algorithm that identifies the onset and offset of a pacing artifact based on the VCG signal slope steepness and designed a graphical user interface that permits quality control and fine-tuning the constraining threshold values. We used 1054 ECGs from the retrospective, multicenter cohort study “Global Electrical Heterogeneity and Clinical Outcomes,” including 3825 atrial and 10,031 ventricular pacing artifacts for the algorithm development and 22 ECGs including 108 atrial and 241 ventricular pacing artifacts for validation. Validation was performed per digital sample. We used the kappa-statistic of interrater agreement between manually labeled sample (ground-truth) and automated detection. ResultsThe constraining parameter values were for onset threshold 13.06 ± 6.21 μV/ms, offset threshold 34.77 ± 17.80 μV/ms, and maximum window size 27.23 ± 3.53 ms. The automated algorithm detected a digital sample belonging to pacing artifact with a sensitivity of 74.5% and specificity of 99.6% and classified correctly 98.8% of digital samples (ROC AUC 0.871; 95%CI 0.853–0.878). The kappa-statistic was 0.785, indicating substantial agreement. The agreement was on 98.81% digital samples, significantly (P < 0.00001) larger than the random agreement on 94.43% of digital samples. ConclusionsThe semi-automated algorithm can detect and remove ECG pacing artifacts with high accuracy and provide a user-friendly interface for quality control.

Subglottal pressure oscillations in anechoic and resonant conditions and their influence on excised larynx phonations

Excised larynges serve as natural models for studying behavior of the voice source. Acoustic resonances inside the air-supplying tubes below the larynx (i.e., subglottal space), however, interact with the vibratory behavior of the larynges and obscure their inherent vibration properties. Here, we explore a newly designed anechoic subglottal space which allows removing its acoustic resonances. We performed excised larynx experiments using both anechoic and resonant subglottal spaces in order to analyze and compare, for the very first time, the corresponding subglottal pressures, electroglottographic and radiated acoustic waveforms. In contrast to the resonant conditions, the anechoic subglottal pressure waveforms showed negligible oscillations during the vocal fold contact phase, as expected. When inverted, these waveforms closely matched the inverse filtered radiated sound waveforms. Subglottal resonances modified also the radiated sound pressures (Level 1 interactions). Furthermore, they changed the fundamental frequency (fo) of the vocal fold oscillations and offset phonation threshold pressures (Level 2 interactions), even for subglottal resonance frequencies 4–10 times higher than fo. The obtained data offer the basis for better understanding the inherent vibratory properties of the vocal folds, for studying the impact of structure-acoustic interactions on voice, and for validation of computational models of voice production.

Tracking Error Fitness Function V/F Control of Micro-Grid Based on Genetic Algorithm

This paper presents a method of V/f control parameters tuning for micro-grid based on genetic algorithm. Firstly, the fitness function which representing the tracking error of V/f control system in micro-grid is established. The solving path of genetic algorithm is optimized by using the offset threshold condition between the output voltage and the instruction voltage of the load side, leading to that the individuals with high priority will tend to the optimal solution in the target solution, obtaining the global optimal V/f control parameters. Secondly, the frequency domain response characteristics of equivalent output impedance of V/f control system are analyzed, and the influence of PI parameters on the whole control system is compared. The results shows that the V/f control parameters tuning based on genetic algorithm with the tracking error fitness function can effectively guarantee a constant output of micro-grid’s voltage and frequency. The effectiveness and the advantages of the method is verified by simulation result, which indicated that the proposed method is easy to implement and has a wide range of applications.

Time-optimal selective pulses of two uncoupled spin-1/2 particles

We investigate the time-optimal solution of the selective control of two uncoupled spin 1/2 particles. Using the Pontryagin Maximum Principle, we derive the global time-optimal pulses for two spins with different offsets. We show that the Pontryagin Hamiltonian can be written as a one-dimensional effective Hamiltonian. The optimal fields can be expressed analytically in terms of elliptic integrals. The time-optimal control problem is solved for the selective inversion and excitation processes. A bifurcation in the structure of the control fields occurs for a specific offset threshold. In particular, we show that for small offsets, the optimal solution is the concatenation of regular and singular extremals.

Systolic Peak Detection in Acceleration Photoplethysmograms Measured from Emergency Responders in Tropical Conditions

Photoplethysmogram (PPG) monitoring is not only essential for critically ill patients in hospitals or at home, but also for those undergoing exercise testing. However, processing PPG signals measured after exercise is challenging, especially if the environment is hot and humid. In this paper, we propose a novel algorithm that can detect systolic peaks under challenging conditions, as in the case of emergency responders in tropical conditions. Accurate systolic-peak detection is an important first step for the analysis of heart rate variability. Algorithms based on local maxima-minima, first-derivative, and slope sum are evaluated, and a new algorithm is introduced to improve the detection rate. With 40 healthy subjects, the new algorithm demonstrates the highest overall detection accuracy (99.84% sensitivity, 99.89% positive predictivity). Existing algorithms, such as Billauer's, Li's and Zong's, have comparable although lower accuracy. However, the proposed algorithm presents an advantage for real-time applications by avoiding human intervention in threshold determination. For best performance, we show that a combination of two event-related moving averages with an offset threshold has an advantage in detecting systolic peaks, even in heat-stressed PPG signals.

Muscle activity in cycling: the double burst

The period of a muscle's activity during cycling can be described by the onset and offset of electrical activity. Certain muscles can exhibit two distinct periods of activity (a ‘double...

A lumped mucosal wave model of the vocal folds revisited: Recent extensions and oscillation hysteresis

This paper examines an updated version of a lumped mucosal wave model of the vocal fold oscillation during phonation. Threshold values of the subglottal pressure and the mean (DC) glottal airflow for the oscillation onset are determined. Depending on the nonlinear characteristics of the model, an oscillation hysteresis phenomenon may occur, with different values for the oscillation onset and offset threshold. The threshold values depend on the oscillation frequency, but the occurrence of the hysteresis is independent of it. The results are tested against pressure data collected from a mechanical replica of the vocal folds, and oral airflow data collected from speakers producing intervocalic /h/. In the human speech data, observed differences between voice onset and offset may be attributed to variations in voice pitch, with a very small or inexistent hysteresis phenomenon.

The Carbon Neutral Public Sector

This paper argues for research into the effectiveness of government strategies for a ‘carbon neutral public sector’. We review initiatives in three OECD countries: New Zealand, Australia and the UK. In all jurisdictions, government agencies have consistently stressed ‘leading by example’ as a rationale for adoption. ‘Direct mandate’ by the Prime Minister (NZ); ‘organic development’ from wider central government sustainability initiatives (UK); and a more ‘laissez faire’ approach by Australian Federal and State Governments, were identified as the general pathways leading to implementation. Our assessment indicates: a lack of understanding of the implementation process for carbon neutrality; a need to identify and critically examine the ‘offset threshold’ at which mitigation efforts cease and offsetting is adopted; an absence of any evaluation of the ‘leading by example’ rationale; a lack of inter-country comparisons; a gap in understanding the relationship with economic and social aspects of sustainability; and a need to evaluate the utility of core government departments as the focus of carbon accounting. We urge colleagues to consider research in this area with a view to contributing to the interdisciplinary solutions which we believe are required.

SU‐GG‐J‐73: Dose Distribution Improvements for Prostate Cancer Patients Using Hybrid Image Guidance Systems

Purpose: Daily setup variations may compromise the precision of dose delivery, tumor control and normal tissue avoidance. This study analyzed the setup variations predicted by kilo‐voltage Cone Beam CT (CBCT) combined with 3D Ultrasound image guidance. The overall integrity of prostate dose distribution was considered to define an offset threshold above which image guidance becomes crucial for dose delivery. Method and Materials: Initial immobilization was performed using three‐point in‐room lasers. The residual positional errors were assessed using CBCT from Varian Trilogy™ and Ultrasound guidance by Sonarray™ system. Superposition of offset vectors on the initial prostate plans enabled detailed evaluation of resultant changes in dosimetric and biological aspects for target and organs at risk. On‐line CBCT images were used for calculation. Dose volume histograms (DVH), Gamma Index (GI), equivalent uniform dose (EUD) and tumor control probability (TCP) were calculated. Other indices such as mean total dose (mTd) and maximal total dose (MTD) for normal structures were also considered in defining the threshold. Results and Conclusion: After initial laser alignment, the mean vector of residual displacements over all prostate patients is 6.2mm with a 5.0mm standard deviation. The decrease in EUD for defined tumor volumes was up to 66% when the largest offset was applied and 10% in the composite plan which incorporated overall offset histories. Results show that if patient's offsets were smaller than the applied PTV margin (5mm), unappreciable changes in dose coverage and tumor control were revealed. However, if offsets were larger than the PTV margin, tumor control and normal tissue sparing can be significantly compromised if proper couch shifts are not made under the imaging guidance system. In this situation, special attention is needed especially on organs at risk and even the adaptive radiotherapy might be necessary.

Mechanical experimental setup to simulate vocal folds vibrations: preliminary results

This paper contributes to the understanding of vocal folds oscillation during phonation. In order to test theoretical models of phonation, a new experimental set-up using a deformable vocal folds replica is presented. The replica is shown to be able to produce self sustained oscillations under controlled experimental conditions. Therefore different parameters, such as those related to elasticity, to acoustical coupling or to the subglottal pressure can be quantitatively studied. In this work we focused on the oscillation fundamental frequency and the upstream pressure in order to start (on-set threshold) either end (off-set threshold) oscillations in presence of a downstream acoustical resonator. As an example, it is shown how this data can be used in order to test the theoretical predictions of a simple one-mass model.&#x0D;

Cross-sectional analysis of hearing threshold in relation to age in a large family with cochleovestibular impairment thoroughly genotyped for DFNA9/COCH.

Hearing threshold was analyzed for each frequency in relation to age in 88 members of a large Dutch family with cochleovestibular impairment caused by a P51S mutation in the COCH gene within the DFNA9 locus (chromosome 14q12-13). The participants in this study were 34 mutation carriers and 54 relatives without the mutation (control subjects). A sigmoidal dose-response curve with a variable slope was used to fit the mutation carriers' threshold-on-age data. Progression started at about 40 years of age and only lasted for some 20 to 25 years; the associated average progression was 2.9 dB/y for all frequencies. However, some hearing impairment was already present before, predominantly at the high frequencies. The mean thresholds in the young mutation carriers (< 33 years of age) were significantly higher (by 4 to 13 dB) than those in age-matched controls at 2 to 8 kHz. Presumably, mutation carriers have a congenital, stable offset threshold (10 to 29 dB) at these frequencies, and develop progression later in life.

Nonsyndromic autosomal dominant progressive sensorineural hearing loss: audiologic analysis of a pedigree linked to DFNA2.

An analysis was performed of the regression of the individual hearing threshold on age in the affected persons in a six-generation Dutch family with nonsyndromic autosomal dominant sensorineural hearing loss, which showed linkage to the DFNA2(1p34) region, similar to at least four previously reported nonrelated families. The offset threshold was significantly higher at the high frequencies (around 30 dB at 2 to 8 kHz) than at the lower ones (approximately 0 dB at 0.25 to 1 kHz). Hearing impairment at the higher frequencies may therefore have been present already at birth or in early childhood. The regression coefficient, or the 'annual threshold increase,' expressed in dB/y, was about 1 dB/y on average, but the higher frequencies (1 to 8 kHz) showed significantly more rapid progression than the lower frequencies (0.25 to 0.5 kHz).

Further studies of phonation threshold pressure in a physical model of the vocal fold mucosa.

This paper reports results of further experimentation on a previously developed physical model of the vocal-fold mucosa [Titze et al., J. Acoust. Soc. Am. 97, 3080-3084 (1995)]. The effects of vocal-fold thickness, epithelial membrane thickness, and prephonatory glottal geometry on phonation threshold pressure were studied. Phonation threshold pressures in the range of 0.13 to 0.34 kPa were observed for an 11-mm-thick vocal fold with a 70-micron-thick "epithelial" membrane for different "mucosal" fluid viscosities. Higher threshold pressure was always obtained for thinner vocal folds and thicker membranes. In another set of experiments, lowest offset threshold pressure was obtained for a rectangular or a near-rectangular prephonatory glottis (with a glottal convergence angle within about +/- 3 degrees). It ranged from 0.07 to 0.23 kPa for different glottal half-widths between 2.0 and 6.0 mm. The threshold for more convergent or divergent glottal geometries was consistently higher. This finding only partially agrees with previous analytical work which predicts a lowest threshold for a divergent glottis. The discrepancy between theory and data is likely to be associated with flow separation from a divergent glottis.

EUROMAC. A European concerted action: maternal alcohol consumption and its relation to the outcome of pregnancy and child development at 18 months. Results--strategy of analysis and analysis of pregnancy outcome.

Analyses were made of the relation between maternal alcohol consumption before and in early pregnancy and five infant outcome variables: birthweight, crown-heel length, occipitofrontal circumference and the Apgar scores at 1 and 5 minutes. The data were analysed for all centres combined and separately. From tabulation of the mean values of the outcome variables by alcohol consumption, it appeared that a poorer outcome was related to consumption of 120 g/week absolute alcohol or more. Multiple regression analysis was used to allow for possible confounding by the child's gestational age at birth and sex, the mother's age, parity and smoking habit, and survey centre. Two threshold models were applied to the combined data, taking the confounders into account. The offset threshold model (assuming no effect of alcohol up to a threshold value, and then a constant multiplicative effect at higher levels) suggested a negative effect on birthweight at about 60 g/week absolute alcohol, but with a wide 85% confidence interval of 5-130 g/week. A step function threshold model, which assumes a constant effect above the threshold value, behaved erratically. Similar analyses for crown-heel length and occipitofrontal circumference provided only a very poor fit to the data. Data on reported congenital anomalies are presented by survey centre and maternal alcohol consumption, but due to the unstandardized method of collection they were not analysed further.

Position sense of the peripheral retina.

Position acuity was measured over a wide range of eccentricities, from 3 min to 10 deg in the horizontal meridian, by using both a three-dot bisection task and a three-dot vernier task. A foveal fixation dot appeared for 1 sec before an outer pair of test dots was flashed for 200 msec. Bisection and vernier tasks were used to measure position acuity in the radial and tangential directions, respectively. The vernier data were well fitted by a straight line on linear axes of offset threshold versus eccentricity. The bisection data, on the other hand, were poorly fitted by a single straight line. However, a double-line fit worked very well. The line segment at large eccentricities (greater than 0.5 deg) had an x intercept of about 0.6 deg, in good agreement with previous estimates based on cortical magnification and on hyperacuity in the presence of flanks. These results imply that three-dot vernier thresholds are set by a single orientation mechanism at all eccentricities and that three-dot bisection thresholds are set by a pair of mechanisms. For eccentricities less than 15 min, thresholds are in good agreement with calculations based on spatial-frequency filters. For larger eccentricities, the bisection thresholds agree with scaled anatomical modules that are presumed to exist in the human visual cortex. The thresholds for position acuity in the tangential direction are as low as 0.005 times the eccentricity. In the radial direction, thresholds are poorer, implying that additional cortical factors may further constrain performance.

Areas of spatial interaction for a hyperacuity stimulus

We report that the ability to detect a small vernier offset (less than 5 sec of arc in many individuals) between two small spots of light separated by a narrow gap can be disrupted by presenting additional targets in close proximity to the vernier stimulus. A rectangular background of light, centered on the vernier stimulus, elevates offset threshold by a factor of two when the total width of the background is 3–4 min arc. Backgrounds narrower or wider than 3–4 min have less or no effect on vernier threshold. These areas of spatial interaction extend to either side of a vertically-oriented vernier stimulus, or above and below a horizontally-oriented stimulus, and their extent is dependent upon the gap size of the two-dot stimulus. The effect of the presence of the background on vernier threshold cannot be accounted for by spatial interval cues nor by changes in the visibility of the stimulus. Two alternative interpretations of the results are presented to develop a description of the underlying mechanisms which produce hyperacuity spatial interactions.

Vernier acuity predicted from changes in the light distribution of the retinal image.

If two thin bars of different luminance are placed side by side, their joint spatial position in a Vernier alignment task is determined simply by their relative luminances. The threshold luminance contrast difference required to produce a just detectable change in spatial position corresponds to a spatial shift of 5-20 arcsec in the centroid of the retinal light distribution, depending upon contrast relative to the background. This technique may be used to measure acuity with a display that has a spatial resolution considerably worse than the Vernier offset threshold. We have also extended the centroid technique to components that differ both in wavelength and luminance. Colour was found to make no essential difference to the task. Taking into account the spread of light in the retinal image, the manifest contrast thresholds are equivalent to threshold intensity increments between adjacent foveal receptors of less than 1% comparable to the values reported by Hecht and Mintz for dark line detection.

Intracortical processing of visual contour information in cats.

Fine slices made through the gray matter perpendicular to the surface of cortical area 17-18 in the cat produced no change in behavioral measures of grating acuity, a modest reduction in vernier acuity and a proportionately larger effect on contour orientation acuity. The introduction of vertical gaps in the vernier acuity targets produced increases in the vernier offset threshold proportional to the gap size both before and after cortical damage, except at the largest vertical gap values employed (1-1.5 degrees) where no change in thresholds was observed after surgery. Neither the preoperative vernier thresholds nor the postoperative changes in vernier thresholds were predicted by the measured contour orientation thresholds and thus an orientation discrimination model of vernier acuity was not supported. The results of this study support the view that intracortical processing in area 17-18 is important in both vernier and orientation acuity, but the neural mechanisms mediating the two capacities are different.

Selection Diversity Combiner Design for Digital LOS Radios

The use of an offset threshold performance monitor to control selection diversity combining in a digital Line-of-Sight (LOS) radio is explored. A novel hybrid computer simulation is used to synthesize dual independently fading channels, diversity radio receivers, digital performance monitors and a selection diversity switch. Based on simulations and a theoretical analysis, design relationships for various performance monitor and diversity switch parameters are defined. The optimization of these parameters, such as the response bandwidth of the performance monitor and the switch hysteresis, will maximize the diversity improvement obtainable in a selection diversity system. Finally, a diversity switch algorithm is proposed which integrates outputs from offset threshold and diversity receiver Automatic Gain Control (AGC) monitors to assure effective diversity operation under realistic fading conditions.