Hz Sampling Rate Research Articles

Pathologic substrates of focal epilepsy influence the generation of high‐frequency oscillations

Although a clear correlation has been observed between high-frequency oscillations (HFOs) and the seizure-onset zone in distinct lesions, the role of the underlying pathologic substrates in the generation of HFOs is not well established. We aimed to investigate HFO correlates of different pathologic substrates in patients with drug-resistant epilepsy, and to examine the relation of HFOs with the anatomic location of the dysplastic lesion and surrounding tissue in patients with focal cortical dysplasia (FCD). We studied consecutive patients with drug-resistant epilepsy who underwent intracranial electroencephalography (iEEG) investigations with depth electrodes at the Montreal Neurological Institute and Hospital, between November 2004 and May 2013. Inclusion criteria were the following: a focal lesion documented by magnetic resonance imaging (MRI); EEG recording at a 2,000 Hz sampling rate; and seizures starting from depth electrode contacts placed in lesion and perilesional tissue. Thirty-seven patients (13 FCD, 12 mesial temporal sclerosis, five cortical atrophy, three polymicrogyria, three nodular heterotopia, and one tuberous sclerosis) were included; 18 were women (median age 34). Ripples and fast ripples were found in all lesion types, except tuberous sclerosis, which showed no fast ripples. There was a significant difference in rates of ripples and fast ripples across different lesions (p < 0.001), with higher rates in FCD, mesial temporal sclerosis, and nodular heterotopia than in atrophy, polymicrogyria, and tuberous sclerosis. Regarding patients with FCD, HFOs rates differed significantly across the three types of tissue (lesional, perilesional, and nonlesional; p < 0.001), being higher within the borders of the MRI-visible dysplastic lesion, followed by the surrounding area, and rare in the remote cortex. Our findings suggest that in patients who are all intractable, the HFO rates vary with different pathologies, and reflect different types of neuronal derangements. Our results also emphasize the potential usefulness of HFOs as an additional method to better define the extent of the epileptogenic dysplastic tissue in FCD.

Monitoring local heating around an interventional MRI antenna with RF radiometry.

Radiofrequency (RF) radiometry uses thermal noise detected by an antenna to measure the temperature of objects independent of medical imaging technologies such as magnetic resonance imaging (MRI). Here, an active interventional MRI antenna can be deployed as a RF radiometer to measure local heating, as a possible new method of monitoring device safety and thermal therapy. A 128 MHz radiometer receiver was fabricated to measure the RF noise voltage from an interventional 3 T MRI loopless antenna and calibrated for temperature in a uniformly heated bioanalogous gel phantom. Local heating (ΔT) was induced using the antenna for RF transmission and measured by RF radiometry, fiber-optic thermal sensors, and MRI thermometry. The spatial thermal sensitivity of the antenna radiometer was numerically computed using a method-of-moment electric field analyses. The gel's thermal conductivity was measured by MRI thermometry, and the localized time-dependent ΔT distribution computed from the bioheat transfer equation and compared with radiometry measurements. A "H-factor" relating the 1 g-averaged ΔT to the radiometric temperature was introduced to estimate peak temperature rise in the antenna's sensitive region. The loopless antenna radiometer linearly tracked temperature inside a thermally equilibrated phantom up to 73 °C to within ±0.3 °C at a 2 Hz sample rate. Computed and MRI thermometric measures of peak ΔT agreed within 13%. The peak 1 g-average temperature was H = 1.36 ± 0.02 times higher than the radiometric temperature for any media with a thermal conductivity of 0.15-0.50 (W/m)/K, indicating that the radiometer can measure peak 1 g-averaged ΔT in physiologically relevant tissue within ±0.4 °C. Active internal MRI detectors can serve as RF radiometers at the MRI frequency to provide accurate independent measures of local and peak temperature without the artifacts that can accompany MRI thermometry or the extra space needed to accommodate alternative thermal transducers. A RF radiometer could be integrated in a MRI scanner to permit "self-monitoring" for assuring device safety and/or monitoring delivery of thermal therapy.

Distributed strain measurement based on long-gauge FBG and delayed transmission/reflection ratiometric reflectometry for dynamic structural deformation monitoring.

In this paper, we propose a delayed transmission/reflection ratiometric reflectometry (DTR(3)) scheme using a long-gauge fiber Bragg grating (FBG), which can be used for dynamic structural deformation monitoring of structures of between a few to tens of meters in length, such as airplane wings and helicopter blades. FBG sensors used for multipoint sensing generally employ wavelength division multiplexing techniques utilizing several Bragg central wavelengths; by contrast, the DTR(3) interrogator uses a continuous pulse array based on a pseudorandom number code and a long-gauge FBG utilizing a single Bragg wavelength and composed of simple hardware devices. The DTR(3) scheme can detect distributed strain at a 50 cm spatial resolution using a long-gauge FBG with a 100 Hz sampling rate. We evaluated the strain sensing characteristics of the long-gauge FBG when attached to a 2.5 m aluminum bar and a 5.5 m helicopter blade model, determining these structure natural frequencies in free vibration tests and their distributed strain characteristics in static tests.

Characterisation of nanoparticle emissions and exposure at traffic intersections through fast–response mobile and sequential measurements

Quantification of disproportionate contribution made by signalised traffic intersections (TIs) to overall daily commuting exposure is important but barely known. We carried out mobile measurements in a car for size–resolved particle number concentrations (PNCs) in the 5–560 nm range under five different ventilation settings on a 6 km long busy round route with 10 TIs. These ventilation settings were windows fully open and both outdoor air intake from fan and heating off (Set1), windows closed, fan 25% on and heating 50% on (Set2), windows closed, fan 100% on and heating off (Set3), windows closed, fan off and heating 100% on (Set4), and windows closed, fan and heating off (Set5). Measurements were taken sequentially inside and outside the car cabin at 10 Hz sampling rate using a solenoid switching system in conjunction with a fast response differential mobility spectrometer (DMS50). The objectives were to: (i) identify traffic conditions under which TIs becomes hot–spots of PNCs, (ii) assess the effect of ventilation settings in free–flow and delay conditions (waiting time at a TI when traffic signal is red) on in–cabin PNCs with respect to on–road PNCs at TIs, (iii) deriving the relationship between the PNCs and change in driving speed during delay time at the TIs, and (iv) quantify the contribution of exposure at TIs with respect to overall commuting exposure. Congested TIs were found to become hot–spots when vehicle accelerate from idling conditions. In–cabin peak PNCs followed similar temporal trend as for on–road peak PNCs. Reduction in in–cabin PNC with respect to outside PNC was highest (70%) during free–flow traffic conditions when both fan drawing outdoor air into the cabin and heating was switched off. Such a reduction in in–cabin PNCs at TIs was highest (88%) with respect to outside PNC during delay conditions when fan was drawing outside air at 25% on and heating was 50% on settings. PNCs and change in driving speed showed an exponential–fit relationship during the delay events at TIs. Short–term exposure for ∼2% of total commuting time in car corresponded to ∼25% of total respiratory doses. This study highlights a need for more studies covering diverse traffic and geographical conditions in urban environments so that the disparate contribution of exposure at TIs can be quantified.

Intercomparison of fast response commercial gas analysers for nitrous oxide flux measurements under field conditions

Abstract. Four gas analysers capable of measuring nitrous oxide (N2O) concentration at a response time necessary for eddy covariance flux measurements were operated from spring until winter 2011 over a field cultivated with reed canary grass (RCG, Phalaris arundinacea, L.), a perennial bioenergy crop in eastern Finland. The instruments were TGA100A (Campbell Scientific Inc.), CW-TILDAS-CS (Aerodyne Research Inc.), N2O / CO-23d (Los Gatos Research Inc.) and QC-TILDAS-76-CS (Aerodyne Research Inc.). The period with high emissions, lasting for about 2 weeks after fertilization in late May, was characterized by an up to 2 orders of magnitude higher emission, whereas during the rest of the campaign the N2O fluxes were small, from 0.01 to 1 nmol m−2 s−1. Two instruments, CW-TILDAS-CS and N2O / CO-23d, determined the N2O exchange with minor systematic difference throughout the campaign, when operated simultaneously. TGA100A produced the cumulatively highest N2O estimates (with 29% higher values during the period when all instruments were operational). QC-TILDAS-76-CS obtained 36% lower fluxes than CW-TILDAS-CS during the first period, including the emission episode, whereas the correspondence with other instruments during the rest of the campaign was good. The reasons for systematic differences were not identified, suggesting further need for detailed evaluation of instrument performance under field conditions with emphasis on stability, calibration and any other factors that can systematically affect the accuracy of flux measurements. The instrument CW-TILDAS-CS was characterized by the lowest noise level (with a standard deviation of around 0.12 ppb at 10 Hz sampling rate) as compared to N2O / CO-23d and QC-TILDAS-76-CS (around 0.50 ppb) and TGA100A (around 2 ppb). We identified that for all instruments except CW-TILDAS-CS the random error due to instrumental noise was an important source of uncertainty at the 30 min averaging level and the total stochastic error was frequently of the same magnitude as the fluxes when N2O exchange was small at the measurement site. Both instruments based on continuous-wave quantum cascade laser, CW-TILDAS-CS and N2O / CO-23d, were able to determine the same sample of low N2O fluxes with a high mutual coefficient of determination at the 30 min averaging level and with minor systematic difference over the observation period of several months. This enables us to conclude that the new-generation instrumentation is capable of measuring small N2O exchange with high precision and accuracy at sites with low fluxes.

Approach in Nonintrusive Type I Load Monitoring Using Subtractive Clustering

In this paper, a low-sampling-rate and nonintrusive appliance loads monitoring (NIALM), which required only few tuning parameters and which is little sensitive to the grid power noise, is presented. Using transformed active power transitions as features, the proposed approach is based on the subtractive clustering and the maximum likelihood classifier. In order to validate the NIALM, a 1 Hz sampling rate experimental data from the reference energy disaggregation dataset is selected. The validation results with six commonly found ON/OFF residential appliances indicate that the proposed approach is effective. In addition, the obtained results from a Monte Carlo simulation suggest that this approach is less sensitive to power grid noise than a $K$ -mean-based NIALM method.

Comparison of Global Navigation Satellite System Devices on Speed Tracking in Road (Tran)SPORT Applications.

Global Naavigation Satellite Systems (GNSS) are, in addition to being most widely used vehicle navigation method, becoming popular in sport-related tests. There is a lack of knowledge regarding tracking speed using GNSS, therefore the aims of this study were to examine under dynamic conditions: (1) how accurate technologically different GNSS measure speed and (2) how large is latency in speed measurements in real time applications. Five GNSSs were tested. They were fixed to a car's roof-rack: a smart phone, a wrist watch, a handheld device, a professional system for testing vehicles and a high-end Real Time Kinematics (RTK) GNSS. The speed data were recorded and analyzed during rapid acceleration and deceleration as well as at steady speed. The study produced four main findings. Higher frequency and high quality GNSS receivers track speed at least at comparable accuracy to a vehicle speedometer. All GNSS systems measured maximum speed and movement at a constant speed well. Acceleration and deceleration have different level of error at different speeds. Low cost GNSS receivers operating at 1 Hz sampling rate had high latency (up to 2.16 s) and are not appropriate for tracking speed in real time, especially during dynamic movements.

Indoor Ultra-Wide Band Network Adjustment using Maximum Likelihood Estimation

Abstract. This study is the part of our ongoing research on using ultra-wide band (UWB) technology for navigation at the Ohio State University. Our tests have indicated that the UWB two-way time-of-flight ranges under indoor circumstances follow a Gaussian mixture distribution that may be caused by the incompleteness of the functional model. In this case, to adjust the UWB network from the observed ranges, the maximum likelihood estimation (MLE) may provide a better solution for the node coordinates than the widely-used least squares approach. The prerequisite of the maximum likelihood method is to know the probability density functions. The 30 Hz sampling rate of the UWB sensors enables to estimate these functions between each node from the samples in static positioning mode. In order to prove the MLE hypothesis, an UWB network has been established in a multi-path density environment for test data acquisition. The least squares and maximum likelihood coordinate solutions are determined and compared, and the results indicate that better accuracy can be achieved with maximum likelihood estimation.

녹색광을 이용한 반사형 광용적맥파측정기의 주변광 간섭시 신호측정

The purpose of this study is to verify the utility of reflected photoplethysmography sensor using two green light emitting diodes that influenced by ambient light. Recently it has been studied that green light emitting diode is suitable for light source of reflected photoplethysmography sensor at low temperature and high temperature. Another study showed that, green light is better for monitoring heart rate during motion than led light. However, it has a bad characteristic about ambient light noise. To verify the utility of reflected photoplethysmography sensor using green light emitting diode, this study measures the photoplethysmography signal that is distorted by ambient light and will propose a solution. This study has two parts of research method. One is measurement system that composed sensor and board. The sensor is made up PE-foam and Non-woven fabric for flexible sensor. The photoplethysmography signal is measured by measurement board that composed high-pass filter, low-pass filter and amplifier. Ambient light source is light bulb and white light emitting diode that has three steps brightness. Photoplethysmography signal is measured with lead II electrocardiography signal at the same time and it is measured at the finger and radial artery for 1 minute, 1000 Hz sampling rate. The lead II electrocardiography signal is a standard signal for heart rate and photoplethysmography signal that measured at the finger is a standard signal for waveform. The test is repeated 3 times using three sensor. The data is processed by MATLAB to verify the utility by comparing the correlation coefficient score and heart rate. The photoplethysmography sensor using two green light emitting diodes is shown better utility than using one green light emitting diode and red light emitting diode at the ambient light. The waveform and heart rate that measured by two green light emitting diodes are more identical than others. The amount of electricity used is less than red light emitting diode and error peak detectability factor is the lowest.

COTS-Based Stick-On Electricity Meters for Building Submetering

We demonstrate a low-cost, 19 mm × 12 mm prototype peel-and-stick electricity meter (PASEM) PCB to replace traditional in-circuit-breaker-panel current and voltage sensors for building submetering. The PASEM sensors are installed on the external face of circuit breakers to generate voltage and current signals at a 1920 Hz sample rate. This allows for the computation of real and apparent power as well as capturing harmonics created by nonlinear loads. The prototype sensor is built using commercially available components, resulting in a component cost of under $10 per PASEM in moderate quantities. With no high-voltage install work requiring an electrician, this leads to an installed system cost that is roughly ten times lower than traditional submetering technology. Measurement results from lab characterization as well as a real-world residential dwelling installation are presented, verifying the operation of our proposed PASEM sensor. The PASEM sensor can resolve breaker power levels below 10 W and consumes ~16 mA from a 5 V supply.

Operating an atom-interferometry-based gravity gradiometer by the dual-fringe-locking method

We report a gravity gradiometer composed of two atom interferometers which are simultaneously locked to the respective fringe center by feedback control of the Raman laser phase and magnetic field gradient. Compared with the conventional full-fringe recording method, this dual-fringe-locking strategy is capable of increasing the sampling rate and improving the sensitivity for gravity gradient measurements. Meanwhile, it retains the intrinsic advantage of rejecting common mode noises for gravity gradiometers. A short-term sensitivity of $670 \mathrm{E}/{Hz}^{1/2}$ with a 0.25 Hz sampling rate is achieved in our gravity gradiometer. This approach may also find possible applications in other atom-interferometry-based experiments utilizing dual atomic clouds.

Optimization‐based autonomous racing of 1:43 scale RC cars

SummaryThis paper describes autonomous racing of RC race cars based on mathematical optimization. Using a dynamical model of the vehicle, control inputs are computed by receding horizon based controllers, where the objective is to maximize progress on the track subject to the requirement of staying on the track and avoiding opponents. Two different control formulations are presented. The first controller employs a two‐level structure, consisting of a path planner and a nonlinear model predictive controller (NMPC) for tracking. The second controller combines both tasks in one nonlinear optimization problem (NLP) following the ideas of contouring control. Linear time varying models obtained by linearization are used to build local approximations of the control NLPs in the form of convex quadratic programs (QPs) at each sampling time. The resulting QPs have a typical MPC structure and can be solved in the range of milliseconds by recent structure exploiting solvers, which is key to the real‐time feasibility of the overall control scheme. Obstacle avoidance is incorporated by means of a high‐level corridor planner based on dynamic programming, which generates convex constraints for the controllers according to the current position of opponents and the track layout. The control performance is investigated experimentally using 1:43 scale RC race cars, driven at speeds of more than 3 m/s and in operating regions with saturated rear tire forces (drifting). The algorithms run at 50 Hz sampling rate on embedded computing platforms, demonstrating the real‐time feasibility and high performance of optimization‐based approaches for autonomous racing. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Role of ictal baseline shifts and ictal high-frequency oscillations in stereo-electroencephalography analysis of mesial temporal lobe seizures.

To assess the role of ictal baseline shifts (IBS) and ictal high-frequency oscillations (iHFOs) in intracranial electroencephalography (EEG) presurgical evaluation by analysis of the spatial and temporal relationship of IBS, iHFOs with ictal conventional stereo-electroencephalography (icEEG) in mesial temporal lobe seizures (MTLS). We studied 15 adult patients with medically refractory MTLS who underwent monitoring with depth electrodes. Seventy-five ictal EEG recordings at 1,000 Hz sampling rate were studied. Visual comparison of icEEG, IBS, and iHFOs were performed using Nihon-Kohden Neurofax systems (acquisition range 0.016-300 Hz). Each recorded ictal EEG was analyzed with settings appropriate for displaying icEEG, IBS, and iHFOs. IBS and iHFOs were observed in all patients and in 91% and 81% of intracranial seizures, respectively. IBS occurred before (22%), at (57%), or after (21%) icEEG onset. In contrast, iHFOs occurred at (30%) or after (70%) icEEG onset. The onset of iHFOs was 11.5 s later than IBS onset (p < 0.0001). All of the earliest onset of IBS and 70% of the onset of iHFOs overlapped with the ictal onset zone (IOZ). Compared with iHFOs, interictal HFOs (itHFOs) were less correlated with IOZ. In contrast to icEEG, IBS and iHFOs had smaller spatial distributions in 70% and 100% of the seizures, respectively. An IBS dipole was observed in 66% of the seizures. Eighty-seven percent of the dipoles had a negative pole at the anterior/medial part of amygdala/hippocampus complex (A-H complex) and a positive pole at the posterior/lateral part of the A-H complex. The results suggest that evaluation of IBS and iHFOs, in addition to routine icEEG, helps in more accurately defining the IOZ. This study also shows that the onset and the spatial distribution of icEEG, IBS, and iHFOs do not overlap, suggesting that they reflect different cellular or network dynamics.

A biomechanical research of foot pressure for lower extremity in gait wearing trail walking shoes

The aim of this study is to analyze foot pressure distribution of trail walking shoes while walking. Hiking, a recreational activity which is able to exercise whole body in the nature without any cost, has compositive effects which can reduce stress, strengthen muscles of entire body and improve cardiopulmonary function [1]. The Topography is hard near the surface and has rough characteristic because of rocks. These condition can lead to injuries to feet in hiking and aggravating fatigability of foot when people hike for a long time [2],so hiking boots which are specially functioned are encouraged because walking on the rough surface has latent dangerousness of injury [3]. Trail walking shoes generally provide more stability and support than regular walking shoes. Trail walking shoes are for natural trails. In rocky, rooted, dusty and muddy trails, a trail walking shoe gives added traction and support. Ten healthy males participated in this study. All subjects were free of lower extremity pain, history of serious injuries or operative treatment or subjective symptoms interfering with walking. Each subject wore four different shoe types during walking trials on a treadmill at a constant speed of 4.2km/hour. Pressure distribution data (contact area, maximum force, peak pressure, maximum mean pressure) were collected with pressure device at a sampling rate of 100Hz. Shoes used in the experiment are which developed in four shoes. Developed trail walking shoes (Type A), first developed trail walking shoes (Type B) and other company’s trail walking shoes (Type C, Type D) are selected for the experiment. Tested about ‘Comparison in Lightweightedness’ among the shoes (Figure ​(Figure1).1). ‘Comparison in Lightweightedness’s result is Type A (324.92 g) < Type B (350.70 g) < Type C (374.67 g) < Type D (397.16 g). Figure 1 Type A: developed trail walking shoes, Type B: first developed trail walking shoes, Type C, D: other company’s trail wxalking shoes Table 1 Result of Foot Pressure Contact area of functional shoes (Type A) increased in comparison to general shoes (Type C, Type D). At the same time, foot pressure decreased in comparison to general shoes (Type C, Type D). It is expected that Type A Functional shoes give more comfort and fit by increasing the contact area and decreasing peak pressure. In the result of the analysis of plantar pressure, Type A reported higher than other shoes on the forefoot. At the maximum force, Type A is observed as the smallest maximum force in almost part. These results, which is similar to Park (2009)’s research [3], decreased the confining pressure which can lead the deformation of forefoot’s toe. In the maximum pressure result, the outcome is similar to maximum force, which the smallest is Type A < Type D < Type B < Type C. This can decline the impulse which occurs in heel strike section, as a result, this can decrease the fatigability of foot in long-time walking. In addition, similar to Oh and Lee (2009)’s research [4], it can lighten the impulse force delivered to the body, as being the important factor which can decrease the weight to the leg joint. As examining the result of the average pressure, Type A < Type C < Type D < Type B is observed. In this thesis, we analyzed the contact area of plantar pressure, maximum force, maximum pressure, average pressure. Through this result, we can know impact force alleviation for foot and physical fatigue, too. When considering the pressure change of the foot, Type A’s contact area of foot is wider than the others. So, its wearing feeling will be better than the others. In case of maximum pressure, it is lower than the others and mid foot, hind foot’s result is similar. So, we expect ‘shockproof and to disperse pressure’ will be good. Also, with foot and shoe contact area’s increase, there may be amaximum force and maximum pressure decrease. So, it can decrease the foot’s and pelvic limb’s fatigue. We offer the data of the dispersing pressure functionality of walking hiking shoes, so it can be of help to a product’s functionality improvement.

An analysis of functional insole on foot pressure distribution of shape memory material combinations

The purpose of this study was to analyze foot pressure distribution of shape memory materials functional insole. Comfort is an important aspect for footwear and insole. Footwear and insole comfort has an influence on injury [1,2]. The development of new materials is considered as the important point for manufacturing functional insole [3,4]. Ten healthy male (mean height: 174.7±4.0 cm, mean body mass: 71.0±8.0 kg, mean age 23.9±0.3 yrs.) were participated in this study. All subjects were free of lower extremity pain, history of serious injuries or operative treatment or subjective symptoms interfering with walking. Each subject's foot was pre-screened by Podoscopy (Alfoots, Korea) to see if they had any foot abnormalities. The subjects were required to normal walking (4.2km/h) for treadmill. Each subjects was seven different insole type (A ~G type, figure ​figure1)1) during walking. The PEDAR®-X insole system (Novel GmbH, Germany) was used to measure the foot pressure and force. Pressure distribution data (peak pressure, maximum mean pressure) was collected with pressure device at a sampling rate of 100Hz. The feet were divided into six regions: foot (Total), lateral forefoot (M1), medial forefoot (M2), midfoot (M3), lateral rearfoot (M4), and medial rearfoot (M5). Figure 1 Tested seven types insoles (L-R): Type A ~ G. N: normal material, S1: low hardness shape memory material, S2: high hardness shape memory material, P1: low hardness Poron® material, P2: high hardness Poron® material. Comparison of foot pressure is show in figure ​figure2.2. In the midfoot (M3) area, a significant different was found between insoles in peak pressure and maximum mean pressure. The type F and G insoles decreased the peak pressure and maximum mean pressure. Figure 2 Comparison of foot pressure of the seven types insoles.

S-, M- and L-cone contributions to human pupil responses under dim illumination conditions

Cones, rods and melanopsin contribute to pupillary responses. However, how each type of cones contributes to pupil responses has been rarely studied. In our study, we investigated pupil responses to S-, M- and L-cone flicker inputs under dim illumination conditions. A four-primary Ganzfeldphotostimulator (DiagnosysColorDome) controlled rod and cone stimulations at −0.9 log cd/m2, which is below the melanopsin threshold but above the cone detection threshold. Four types of sinusoidally modulated stimuli (1 Hz, 20% contrast) were used: 1) rod stimuli (modulated rod excitation with a constant S- M- and L-cone excitation); 2) S-cone stimuli (modulated S-cone excitation; constant rod, M- and L-cone excitation); 3) M-cone stimuli (modulated M-cone excitation; constant rod, S- and L-cone excitation); and 4) L-cone stimuli (modulated L-cone excitation; constant rod, S- and M-cone excitation). Pupil sizes were measured using an Eyelink II eyetracker (SR Research) with a 250 Hz sampling rate. Pupil amplitudes and phases were derived by Fourier analysis. The results showed that, overall, the cone (S-, M- or L-) stimuli produced smaller responses than rod stimuli, suggesting rod dominance at −0.9 cd/m2. On the other hand, pupil responses to the M-cone stimuli were larger than for S- or L-cone stimuli. While the M- and L-cone stimuli produced similar response phases (between 0 deg and −50 deg), the S-cone stimuli had a response phase of approximately 180 deg. These results are consistent with L/M-On and S-OFF response characteristics of ipRGCs measured in primate retinas (Dacey et al., 2005).

Crack Growth Monitoring in Ceramic Matrix Composites by Combined Infrared Thermography and Acoustic Emission

The current study proposes a novel methodology for measuring crack growth in composite materials using combined infrared thermography (IRT) and acoustic emission (AE). The technique is tested across a SiC‐fiber‐reinforced ceramic matrix composite while no apparent factor is limiting its usage on composite materials of different nature as well. Compact tension specimens were loaded in tension with unloading/reloading loops and the thermally dissipated energy due to crack growth and other damage mechanisms was captured by IRT with a 100 Hz sampling rate. Crack growth was established by identifying the time instances where the maximum temperature, hence also damage, occurred and then quantifying, by means of control lines, the damage span within the thermograph corresponding to the specific instance. The high accuracy of the proposed technique was validated against optical measurements of crack length. The theoretical crack length predicted by the elastic compliance technique was found to overestimate the experimental findings by at least 25%. Knowledge of the critical level of damage accumulation for material structural health was made possible from AE descriptors such as activity during the unloading part of the cycles. In this study, AE was particularly successful in closely following the actual crack growth measured by IRT, an observation that brings out the potential of the technique for quantitative measurements.

From pole to pole: Soundscapes of the Atlantic Ocean

Between July 2009 and December 2010, two identical calibrated hydrophone packages were deployed and continuously operated (2,000 Hz sampling rate) in the Fram Strait (79°N, 5.5°E) and the Bransfield Strait (62°S, 55.5°W). Analysis of these recordings were combined with a data set collected during the same time period by the Comprehensive Nuclear-Test-Ban Treaty Organization International Monitoring System (CTBTO IMS) hydroacoustic station HA10 (250 Hz sampling rate) at Ascension Island (8°S, 14.4°W). The combination of these datasets allowed a comparison of low-frequency noise levels in polar and tropic areas of the Atlantic Ocean. The recordings were analyzed for major natural (e.g., marine mammals, ice) and anthropogenic (e.g., shipping, seismic) contributors to the ambient sound field and their seasonal variability. Preliminary results indicate (1) a higher seasonal variability of ambient noise levels in polar regions compared to the tropics, (2) the seasonal variability of ambient noise levels in the Arctic and Antarctic were driven by different contributors, and (3) highest noise levels were observed in the Arctic in association with seismic oil and gas exploration. [Partial funding from NOAA/PMEL and the Korea Polar Research Institute.]

Intracranial electroencephalographic seizure-onset patterns: effect of underlying pathology

Because seizures originate from different pathological substrates, the question arises of whether distinct or similar mechanisms underlie seizure generation across different pathologies. Better defining intracranial electroencephalographic morphological patterns at seizure-onset could improve the understanding of such mechanisms. To this end, we investigated intracranial electroencephalographic seizure-onset patterns associated with different epileptogenic lesions, and defined high-frequency oscillation correlates of each pattern. We analysed representative seizure types from 33 consecutive patients with drug-resistant focal epilepsy and a structural magnetic resonance imaging lesion (11 mesial temporal sclerosis, nine focal cortical dysplasia, six cortical atrophy, three periventricular nodular heterotopia, three polymicrogyria, and one tuberous sclerosis complex) who underwent depth-electrode electroencephalographic recordings (500 Hz filter, 2000 Hz sampling rate). Patients were included only if seizures arose from contacts located in lesional/peri-lesional tissue, and if clinical manifestations followed the electrographic onset. Seizure-onset patterns were defined independently by two reviewers blinded to clinical information, and consensus was reached after discussion. For each seizure, pre-ictal and ictal sections were selected for high-frequency oscillation analysis. Seven seizure-onset patterns were identified across the 53 seizures sampled: low-voltage fast activity (43%); low-frequency high-amplitude periodic spikes (21%); sharp activity at ≤13 Hz (15%); spike-and-wave activity (9%); burst of high-amplitude polyspikes (6%); burst suppression (4%); and delta brush (4%). Each pattern occurred across several pathologies, except for periodic spikes, only observed with mesial temporal sclerosis, and delta brush, exclusive to focal cortical dysplasia. However, mesial temporal sclerosis was not always associated with periodic spikes nor focal cortical dysplasia with delta brush. Compared to other patterns, low-voltage fast activity was associated with a larger seizure-onset zone (P = 0.04). Four patterns, sharp activity at ≤13 Hz, low-voltage fast activity, spike-and-wave activity and periodic spikes, were also found in regions of seizure spread, with periodic spikes only emerging from mesial temporal sclerosis. Each of the seven patterns was accompanied by a significant increase in high-frequency oscillations upon seizure-onset. Overall, our data indicate that: (i) biologically-distinct epileptogenic lesions share intracranial electroencephalographic seizure-onset patterns, suggesting that different pathological substrates can affect similarly networks or mechanisms underlying seizure generation; (ii) certain pathologies are associated with intracranial electroencephalographic signatures at seizure-onset, e.g. periodic spikes which may reflect mechanisms specific to mesial temporal sclerosis; (iii) some seizure-onset patterns, including periodic spikes, can also be found in regions of spread, which cautions against relying on the morphology of the initial discharge to define the epileptogenic zone; and (iv) high-frequency oscillations increase at seizure-onset, independently of the pattern.

Variations of pupil centration and their effects on video eye tracking

To evaluate measurement errors that are introduced in video eye tracking when pupil centration changes with pupil size. Software was developed under Visual C++ to track both pupil centre and corneal centre at 87 Hz sampling rate at baseline pupil sizes of 4.75 mm (800 lux room illuminance) and while pupil constrictions were elicited by a flashlight. Corneal centres were determined by a circle fit through the pixels detected at the corneal margin by an edge detection algorithm. Standard deviations for repeated measurements were ± 0.04 mm for horizontal pupil centre position and ± 0.04 mm for horizontal corneal centre positions and ±0.03 mm for vertical pupil centre position and ± 0.05 mm for vertical corneal centre position. Ten subjects were tested (five female, five male, age 25-58 years). At 4 mm pupil sizes, the pupils were nasally decentred relative to the corneal centre by 0.18 ± 0.19 mm in the right eyes and -0.14 ± 0.22 mm in the left eyes. Vertical decentrations were 0.30 ± 0.30 mm and 0.27 ± 0.29 mm, respectively, always in a superior direction. At baseline pupil sizes (the natural pupil sizes at 800 lux) of 4.75 ± 0.52 mm, the decentrations became less (right and left eyes: horizontal 0.17 ± 0.20 mm and -0.12 ± 0.22 mm, and vertical 0.26 ± 0.28 mm and 0.20 ± 0.25 mm). While pupil decentration changed minimally in eight of the subjects, it shifted considerably in two others. Averaged over all subjects, the shift of the pupil centre position per millimetre pupil constriction was not significant (right and left eyes: -0.03 ± 0.07 mm and 0.03 ± 0.04 mm nasally per mm pupil size change, respectively, and -0.04 ± 0.06 mm and -0.05 ± 0.12 mm superiorly). Direction and magnitude of the changes in pupil centration could not be predicted from the initial decentration at baseline pupil sizes. In line with data in the literature, the pupil centre was significantly decentred relative to the corneal centre in the nasal and superior direction. Pupil decentration changed significantly with pupil size by 0.05 mm on average for 1 mm of constriction. Assuming a Hirschberg ratio of 12° mm(-1) , a shift of 0.05 mm is equivalent to a measurement error in a Purkinje image-based eye tracker of 0.6°. However, the induced measurement error could also exceed 1.5° in some subjects for only a 1 mm change in pupil size.