Amplitude Change Rate Research Articles

Scour diagnosis index based on cross-correlation analysis of bridge dynamic response under vehicle braking

Several innovative scour diagnostic indexes are proposed based on the cross-correlation analysis for bridge dynamic response excited by vehicle braking. Firstly, a vehicle-bridge coupled vibration model considering vehicle braking is established and its accuracy is verified by a field loading test. Secondly, the fixed shape characteristic of cross-correlation function amplitude vector of the braking-induced dynamic response is theoretically deduced and verified numerically with a continuous girder bridge example considering various test parameters, which is the basic for scour diagnosis. Further, two scour diagnostic indexes are proposed, one is the cross-correlation function amplitude change rate vector, which is used to identify the scour location with a threshold of 2%, and the other is the transversal cross-correlation function amplitude change rate vector, which is used to identify the scour uniformity. The good applicability and accuracy of proposed indexes for different scour states is verified by numerical simulation for above bridge example. The proposed diagnostic indexes are very sensitive to foundation scour and have strong error tolerance for test parameters. The dynamic response required for scour diagnosis can be obtained with regular bridge loading test.

Seismic Response Analysis of Uplift Terrain under Oblique Incidence of SV Waves

In order to analyze the impact of seismic waves on the venue earthquake, based on the display finite element method, the viscoelastic artificial boundary is used to analyze the variation of the ground motion amplification coefficient and the Fourier spectrum of the raised terrain under different incident angles with SV wave oblique incidence on different slopes. This verification model analysis solution and numerical solution are better. The numerical simulation results show that as the degree of the slope increases, the seismic amplification coefficient increases, and its slope amplification coefficient changes significantly. The X direction coefficient is greater than Y’s magnification coefficient. The Fourier curve with a frequency of 0.2~1 Hz increases with the slope of the raised terrain; when the El Centro is incorporated at 30°, the Fourier spectrum amplitude decreases as the incident angle increases in the low-frequency band. The amplitude of the Fourier spectrum at the high-frequency band monitoring point changes with the incident angle. In the high-frequency band from 1 to 10 Hz, the rate of amplitude change is the largest. When the incident angle is at 0°, the amplification coefficient in the Y direction is basically symmetric.

Cortical Responses to the Amplitude Envelopes of Sounds Change with Age.

Many older listeners have difficulty understanding speech in noise, when cues to speech-sound identity are less redundant. The amplitude envelope of speech fluctuates dramatically over time, and features such as the rate of amplitude change at onsets (attack) and offsets (decay), signal critical information about the identity of speech sounds. Aging is also thought to be accompanied by increases in cortical excitability, which may differentially alter sensitivity to envelope dynamics. Here, we recorded electroencephalography in younger and older human adults (of both sexes) to investigate how aging affects neural synchronization to 4 Hz amplitude-modulated noises with different envelope shapes (ramped: slow attack and sharp decay; damped: sharp attack and slow decay). We observed that subcortical responses did not differ between age groups, whereas older compared with younger adults exhibited larger cortical responses to sound onsets, consistent with an increase in auditory cortical excitability. Neural activity in older adults synchronized more strongly to rapid-onset, slow-offset (damped) envelopes, was less sinusoidal, and was more peaked. Younger adults demonstrated the opposite pattern, showing stronger synchronization to slow-onset, rapid-offset (ramped) envelopes, as well as a more sinusoidal neural response shape. The current results suggest that age-related changes in the excitability of auditory cortex alter responses to envelope dynamics. This may be part of the reason why older adults experience difficulty understanding speech in noise.SIGNIFICANCE STATEMENT Many middle-aged and older adults report difficulty understanding speech when there is background noise, which can trigger social withdrawal and negative psychosocial health outcomes. The difficulty may be related to age-related changes in how the brain processes temporal sound features. We tested younger and older people on their sensitivity to different envelope shapes, using EEG. Our results demonstrate that aging is associated with heightened sensitivity to sounds with a sharp attack and gradual decay, and sharper neural responses that deviate from the sinusoidal features of the stimulus, perhaps reflecting increased excitability in the aged auditory cortex. Altered responses to temporal sound features may be part of the reason why older adults often experience difficulty understanding speech in social situations.

Passive Microwave Biosensor for Real-Time Monitoring of Subsurface Bacterial Growth.

A real-time and label-free microstrip sensor capable of detecting and monitoring subsurface growth of Escherichia coli (E. coli) on solid growth media such as Luria-Bertani (LB) agar is presented. The microwave ring resonator was designed to operate at 1.76GHz to detect variations in the dielectric properties such as permittivity and loss tangent to monitor bacterial growth. The sensor demonstrated high efficiency in monitoring subsurface dynamics of E. coli growth between two layers of LB agar. The resonant amplitude variations (Δ Amplitude (dB)) were recorded for different volumes of E. coli (3μL and 9μL) and compared to control without E. coli for 36 hours. The control showed a maximum amplitude variation of 0.037dB, which was selected as a threshold to distinguish between the presence and absence of E. coli growth. The measured results by sensors were further supported by microscopic images. It is worth noticing that the amplitude variations fit well with the Gompertz growth model. The rate of amplitude change correlating bacteria growth rate was calculated as 0.08 and 0.13dB/hr. for 3μL and 9μL of E. coli, respectively. This work is a proof of concept to demonstrate the capability of microwave sensors to detect and monitor subsurface bacterial growth.

Research on Dual Mode Unified Control Strategy of Grid Connected Inverter Based on Droop Control

There is a big difference between the two modes of grid connected inverter in micro-grid operation. In order to avoid large voltage and current impact, advanced control strategy is needed to realize smooth conversion during operation mode switching. A droop control method based on voltage amplitude change rate is proposed, which is suitable for dual-mode unified control of inverter. While ensuring the stability of the system, the reactive power of the inverter can be accurately shared during islanding operation. This method can realize smooth switching between grid connected inverter and islanding mode. The feasibility of the method is verified by simulation and experiment.

Effectiveness of vergence/accommodative therapy for accommodative dysfunction in children with convergence insufficiency.

To determine the effectiveness of office-based vergence/accommodative therapy for improving accommodative amplitude and accommodative facility in children with symptomatic convergence insufficiency and accommodative dysfunction. We report changes in accommodative function following therapy among participants in the Convergence Insufficiency Treatment Trial - Attention and Reading Trial with decreased accommodative amplitude (115 participants in vergence/accommodative therapy; 65 in placebo therapy) or decreased accommodative facility (71 participants in vergence/accommodative therapy; 37 in placebo therapy) at baseline. The primary analysis compared mean change in amplitude and facility between the vergence/accommodative and placebo therapy groups using analyses of variance models after 4, 8, 12 and 16weeks of treatment. The proportions of participants with normal amplitude and facility at each time point were calculated. The average rate of change in amplitude and facility from baseline to week 4, and from weeks 4 to 16, were determined in the vergence/accommodative therapy group. From baseline to 16weeks, the mean improvement in amplitude was 8.6 dioptres (D) and 5.2D in the vergence/accommodative and placebo therapy groups, respectively (mean difference=3.5D, 95% confidence interval (CI): 1.5 to 5.5D; p=0.01). The mean improvement in facility was 13.5 cycles per minute (cpm) and 7.6cpm in the vergence/accommodative and placebo therapy groups, respectively (mean difference=5.8cpm, 95% CI: 3.8 to 7.9cpm; p<0.0001). Significantly greater proportions of participants treated with vergence/accommodative therapy achieved a normal amplitude (69% vs. 32%, difference=37%, 95% CI: 22 to 51%; p<0.0001) and facility (85% vs. 49%, difference=36%, 95% CI: 18 to 55%; p<0.0001) than those who received placebo therapy. In the vergence/accommodative therapy group, amplitude increased at an average rate of 1.5D per week during the first 4weeks (p<0.0001), then slowed to 0.2D per week (p=0.002) from weeks 4 to 16. Similarly, facility increased at an average rate of 1.5cpm per week during the first 4weeks (p<0.0001), then slowed to 0.6cpm per week from weeks 4 to 16 (p<0.0001). Office-based vergence/accommodative therapy is effective for improving accommodative function in children with symptomatic convergence insufficiency and coexisting accommodative dysfunction.

Spatial velocity of the dynamic vectorcardiographic loop provides crucial insight in ventricular dysfunction

Vectorcardiogram (VCG) represents the trajectory of the tip of cardiac vectors in three dimensional space with varying time. It is a recurring, near-periodic pattern of cardiac dynamics that is constructed by drawing the instantaneous vectors from a zero reference point according to direction, magnitude and polarity in the space. Being a three dimensional entity, it is more informative and more sensitive than conventional ECG as an evaluation tool of the physiology of cardiac dynamics, because of its extra degree of freedom. Accordingly, it is possible to find out even a minute and early electrophysiological alteration in diseases.Each cardiac cycle primarily consists of three loops in VCG corresponding to P, QRS, and T wave activities. The morphological assessment of the QRS loop was carried out in three dimensional space in order to analyze the spatial vectors of the ventricles and their patho-physiological correlation in various cardiac diseases.Spatial Velocity (SV) is a virtual velocity that represents the rate of movement of the tip of the cardiac vector through space, coordinated by three orthogonal leads, and can be estimated by using simple mathematical formula. It is the rate of change in amplitude and the directionality of instantaneous vectors in seriatim in the three dimensional space to quantify their the temporo-spatial characteristic pattern.We propose to evaluate this novel VCG descriptor SV, in normal individuals and patients of ventricular dysfunction. The possible mechanisms consistent with the patho-physiological basis of ventricular dysfunction or heart failure with altered SV would enrich the current understanding of the disease.Heart failure is the final common pathway of multitude of cardiac pathologies. Despite etiological heterogeneity, there are common mechanisms involved in the complex electrophysiological alteration of the failing myocardium. The changes observed as a consequence of ventricular dysfunction involve ion channel remodeling, intercellular uncoupling, myocardial ischemia, alterations in calcium handling, remodeling of the extracellular matrix, the presence of scars, activation of the sympathetic & the renin–angiotensin–aldosterone system, dilatation as well as stretch of viscous etc. The source modulation of the depolarization wave and its propagation in the heart and body fluid volume conductor also influence the visual pattern of cardiac vectors. In addition, patients with heart failure receive pharmacological or non-pharmacological therapies that also influence the electrophysiological changes.We hypothesize that the spatial velocity of ventricular depolarization and repolarization vectors of the VCG loop alters with a characteristic pattern in the patients with ventricular dysfunction and can differentiate healthy individuals from patients with ventricular dysfunction and also differentiate various categories, gradations and severity stratifications of the patients with ventricular dysfunction.

A combined method for instantaneous frequency identification in low frequency structures

Civil engineering structures such as high-rise buildings and long-span cable-supported bridges usually exhibit low-frequency characteristics and the resultant response signals may be non-asymptotic (the amplitude change rate is higher than its phase change rate) and even have closely-spaced frequency components. The identification of satisfactory instantaneous frequencies of such response signals is a challenge faced by standard synchrosqueezing wavelet transform. The paper aims to propose a combined method to address this challenge. The proposed method combines an extended analytical mode decomposition (AMD) method, a recursive Hilbert transform and a zoom synchrosqueezing wavelet transform (consisting of frequency-shift operation and partial zoom synchrosqueezing operation). In the method, a multi-component signal, which may consist of closely spaced frequency components, is firstly decomposed into several mono-component signals by the extended AMD, and the extracted mono-components are then demodulated into asymptotic signals by recursively using the Hilbert transform. After that, a frequency-shift operation is employed to improve time resolution and a partial zoom synchrosqueezing operation is then applied to improve the frequency resolution in the narrow low frequency range of interest. Two numerical examples, an experiment on an aluminum cantilever beam with abrupt mass reduction and an experiment on a cable with time-varying tension forces are provided to illustrate the effectiveness, accuracy and robustness of the method.

Efficient Fiducial Point Detection of ECG QRS Complex Based on Polygonal Approximation.

Electrocardiogram signal analysis is based on detecting a fiducial point consisting of the onset, offset, and peak of each waveform. The accurate diagnosis of arrhythmias depends on the accuracy of fiducial point detection. Detecting the onset and offset fiducial points is ambiguous because the feature values are similar to those of the surrounding sample. To improve the accuracy of this paper’s fiducial point detection, the signal is represented by a small number of vertices through a curvature-based vertex selection technique using polygonal approximation. The proposed method minimizes the number of candidate samples for fiducial point detection and emphasizes these sample’s feature values to enable reliable detection. It is also sensitive to the morphological changes of various QRS complexes by generating an accumulated signal of the amplitude change rate between vertices as an auxiliary signal. To verify the superiority of the proposed algorithm, error distribution is measured through comparison with the QT-DB annotation provided by Physionet. The mean and standard deviation of the onset and the offset were stable as ms and ms, respectively. The results show that proposed method using small number of vertices is acceptable in practical applications. We also confirmed that the proposed method is effective through the clustering of the QRS complex. Experiments on the arrhythmia data of MIT-BIH ADB confirmed reliable fiducial point detection results for various types of QRS complexes.

Method for the measurement of the stratification of concentrated suspensions

A simple, fast and precise method for evaluation of precipitate formation kinetics and its amount in concentrated suspensions that are stored in closed containers after production has been developed. The method is based on the measurement of the mechanical pendulum period change over time. The principles of the development of this method are presented: theoretical fundamentals of measurement using this method have been analyzed; it was proved that the swing period and amplitude change rate are informative pendulum parameters; a pendulum variant was determined experimentally that allows to avoid the error introduced by the movement of suspension inside the container and reduces the requirements for the container mass uniformity; it was determined that in order to reduce the error it is appropriate to start the period duration measurement from the 5 period from the beginning of the swing; the dependence of the swing period on the mass of the precipitate was evaluated experimentally.

VPT‐60: A novel approach to monitoring peripheral nerve sensitivity

Peripheral nerve sensitivity (PNS) can be used as an indicator of nerve loss or damage known as peripheral neuropathy. Because peripheral neuropathy can result in morbidity and mortality, accurate monitoring of PNS is imperative.A review of the literature has shown that variables such as age, sex, compression force and temperature can effect PNS. Neither of the two clinical reference standards [Semmes‐Weinstein Monofilaments (SWM) or Bio‐Thesiometer (BT)] take these variables into account in determining PNS.We developed a novel instrument, VPT‐60, that measures PNS, temperature and compression force of a digit. It can vary the frequency of vibration and the rate of amplitude change among other variables.The correlation of these variables with PNS was analyzed in 41 subjects that exhibited a wide range of characteristics. We found a statistically significant correlation coefficient between VPT‐60 PNS and age [0.52 (p=0.001)]; sex [0.33 (p=0.03)]; finger weight [−0.045 (p=0.005)]; and finger temperature [0.34 (p=0.03)]. While the VPT‐60 had a significant correlation with both the SWM (0.75) and the BT (0.86), the BT correlation with SWM was only 0.51. At 60 Hz vibration, the VPT‐60 had a higher correlation with SWM than did the BT at 120 Hz.In this study, the VPT‐60 appeared to provide a better approach to determining peripheral nerve sensitivity and the factors that effect it than the SWM or BT.

보코더에서 피치검색 성능개선에 관한 연구

보코더 에서 의 피치 분석 과정은 매우 중요하다. 일반적으로 먼저 신호의 주기성을 강조한 후 피치를 검색하는 방법을 주로 사용한다. 프레임 내에서 두 개의 펄스 간격을 변화시켜가며 신호와의 상관관계를 구하는 것으로 상관관계 값이 가장 높을 때가 주기가 가장 두드러지는 반복 구간이므로 이때 의 펄스 간격을 피치 주기로 찾는다. 그러나 찾아진 주기가 반주기, 배주기 및 세배주기인 경우에는 이 간격을 피치 주기라 할 수 없어 이를 해결하기 위한 여러 가지방법들이 제안되어있다. 또한 프레임 내에서의 신호의 진폭이 일정하지 않고 갑자기 변하는 구간이 있는 경우 정확하지 않는 피치가 얻어진다. 이를 해결하기 위해 프레임을 여러 개의 서브프레임으로 다시 나누어 피치를 검색하는 방법을 사용하고 있는데 이 방법은 피치를 정확하게 검색할 수 있지만 계산 량이 많아진다. 본 논문에서는 위에 제시한 두 가지 문제점을 개선하기 위한 알고리즘을 제안한다. 첫째 반주기, 배주기 및 세배주기를 줄이기 위해 피치를 검색하기 전에 프레임 내의 전체 에너지변화 비율을 추정하여 신호의 에너지 레벨을 미리 보상해 준 후 피치를 검색하는 방법을 제안한다. 둘째, 이렇게 구한 에너지 비율로 프레임 내의 진폭 변화율을 예측하여 서브프레임 수를 가변시키는 방법을 제안한다. 이 방법들을 적용하면 합성 음질에는 영향을 주지 않는 상태에서 피치검색 시간을 단축할 수 있고, 피치 검색의 정확도를 높일 수 있어 전반적인 피치 검색에 관한 성능 개선이 된다. The pitch searching is a vital process in a vocoder. Generally, the method of pitch searching is employed after highlighting the periodicity, where a correlation is identified with the signal by changing the interval of two pulses. When the correlation value reaches the peak, the pitch can be found by the pulse interval because it is the repetition interval with most striking period. However if the identified period happens to be one of half period, double period or triple period, this cannot be considered as the pitch period. Many methods were suggested to solve this problem. An inaccurate pitch could be obtained as well, when there is an interval where signal amplitude is not constant but varies abruptly in the frame. To solve this matter, searching the pitch by dividing a frame into various subframes is adopted, but too much calculation has to be followed while it leads the correct value. This paper suggests an algorithm to resolve these two problems. First, to search the pitch after advance correction of the signal energy level with an estimated overall energy change ratio in the frame before pitch search to reduce half period, double period and triple period is suggested. Second, to vary the number of subframes by predicting the amplitude change rate in the frame by the energy ratio obtained by the above-mentioned method is advised. If these two methods are applied, the pitch searching time can be reduced and the general pitch searching performance can be improved without affecting the sound quality in the synthesized signal.

보코더에서 서브프레임 수의 변화를 이용한 피치검색 성능 개선에 관한 연구

보코더에서의 피치 검색 과정은 매우 중요하다 . 일반적으로 먼저 신호의 주기성을 강조한 후 피치를 검색하는 방법을 주로 사용한다. 프레임 내에서 두 개의 펄스 간격을 변화시켜 가며 신호와의 상관관계를 구하는 것으로 상관관계 값이 가장 높을 때가 주기가 가장 두드러지는 반복 구간이므로 이때 의 펄스 간격을 피치 주기로 찾는다. 그러나 프레임 내에서의 신호의 진폭이 일정하지 않고 갑자기 변하는 구간이 있는 경우 정확하지 않는 피치가 얻어진다. 이를 해결하기 위해 프레임을 여러 개의 서브프레임으로 다시 나누어 피치를 검색하는 방법을 사용하고 있는데 이 방법은 피치를 정확하게 검색할 수 있지만 계산량이 많아진다. 본 논문에서는 프레임의 에너지 비율로 프레임 내의 진폭 변화율을 예측하여 서브프레임 수를 가변시키는 방법을 제안한다. 이 방법들을 적용하면 합성 음질에는 영향을 주지 않는 상태에서 피치검색 시간을 단축할 수 있고, 피치 검색의 정확도를 높일 수 있어 전반적인 피치 검색에 관한 성능 개선이 된다.

Alteration in Muscle Fatigue Caused by Load-Type Differences during Isometric Flexion of Human Fingers

We measured the endurance time and force and assessed the electromyograms of the flexor digitorum muscle and extensor digitorum muscle in response to 2 types of submaximal fatiguing. The 2 tasks involved isometric contraction of the proximal interphalangeal joint flexor muscles at 50% of the maximum voluntary contraction (MVC) force, which was achieved either by maintaining a constant force while pulling a force transducer (force task) or by supporting an equivalent load while maintaining a constant proximal interphalangeal joint angle (position task). Seven men performed the 2 tasks with their index, middle, and ring fingers. For all 3 fingers, the endurance time for the force task (79 ± 22, 93 ± 46, and 96 ± 56 s for the index, middle, and ring fingers, respectively) was shorter than the corresponding values for the position task (141 ± 105, 147 ± 82, and 212 ± 91 s). The rate of change in amplitude and mean power frequency in the electromyogram did not significantly differ across the 2 tasks. Physiological tremor was computed from the recorded force signal. The physiological tremor initially decreased during both tasks; however, the subsequent increase occurred earlier during the force task.

The relationship in gating effects between short-latency and long-latency somatosensory-evoked potentials

We investigated the relationship between short-latency and long-latency somatosensory-evoked potentials (SEPs) relating to voluntary movement. In general, the amplitudes of short-latency components in SEPs are attenuated during movement, whereas those of long-latency are enhanced, and this phenomenon is termed 'gating effects'. This study aimed to examine the relationship of changes in amplitude between short-latency and long-latency SEPs. SEPs were recorded from 11 participants at Fz, Cz, Pz, and C4' by stimulating the left median nerve. Two tasks were conducted; Control and Movement. In Control, the participant was asked to relax with no specific task. In Movement, the participant was encouraged to continue a rapid drumming motion of all fingers of the left hand at a self-paced rate. The amplitudes of short-latency SEPs, the P25 at C4' and N30 at Fz, were significantly smaller in the Movement than Control condition. By contrast, the amplitudes of long-latency SEPs, the N140 at Fz, Cz, and Pz were significantly larger in Movement than Control condition. Moreover, a significant positive correlation was observed in the rate of amplitude change between the frontal N30 and vertex N140, indicating that for the participants with a frontal N30 of smaller amplitude during Movement, the amplitude of the vertex N140 was smaller. We inferred that the neural activities in movement-related cortices affected the sources for the frontal N30 and vertex N140 in the same neuronal network simultaneously.

Low Voltage CMOS LC VCO with Switched Self-Biasing

This paper presents a switched self-biasing and a tail current-shaping technique to suppress the 1/f noise from a tail current source in differential cross-coupled inductance-capacitance (LC) voltage-controlled oscillators (VCOs). The proposed LC VCO has an amplitude control characteristic due to the creation of negative feedback for the oscillation waveform amplitude. It is fabricated using a 0.13 μm CMOS process. The measured phase noise is -117 dBc/Hz at a 1 MHz offset from a 4.85 GHz carrier frequency, while it draws 6.5 mA from a 0.6 V supply voltage. For frequency tuning, process variation, and temperature change, the amplitude change rate of the oscillation waveform in the proposed VCO is 2.1 to 3.2 times smaller than that of an existing VCO with a fixed bias. The measured amplitude change rate of the oscillation waveform for frequency tuning from 4.55 GHz to 5.04 GHz is 131 pV/Hz.

Auditory scene analysis based on time‐frequency integration of shared FM and AM (I): Lagrange differential features and frequency‐axis integration

AbstractWe will propose in this paper a new algorithm for a computational implementation of auditory scene analysis. This algorithm forms a three‐layer structure of (1) subband decomposition by wavelet transform, (2) characterization of subband signal fragments by instantaneous frequency, frequency change rate, and amplitude change rate, and (3) frequency integration of subband signal features by voting method. We will perform the grouping and integration by voting the subband signal fragments into a nonparametric multipeak probability density distribution expressing “possibility of streams”; and then the recognition of the streams and the extraction of the stream parameters are realized by tracing its greatest point. It is confirmed from basic experiments for synthesized sounds and voices that the fundamental frequency/frequency change rate/amplitude change rate can be separated and estimated from multiple streams. © 2002 Wiley Periodicals, Inc. Syst Comp Jpn, 33(11): 95–106, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.1167

Auditory scene analysis based on time‐frequency integration of shared FM and AM (II): Optimum time‐domain integration and stream sound reconstruction

AbstractIn the preceding paper, we have proposed a method for auditory scene analysis, in which the instantaneous frequency, frequency change rate, and amplitude change rate in time‐frequency space are intensified into a multipeak probability density distribution by voting method and the grouping into streams of mixed sounds is realized. In this paper, as the main point of the second half of this method, we will introduce the assumption that the stream parameters vary slowly according to the known dynamics and propose an integration method on the time axis, in which the probability density distribution of the stream parameters is optimally estimated in time series by a nonparametric Kalman filter. By doing so, the mechanism of higher auditory scene analysis such as enhancement of the accuracy of the stream parameters, interpolation and connection of the breaks of the streams, and introduction of a priori knowledge into stream selection can be realized. Moreover, the separation and reconstruction system of sounds which correspond to streams is constructed, and the proposed technique is verified by fundamental experiments for synthesized sounds or musical sounds and voices. © 2002 Wiley Periodicals, Inc. Syst Comp Jpn, 33(10): 83–94, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.1160

Impact of productivity events on the benthic foraminiferal fauna in the Arabian Sea over the last 150,000 years

We have studied the sediment geochemistry and benthic foraminiferal fauna in a piston core from the northwest Arabian Sea (covering the last 150,000 years), and compared the results with the stable isotopic record from both benthic (Uvigerina peregrina) and planktonic (Globigerinoides sacculifer) foraminifera. The δ18O record of the planktonic foraminiferal species shows excursions towards heavier δ18O values when compared to the benthic record and the SPECMAP stack, particularly in stage 3, between approximately 30 and 45–50 kyr. We call this the “stage 3 event.” Species diversity and relative abundance data on benthic foraminifera reveal that some species, e.g. Cibicidoides wuellerstorfi, Oridorsalis umbonatus, Pullenia bulloides, Pyrgo spp., and the uvigerinids increased in relative abundance during glacial stages 2 and 4 and during the stage 3 event, whereas other (e.g., Astrononion novozealandicum, Cibicidoides bradyi, Eggerella bradyi, Gyroidina altiformis, Hoeglundina elegans, Pullenia subcarinata, and Sigmoilina edwardsii) decreased. Using correspondence analysis we determined that approximately 50% of the total sample variation may be accounted for by three first factors which all are interpreted as primarily related to surface water productivity and the quality of the organic matter that reaches the seafloor. The relative abundance of some species appears to vary on a precessional cycle, perhaps responding to monsoon‐driven upwelling and associated increased food supply, whilst the abundances of other species are related to the 100 kyr ice volume cycle, and may be responding to changes in intermediate and deep water chemistry. Geochemical paleoproductivity tracers, such as the Ba content of the sediment, have a very similar distribution to specific foraminiferal factors in both time and frequency domains. Certain planktonic foraminifera, (e.g., Globigerina bulloides), also display obvious maxima in the stage 3 event. The stage 3 event occurs at a time of reduced rate of amplitude change in both solar radiation and monsoon pressure index. We conclude, that there was a period 15 to 20 kyr duration during stage 3 with cooler‐than‐normal surface waters, enhanced productivity and rapid settling of biogenic matter.

Evidence for multiple generators in evoked responses using finite difference field mapping: auditory evoked fields.

Electric potential maps and magnetic field maps have been used to study brain electrical activity. During the temporal course of an evoked cortical response, the electrical activity of specific neuronal subpopulations change in a sequential manner giving rise to measurable electrical potentials and magnetic fields. For these potentials and fields, both the amplitude and rate of amplitude change have characteristic, time-dependent waveforms. Presently, amplitude waveforms from multiple locations are used to generate magnetic field and electric potential maps which have been found to be useful in understanding the activity of the neurons which give rise to these maps (Romani 1990). This paper introduces a data transformation technique which results in a derived map that we have termed a "finite difference field map" (FDFM). This mapping technique provides information associated with the rate at which the amplitude of the neuronal electric activity changes. In this paper, some advantage of FDFM analysis are illustrated by application of this technique to the study of the auditory evoked cortical field (AECF) N1m waveform. Using data obtained from normal subjects it will be demonstrated that application of the FDFM technique allows the localization of the primary N1m source at an earlier latency than is possible using the conventional waveform data. The source location determined at an early latency by FDFM analysis was identical to that obtained at later from the conventional field data. These data suggest that the primary N1m source is stationary. In addition, analysis of the time sequence of FDFM field maps contains evidence of a second spatially separate source which is co-active with primary N1m source.