Enhancement Of Amplitude Research Articles

Improvement in the signal amplitude and bandwidth of an optical atomic magnetometer via alignment-to-orientation conversion.

We evaluated the alignment-to-orientation conversion (AOC) at the cesium D1 line to improve a nonlinear magneto-optical rotation (NMOR) optical atomic magnetometer's signal amplitude and bandwidth. For the 6 2S1/2 F = 3 → 6 2P1/2 F' = 4 transition, the AOC-related NMOR achieves a 1.7-fold enhancement in signal amplitude compared to the conventional NMOR, benefiting from narrow linewidth and ultraweak power broadening. Therefore, an effective amplitude-to-linewidth ratio is maintained in the high-laser-power region. This method is beneficial for detecting high-frequency magnetic signals in nuclear magnetic resonance and biomagnetism, as the NMOR magnetometer bandwidth increases with laser power.

Hybrid scheme of precoder with μ‐law compander for PAPR reduction and nonlinearity improvement in ADO‐OFDM system

SummaryThe application of orthogonal frequency division multiplexing (OFDM) in a visible light communication (VLC) system increases the peak‐to‐average power ratio (PAPR) of the system. Owing to high PAPR, the intrinsic nonlinearity of LED is an important issue in an asymmetrically clipped DC‐biased optical OFDM (ADO‐OFDM) system. In this paper, a hybrid scheme is proposed to reduce the PAPR as well as to mitigate the nonlinearity in an ADO‐OFDM system. The proposed method is a combination of two ADO‐OFDM formats: precoded ADO‐OFDM and μ‐ADO‐OFDM. The preprocessing of the input using a predetermined matrix (PM) in the precoder relieves the need for a handshake at the receiver. The compression of the peak values and enhancement of low amplitudes of the precoded signal in the time domain yield a low PAPR of 2.4 dB only. Besides PAPR reduction, the union of precoder and compander boosts the bit error rate (BER) performance of the traditional ADO‐OFDM system for μ≤128. The combination of precoder with compander decreases the power requirements for high bit rate transmission for a reference BER of 10−3. In this work, nonlinearity is quantified in terms of error vector magnitude (EVM) in percent. The hybrid scheme shows an EVM of 17.23% for 0 dB input backoff power (IBO) much less than 66.4% EVM for a simple ADO‐OFDM system. In addition to low PAPR and mitigation of nonlinearity, the proposed method shows the improvement in power spectral density (PSD) of the system.

Temperature damping of magneto-intersubband resistance oscillations in magnetically entangled subbands

Magneto-intersubband resistance oscillations (MISO) of highly mobile 2D electrons in symmetric GaAs quantum wells with two populated subbands are studied in magnetic fields tilted from the normal to the 2D electron layer at different temperatures $T$. Decrease of MISO amplitude with temperature increase is observed. At moderate tilts the temperature decrease of MISO amplitude is consistent with decrease of Dingle factor due to reduction of quantum electron lifetime at high temperatures. At large tilts new regime of strong MISO suppression with the temperature is observed. Proposed model relates this suppression to magnetic entanglement between subbands, leading to beating in oscillating density of states. The model yields corresponding temperature damping factor: $A_{MISO}(T)=X/\sinh(X)$, where $X=2\pi^2kT\delta f$ and $\delta f$ is difference frequency of oscillations of density of states in two subbands. This factor is in agreement with experiment. Fermi liquid enhancement of MISO amplitude is observed.

Role of multiple scattering in single particle perturbations in absorbing random media

Speckle patterns produced by disordered scattering systems exhibit a sensitivity to addition of individual particles which can be used for sensing applications. Using a coupled dipole model we investigate how multiple scattering can enhance field perturbations arising in such random scattering based sensors. Three distinct families of multiple scattering paths are shown to contribute and the corresponding complex enhancement factors derived. Probability distributions of individual enhancement factors over the complex plane are characterised numerically within the context of surface plasmon polariton scattering in which absorption is shown to play an important role. We show that enhancements become more strongly dependent on individual scatterer properties when absorption losses are larger, however, amplitude enhancements $\sim 10^2$, comparable to low loss surface plasmons, are achievable through sensor optimisation. Approximate analytic expressions for the complex mean enhancements are also found, which agree well with simulations when loop contributions are negligible.

Study of S‐Wave Microseisms Generated by Storms in the Southeast Australia and North Atlantic

AbstractUsing continuous data from a dense seismic array in Southwestern China, we tracked S‐wave microseism sources generated by two storms in Southeast Australia and the North Atlantic. In the frequency band 0.1–0.2 Hz, the beam strengths for SV‐ and SH‐wave sources can reach 29% and 18% of P‐wave, respectively. We found that the strong SH‐wave is only observed when the seismic sources are near the thick sedimentary regions whereas P‐ and SV‐wave is irrespective of that. It appears that in addition to a three‐dimensional structure that is needed for conversion from P‐wave to SH‐wave, amplitude enhancement by a sedimentary layer is essential for the detection of SH‐wave.

The Role of Cerebral Metabolism in Improving Time Pressured Decisions.

Speed-accuracy tradeoff (SAT) theory dictates that decisions can be made more quickly by sacrificing accuracy. Here we investigate whether the human brain can operate in a brief metabolic overdrive to overcome SAT and successfully make decisions requiring both high levels of speed and accuracy. In the context of BOLD fMRI we expect “a brief metabolic overdrive” to involve an increase in cerebral oxygen metabolism prior to increased cerebral blood flow–a phenomenon known as the “initial dip” which results from a sudden drop in oxyhemoglobin in perfusing blood. Human subjects performed a motion discrimination task consisting of different difficulties while emphasizing either accuracy (i.e., without time pressure) or both speed and accuracy (i.e., with time pressure). Using simultaneous multi-slice fMRI, for very fast (333 ms) measurement of whole brain BOLD activity, revealed two modes of physiological overdrive responses when subjects emphasized both speed and accuracy. The majority of subjects exhibited the hypothesized enhancement of initial dip amplitude in posterior visual cortex (PVC) with the size of the enhancement significantly correlated with improvement in behavioral performance. For these subjects, the traditionally analyzed post-stimulus overshoot was not affected by task emphasis. These results demonstrate the complexity and variability of the BOLD hemodynamic response. The discovered relationships between BOLD response and behavior were only observed when subjects emphasized both speed and accuracy in more difficult trials suggesting that the brain can perform in a state of metabolic overdrive with enhanced neural processing of sensory information specifically in challenging situations.

Spatiotemporal Dynamics of Covert Versus Overt Processing of Happy, Fearful and Sad Facial Expressions.

Behavioral and electrophysiological correlates of the influence of task demands on the processing of happy, sad, and fearful expressions were investigated in a within-subjects study that compared a perceptual distraction condition with task-irrelevant faces (e.g., covert emotion task) to an emotion task-relevant categorization condition (e.g., overt emotion task). A state-of-the-art non-parametric mass univariate analysis method was used to address the limitations of previous studies. Behaviorally, participants responded faster to overtly categorized happy faces and were slower and less accurate to categorize sad and fearful faces; there were no behavioral differences in the covert task. Event-related potential (ERP) responses to the emotional expressions included the N170 (140–180 ms), which was enhanced by emotion irrespective of task, with happy and sad expressions eliciting greater amplitudes than neutral expressions. EPN (200–400 ms) amplitude was modulated by task, with greater voltages in the overt condition, and by emotion, however, there was no interaction of emotion and task. ERP activity was modulated by emotion as a function of task only at a late processing stage, which included the LPP (500–800 ms), with fearful and sad faces showing greater amplitude enhancements than happy faces. This study reveals that affective content does not necessarily require attention in the early stages of face processing, supporting recent evidence that the core and extended parts of the face processing system act in parallel, rather than serially. The role of voluntary attention starts at an intermediate stage, and fully modulates the response to emotional content in the final stage of processing.

Enhancement of Processing Capabilities of Hippocampus Lobe: A P300 Based Event Related Potential Study.

Background and ObjectivesThe influence of music training on different areas of the brain has been extensively researched, but the underlying neurobehavioral mechanisms remain unknown. In the present study, the effects of training for more than three years in Carnatic music (an Indian form of music) on the discrimination ability of different areas of the brain were tested using P300 analysis at three electrode placement sites.Subjects and MethodsA total of 27 individuals, including 13 singers aged 16-30 years (mean±standard deviation, 23±3.2 years) and 14 non-singers aged 16-30 years (mean age, 24±2.9 years), participated in this study. The singers had 3-5 years of formal training experience in Carnatic music. Cortical activities in areas corresponding to attention, discrimination, and memory were tested using P300 analysis, and the tests were performed using the Intelligent Hearing System.ResultsThe mean P300 amplitude of the singers at the Fz electrode placement site (5.64±1.81) was significantly higher than that of the non-singers (3.85±1.60; t(25)=3.3, p<0.05). The amplitude at the Cz electrode placement site in singers (5.90±2.18) was significantly higher than that in non-singers (3.46±1.40; t(25)=3.3, p<0.05). The amplitude at the Pz electrode placement site in singers (4.94±1.89) was significantly higher than that in non-singers (3.57±1.50; t(25)=3.3, p<0.05). Among singers, the mean P300 amplitude was significantly higher in the Cz site than the other placement sites, and among non-singers, the mean P300 amplitude was significantly higher in the Fz site than the other placement sites, i.e., music training facilitated enhancement of the P300 amplitude at the Cz site.ConclusionsThe findings of this study suggest that more than three years of training in Carnatic singing can enhance neural coding to discriminate subtle differences, leading to enhanced discrimination abilities of the brain, mainly in the generation site corresponding to Cz electrode placement.

Discovery of proton hill in the phase space during interactions between ions and electromagnetic ion cyclotron waves

A study using Arase data gives the first observational evidence that the frequency drift of electromagnetic ion cyclotron (EMIC) waves is caused by cyclotron trapping. EMIC emissions play an important role in planetary magnetospheres, causing scattering loss of radiation belt relativistic electrons and energetic protons. EMIC waves frequently show nonlinear signatures that include frequency drift and amplitude enhancements. While nonlinear growth theory has suggested that the frequency change is caused by nonlinear resonant currents owing to cyclotron trapping of the particles, observational evidence for this has been elusive. We survey the wave data observed by Arase from March, 2017 to September 2019, and find the best falling tone emission event, one detected on 11th November, 2017, for the wave particle interaction analysis. Here, we show for the first time direct evidence of the formation of a proton hill in phase space indicating cyclotron trapping. The associated resonance currents and the wave growth of a falling tone EMIC wave are observed coincident with the hill, as theoretically predicted.

Enhancement of Oscillation Amplitude of Cavitation Bubble Due to Acoustic Wake Effect in Multibubble Environment

Acoustic cavitation occurs in ultrasonic treatment causing various phenomena such as chemical synthesis, chemical decomposition and emulsification. Nonlinear oscillations of cavitation bubble are assumed to be responsible for these phenomena. Therefore, bubble oscillations have been studied especially focusing on single bubble system while those in multi-bubble systems have not been analyzed yet despite their importance for the actual ultrasonic processing. In the present study, we numerically investigated the dynamic behavior of cavitation bubbles in multi-bubble systems. The results reveal that the oscillation amplitude of bubbles becomes larger in multi-bubble environment compared with that in the single-bubble case. It is found that this is caused by an acoustic wake effect, which reduces the pressure near a bubble surrounded by other bubbles and increases the time delay between the bubble contraction/expansion cycles and sound pressure oscillations. A new parameter, called “cover ratio” is introduced to quantitatively evaluate the variation in the bubble oscillation amplitude and time delay.

Filter Design and Amplitude Shaping Methodologies for De-Noising Digital Hearing Aids

Uses of the digital hearing aids have been increased in last decades due to heavy noise pollution. The efficiency of the hearing aids is challenging under the presence of highly noisier environments. Therefore, it is highly required to design an efficient de noising method capable of reducing the excessive amplitude present in environment. It is also desirable to design the compact tiny digital herring aids easy to wear. This paper is focused to preset the de-noising methodologies for speech enhancement in digital hearing aids. Various methodologies based on FIR and IIR filter design are presented and performance is evaluated. It is observed that for short term speech samples the amplitude shaping methods become challenging task due to significant amplitude reduction during de-noising. Thus paper presets the adaptive scaling method for amplitude enhancement. The overall goal of paper to design efficient methodology for digital hearing aids.

Observation of planar Hall effect in topological insulator—Bi2Te3

Planar Hall effect (PHE) in topological insulators (TIs) is discussed as an effect that stems mostly from conduction due to topologically protected surface states. Although surface states play a critical role and are of utmost importance in TIs, our present study in Bi2Te3 thin films reflects the need for considering the bulk conduction in understanding the origin of PHE in TIs. This necessity emerges from our observation of an unconventional increase in the PHE signal with TI thickness and temperature where the bulk effect takes over. Here, we find an enhancement in the PHE amplitude by doubling the Bi2Te3 film-thickness on the Si (111) substrate—from ≈ 1.9 nΩ m in 14 quintuple layer (QL) to ≈ 3.1 nΩ m in 30 QL devices at B = 5 T. Also, the PHE amplitude in the 30 QL Bi2Te3 films grown on two different substrates, viz., Si (111) and Al2O3 (0001), shows an increase with temperature. Our experiments indicate that the contribution of bulk states to PHE in TIs could be significant.

Electrophysiological correlates of improved executive function following EEG neurofeedback in adult attention deficit hyperactivity disorder

ObjectiveEvent-related potentials (ERPs) are reported to be altered in relation to cognitive processing deficits in attention deficit hyperactivity disorder (ADHD). However, this evidence is mostly limited to cross-sectional data. The current study utilized neurofeedback (NFB) as a neuromodulatory tool to examine the ERP correlates of attentional and inhibitory processes in adult ADHD using a single-session, within-subject design. MethodsWe recorded high-density EEG in 25 adult ADHD patients and 22 neurotypical controls during a Go/NoGo task, before and after a 30-minute NFB session designed to down-regulate the alpha (8–12 Hz) rhythm. ResultsAt baseline, ADHD patients demonstrated impaired Go/NoGo performance compared to controls, while Go-P3 amplitude inversely correlated with ADHD-associated symptomatology in childhood. Post NFB, task performance improved in both groups, significantly enhancing stimulus detectability (d-prime) and reducing reaction time variability, while increasing N1 and P3 ERP component amplitudes. Specifically for ADHD patients, the pre-to-post enhancement in Go-P3 amplitude correlated with measures of improved executive function, i.e., enhanced d-prime, reduced omission errors and reduced reaction time variability. ConclusionsA single-session of alpha down-regulation NFB was able to reverse the abnormal neurocognitive signatures of adult ADHD during a Go/NoGo task. SignificanceThe study demonstrates for the first time the beneficial neurobehavioral effect of a single NFB session in adult ADHD, and reinforces the notion that ERPs could serve as useful diagnostic/prognostic markers of executive dysfunction.

Surface plasmon enhanced THz emission with nanoporous gold supported CdTe.

Terahertz emission by ultrafast excitation of semiconductor/metal interfaces was found strongly enhanced by plasmon resonance. Here, a three-dimensional nanoporous gold (NPG) was used to form semiconductor/metal compound with cadmium telluride (CdTe). We investigated the specific impact of surface plasmon from randomly nanoporous structure in the ultrafast optoelectronic response for THz generation, and observed a THz amplitude enhancement around an order of magnitude from CdTe on NPG compared to that from CdTe on silicon. Moreover, the plasmon enhancement for THz emission from NPG is stronger than that from gold film, indicating that randomly nanoporous structure is also effective for plasmonic enhancement in THz band.

Dexterous manual movement facilitates information processing in the primary somatosensory cortex: A magnetoencephalographic study.

The interaction between the somatosensory and motor systems is important for control of movement in humans. Cortical activity related to somatosensory response and sensory perception is modulated by the influence of movement executing mechanisms. This phenomenon has been observed as inhibition in the short‐latency components of somatosensory evoked potentials and magnetic fields (SEPs/SEFs). Although finger is the most dexterous among all the body parts, the sensorimotor integration underlying this dexterity has not yet been elucidated. The purpose of this study was to examine the sensorimotor integration mechanisms in the primary somatosensory cortex (SI) during simple and complicated finger movement. The participant performed tasks that involved picking up a wooden block (PM task) and picking up and turning the wooden block 180° (PTM task) using the right‐hand fingers. During these tasks, the SEFs following right median nerve stimulation were recorded using magnetoencephalography. The amplitude of the M20 and M30 components showed a significant reduction during both manual tasks compared to the stationary task, whereas the M38 component showed a significant enhancement in amplitude. Furthermore, the SEFs recorded during continuous rotation of the block (rotation task) revealed a characteristic pattern of SI activity that was first suppressed and then facilitated. Since this facilitation is noticeable during complicated movement of the fingers, this phenomenon is thought to underlie a neural mechanism related to finger dexterity.

Yielding and resolidification of colloidal gels under constant stress

We examine the macroscopic deformation of a colloidal depletion gel subjected to a step shear stress. Three regimes are identified depending on the magnitude of the applied stress: (i) for stresses below yield stress, the gel undergoes a weak creep in which the bulk deformation grows sublinearly with time similar to crystalline and amorphous solids. For stresses above yield stress, when the bulk deformation exceeds approximately the attraction range, the sublinear increase of deformation turns into a superlinear growth which signals the onset of non-linear rearrangements and yielding of the gel. However, the long-time creep after such superlinear growth shows two distinct behaviors: (ii) under strong stresses, a viscous flow is reached in which the strain increases linearly with time. This indicates a complete yielding and flow of the gel. In stark contrast, (iii) for weak stresses, the gel after yielding starts to resolidify. More homogenous gels that are produced through enhancement of either interparticle attraction strength or strain amplitude of the oscillatory preshear, resolidify gradually. In contrast, in gels that are more heterogeneous resolidification occurs abruptly. We also find that heterogenous gels produced by oscillatory preshear at intermediate strain amplitude yield in a two-step process. Finally, the characteristic time for the onset of delayed yielding is found to follow a two-step decrease with increasing stress. This is comprised of an exponential decrease at low stresses, during which bond reformation is decisive and resolidification is detected, and a power law decrease at higher stresses where bond breaking and particle rearrangements dominate.

Capacitive Boosted Ring Oscillators for All-Digital Phase-Locked Loops (ADPLLs)

Ring oscillator (RO)-based digital phase-locked loops (DPLLs) are very attractive for system-on-chip applications due to their tuning range, good phase noise property but suffer from compactness and power requirements. In this work, the concept of capacitive boosting as one of the key solutions which enhances the amplitude of oscillations of the RO is proposed, making it a suitable solution to the biomedical applications, specifically for medical implant communication system (MICS) band of operation ranging from 400[Formula: see text]MHz to 405[Formula: see text]MHz. With coarse and fine-tuning blocks, this digitally controlled oscillator (DCO) promises a good resolution. The coarse tuning is achieved using conventional MOS capacitors and the fine-tuning is achieved by controlling the fractional metal oxide semiconductor (MOS) capacitances. To benchmark the performance metrics of the single-stage RO in this work, simulations were performed for 680[Formula: see text]mV supply voltage in 45[Formula: see text]nm complementary metal oxide semiconductor (CMOS) technology. The output varies in the range from [Formula: see text]0.422[Formula: see text]V to [Formula: see text][Formula: see text]V, indicating about 224% amplitude enhancement. Despite process voltage temperature (PVT) variations, we can see little impact on the boosted output levels. The designed DCO operates up to a maximum frequency of 495[Formula: see text]MHz at 0.68[Formula: see text]V. The proposed RO has lesser power consumption than any conventional RO, operating at a center frequency of 402[Formula: see text]MHz, thus making it better suitable for the MICS band of applications. Phase noise of [Formula: see text][Formula: see text]dBc/Hz at an offset of 200[Formula: see text]kHz was obtained. The proposed differential DCO consumed power was 95.26[Formula: see text][Formula: see text]W. The figure of merit (FoM) for this DCO is [Formula: see text] (dBc/Hz). The area consumed by the DCO is 0.01872[Formula: see text]mm2.

Medial Olivocochlear Reflex Effect on Cochlear Response in Humans: Elicitor Side and Level.

Understanding the functional differences between crossed and uncrossed medial olivocochlear (MOC) neurons has been of interest to researchers for decades. Previous reports revealed conflicting results about which MOC pathway, crossed or uncrossed, is stronger in humans. Both crossed and uncrossed MOC neurons synapse at the base of the outer hair cells (OHCs) in each ear. OHCs generate the cochlear microphonic, which is a major contributor to the cochlear response (CR) PURPOSE: The current study investigated the effects of eliciting the crossed and uncrossed MOC reflex (MOCR) on CR in humans with three levels of noise. Normal-hearing, young adults (n = 16) participated in this study. The CR was recorded using 500 Hz tone-burst stimuli presented at 80 dB nHL. To examine the crossed and uncrossed MOCR, CR was recorded without and with continuous ipsilateral or contralateral broadband noise (BBN) at three levels (40, 50, and 60 dB SPL). Analysis of the CR was completed using the amplitude of the response extracted using fast Fourier transform. Statistical analysis was completed using repeated measures analysis of variance and post-hoc analysis. Compared with baseline, the presentation of BBN, specifically contralaterally, resulted in CR enhancement with no significant difference as a function of the three BBN levels. Greater enhancement of the CR amplitude was observed with contralateral than ipsilateral BBN elicitor. The current findings suggest that a contralateral elicitor of the uncrossed MOC pathway results in a larger CR amplitude enhancement compared with an ipsilateral elicitor of the crossed MOC pathway, regardless of the elicitor level. Eliciting the MOCR appears to modulate the OHCs function. Furthermore, assessing the MOCR with the 500 Hz CR with BBN elicitors at moderate levels should separate its effects (i.e., increase response amplitude) from those associated with the middle ear muscle reflex (i.e., reduce response amplitude).

Subsurface structural mapping from high-resolution gravity data using advanced processing methods

The study area has a complex geological structure and is studied for mapping the density interfaces using geophysical techniques. However, it has not been studied for mapping geological structures, such as contacts and faults that appear as lineaments in gravity data. In this study, the lineaments in the area have been delineated using Bouguer gravity anomaly data, though some modern processing methods, such as horizontal gradient amplitude (HGA), tilt angle of horizontal gradient amplitude (THGA), and enhancement of horizontal gradient amplitude (EHGA). Most of the identified lineaments are trending in the NW–SE direction and some WE-trending lineaments in the southeastern region. This study provides new information for a better understanding of the structural framework and tectonic setting of the Thua Thien Hue area.

Nonlinear periodic structures in a magnetized plasma with Cairns distributed electrons

The electrostatic ion acoustic (IA) nonlinear periodic (cnoidal) waves are studied in a magnetized plasma comprising of cold ions and Cairns distributed electrons. By employing reductive perturbation technique (RPT), the nonlinear Korteweg-de Vries (KdV) and modified KdV (mKdV) equations are derived, and their cnoidal wave (CW) solutions are obtained. For a given set of plasma parameters, the present model supports both compressive and rarefactive nonlinear periodic structures. In the present work, the effects of plasma parameters like nonthermality of electrons ( $$\beta $$ ) and obliqueness ( $$ l_{z} $$ ) are investigated. It is found that increasing values of $$\beta $$ and $$l_{z}$$ lead to enhancement (reduction) in amplitude of IA compressive (rarefactive) nonlinear periodic structures. Our present study has some relevance to the CW structures observed in magnetosphere via POLAR and FAST spacecrafts.