Changes In Spectral Content Research Articles

The impact of light adjustment versus tuneable white mode on ICU staff’s circadian rhythms

ABSTRACT The significance of lighting design in intensive care units (ICUs) for healthcare professionals’ demanding work and its profound impact on health, visual comfort and overall well-being cannot be overstated. This study investigates the potential of controlling luminous flux and spectral characteristics to enhance ICU lighting environments. It aims to determine whether modifying the lighting spectrum positively affects health without compromising visual comfort and colour discrimination. Two distinct LED lighting configurations were tested. The first adjusted only light levels, providing insights into staff responses. The second used tuneable white lighting, allowing changes in spectral content and colour temperature throughout shifts, resembling natural light variations. Effects were assessed via subjective perception surveys and objective colour rendering tests. Physiological impacts were evaluated through urine and blood samples, analysing melatonin suppression and cortisol levels, crucial for regulating rhythms and stress. Results offer valuable insights into lighting’s impact on ICU occupants’ well-being, highlighting the potential benefits of spectral adjustments while maintaining visual comfort and colour discrimination. This holistic approach to lighting design in critical care settings emphasizes the importance of balancing health benefits with lighting quality.

Cortical and Subthalamic Nucleus Spectral Changes During Limb Movements in Parkinson's Disease Patients with and Without Dystonia.

ABSTRACTBackgroundDystonia is an understudied motor feature of Parkinson's disease (PD). Although considerable efforts have focused on brain oscillations related to the cardinal symptoms of PD, whether dystonia is associated with specific electrophysiological features is unclear.ObjectiveThe objective of this study was to investigate subcortical and cortical field potentials at rest and during contralateral hand and foot movements in patients with PD with and without dystonia.MethodsWe examined the prevalence and distribution of dystonia in patients with PD undergoing deep brain stimulation surgery. During surgery, we recorded intracranial electrophysiology from the motor cortex and directional electrodes in the subthalamic nucleus (STN) both at rest and during self‐paced repetitive contralateral hand and foot movements. Wavelet transforms and mixed models characterized changes in spectral content in patients with and without dystonia.ResultsDystonia was highly prevalent at enrollment (61%) and occurred most commonly in the foot. Regardless of dystonia status, cortical recordings display beta (13–30 Hz) desynchronization during movements versus rest, while STN signals show increased power in low frequencies (6.0 ± 3.3 and 4.2 ± 2.9 Hz peak frequencies for hand and foot movements, respectively). Patients with PD with dystonia during deep brain stimulation surgery displayed greater M1 beta power at rest and STN low‐frequency power during movements versus those without dystonia.ConclusionsSpectral power in motor cortex and STN field potentials differs markedly during repetitive limb movements, with cortical beta desynchronization and subcortical low‐frequency synchronization, especially in patients with PD with dystonia. Greater knowledge on field potential dynamics in human motor circuits can inform dystonia pathophysiology in PD and guide novel approaches to therapy. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society

Recursive Algorithms for Computing Sliding DCT With Arbitrary Step

Discrete cosine transform (DCT) is one of the most popular transforms in digital signal processing. Its close approximation to the Karhunen-Loeve transform implies a high degree of energy compaction. Therefore, it can be used in a wide range of applications such as sensor noise removal, spectral analysis, linear filtering, feature extraction and pattern recognition. When it is required to estimate the spectrum of a nonstationary process such as radar, speech, biomedical and communication signals, a short-time (sliding) transform can be used. Basically, the sliding transform means that the transform is calculated on a fixed-length window of the signal, which is constantly updated with new samples while the oldest ones are discarded. In some engineering applications, when the spectral content changes slowly, the window can slide more than one sample at a time to speed up the spectral analysis. In this paper, second-order recursive algorithms are proposed for fast computing the DCT in windows that are located at a given equal distance from each other. The computational complexity of the algorithms is compared with that of common fast and sliding DCT algorithms.

Do we need two ears to perceive the distance of a virtual frontal sound source?

The present study investigated whether the perception of virtual auditory distance is binaural, monaural, or both. Listeners evaluated the distance of a frontal source of pink noise simulated in a room via headphones. Experiment 1 was performed with eyes closed in a soundproof booth. Experiment 2 was performed with eyes open in the room used to create the stimuli. Individualized and non-individualized stimuli were compared. Different conditions for controlling sound level were tested. The amount of binaural information in the stimuli was varied by mixing the left and right ear signals in different proportions. Results showed that the use of non-individualized stimuli did not impair distance perception. Binaural information was not used by naive listeners to evaluate distance, both with and without visual information available. However, for some listeners, a complete absence of binaural information could disrupt distance evaluation with headphones. Sound level was a dominant cue used by listeners to judge for distance, and some listeners could also reliably use reverberation-related changes in spectral content. In the absence of specific training, artificial manipulation of sound level greatly altered distance judgments.

Wear mechanisms alteration at braking interface through atmosphere modification

This paper relates to changes in the third body arrangement of a squealing pad-disc interface, triggered by altering the tribological circuit of particles. A sealed chamber placed around a friction experiment, allows to run-in the parts with dry air atmosphere, and then to switch from air to argon. Observations of surfaces worn in dry air match the literature. The major part of the surfaces is covered by a third-body layer containing oxidized metal, in the form of powder or compacted plateaus, the rest of the surfaces being native, non-oxidized material from the first bodies. The squealing sound is steady and has a well-defined spectral content. Two stages of sliding of 400 s each are then performed with changed atmosphere. The squealing sound becomes sporadic and its spectral content changes. On the pad's surface, the coverage of compacted third-body plateaus reduces, while more non-oxidized metal appears. A specific pattern of plateaus appears on top of graphite particles. The evolution of the vibrational behavior and of the third-body layer are both gradual and have not reached a steady state when the experiment is stopped. We propose a scenario involving a change in the balance between the source flows and the wear flow as an explanation of the observed tribological changes.

Measurement of attentional reserve and mental effort for cognitive workload assessment under various task demands during dual-task walking

Previous work focused on cognitive workload assessment suggests EEG spectral content and component amplitudes of the event-related potential (ERP) waveform may index mental effort and attentional reserve, respectively. Although few studies have assessed attentional reserve and mental effort during upper-extremity performance, none have employed a combined approach to measure cognitive workload during locomotion. Therefore, by systematically considering ERPs, spectral content and importantly their combination, this study aimed to examine whether concurrent changes in spectral content and ERPs could collectively serve as an index of cognitive workload during locomotion. Specifically, ERP and EEG biomarkers were assessed as participants performed a cognitive task under two levels of difficulty (easy or hard) and two conditions (seated or walking). Changes in attentional reserve and mental effort appeared to collectively index cognitive workload under varying demands due to changes in task difficulty or performance conditions. This work can inform cognitive workload assessment in patient populations with gait deficiencies for future applications.

Predicting the spectral effects of soils on high concentrating photovoltaic systems

Soiling losses on high concentrating photovoltaic (HCPV) systems may be influenced by the spectral properties of accumulated soil. We have predicted the response of an isotype cell to changes in spectral content and reduction in transmission due to soiling using measured UV/vis transmittance through soil films. Artificial soil test blends deposited on glass coupons were used to supply the transmission data, which was then used to calculate the effect on model spectra. The wavelength transparency of the test soil was varied by incorporating red and yellow mineral pigments into graded sand. The more spectrally responsive (yellow) soils were predicted to alter the current balance between the top and middle subcells throughout a range of air masses corresponding to daily and seasonal variation.

From the STFT to the Wigner Distribution [Lecture Notes

The analysis, processing, and parameters estimation of signals whose spectral content changes in time are of crucial interest in many applications, including radar, acoustics, biomedicine, communications, multimedia, seismic, and the car industry [1]-[11]. Various signal representations have been introduced to deal with this kind of signals within the area known as time-frequency (TF) signal analysis. The oldest analysis tool in this area is the short-time Fourier transform (STFT), as a direct extension of the classical Fourier analysis. The other key tool is the Wigner distribution (WD), introduced in signal analysis from quantum mechanics. The aim of this lecture note is to present and relate these two of the most important tools in the TF signal analysis, the STFT and the WD (introduced by two Nobel prize winners, D. Gabor and E. Wigner, respectively). This relation is a basis for the S-method (SM), an efficient and simple TF signal analysis tool providing a gradual transition between these two representations.

Synchrotron far-infrared spectroscopy of corroded steel surfaces using a variable angle of incidence.

Far-infrared spectroscopy, using a synchrotron source, has been used to study carbon steel corroded in CO2-saturated brine in the presence and absence of the corrosion inhibitor 2-mercaptopyrimidine (MPY), which allowed the steel surface roughness to be modified. The effect of the angle of incidence (θi, 30-80°) on the band intensity and observed bands of the spectra from these surfaces has been determined. For the MPY-treated steel (low surface roughness) the highest band intensity is observed at high θi (80°) and different bands were observed at different θi. In contrast, for the MPY-free steel (high surface roughness) the highest band intensity is observed at low θi (30°) and spectral content changes were not observed. The results are explained in terms of the roughness of the MPY-treated and MPY-free steels, and their effect on the level of diffusely reflected light of the incident infrared beam.

Removing ECG contamination from EMG recordings: A comparison of ICA-based and other filtering procedures

Trunk muscle electromyography (EMG) is often contaminated by the electrocardiogram (ECG), which hampers data analysis and potentially yields misinterpretations. We propose the use of independent component analysis (ICA) for removing ECG contamination and compared it with other procedures previously developed to decontaminate EMG. To mimic realistic contamination while having uncontaminated reference signals, we employed EMG recordings from peripheral muscles with different activation patterns and superimposed distinct ECG signals that were recorded during rest at conventional locations for trunk muscle EMG. ICA decomposition was performed with and without a separately collected ECG signal as part of the data set and contaminated ICA modes representing ECG were identified automatically. Root mean squared relative errors and correlations between the linear envelopes of uncontaminated and contaminated EMG were calculated to assess filtering effects on EMG amplitude. Changes in spectral content were quantified via mean power frequencies. ICA-based filtering largely preserved the EMG’s spectral content. Performance on amplitude measures was especially successful when a separate ECG recording was included. That is, the ICA-based filtering can produce excellent results when EMG and ECG are indeed statistically independent and when mode selection is flexibly adjusted to the data set under study.

System for magnetic monitoring of high voltage motors MM6212

This paper suggests the possibility of diagnosing different types of failure in working induction motors using a device for spectral analysis of axial leakage flux, which has been developed by the Electrotechnical Institute Nikola Tesla. A search coil, which can be of different diameters, was mounted concentrically on the shaft at the rear of the motor. The electromotive force (emf) on each of the coils, created as a result of weak magnetic field changes, has a low amplitude. Following the necessary amplifications and adjustments, the signal is digitised on acquisition. In the fast Fourier transform (FFT) stage, the sampled and quantised digital time-based signal is converted to a frequency spectrum. Changes in spectral content are used to identify developing faults.

Tissue Dynamics Spectroscopy for Three-Dimensional Tissue-Based Drug Screening

Tissue dynamics spectroscopy combines dynamic light scattering with short-coherence digital holography to capture intracellular motion inside multicellular tumor spheroid tissue models. The cellular mechanical activity becomes an endogenous imaging contrast agent for motility contrast imaging. Fluctuation spectroscopy is performed on dynamic speckle from the proliferating shell and hypoxic core to generate drug-response spectrograms that are frequency versus time representations of the changes in spectral content induced by an applied compound or an environmental perturbation. A combination of 28 reference compounds and conditions applied to rat osteogenic UMR-106 spheroids generated spectrograms that were crosscorrelated in a similarity matrix used for unsupervised hierarchical clustering of similar compound responses. This work establishes the feasibility of tissue dynamics spectroscopy for three-dimensional tissue-based phenotypic profiling of drug response as a fully endogenous probe of the response of tissue to reference compounds.

Sample Entropy Tracks Changes in Electroencephalogram Power Spectrum With Sleep State and Aging

The regularity of electroencephalogram signals was compared between middle-aged (47.2 +/- 2.0 years) and elderly (78.4 +/- 3.8 years) female subjects in wake, nonrapid eye movement stages 2 and 3 (S-2, S-3), and rapid eye movement sleep. Signals from C3A2 leads of healthy subjects, acquired from polysomnograms obtained from the Sleep Heart Health Study, were analyzed using both sample entropy (SaEn) and power spectral analysis (delta, theta, alpha, and beta frequency band powers). SaEn changed systematically and significantly (P < 0.001) with sleep state in both age groups, following the relationships wake > rapid eye movement > S-2 > S-3. SaEn was found to be negatively correlated with delta power and positively correlated with beta power. Small changes in SaEn seem to reflect changes in spectral content rather than changes in regularity of the signal. A better predictor of SaEn than the frequency band powers was the logarithm of the power ratio (alpha + beta)/(delta + theta). Thus, SaEn seems to reflect the balance between sleep-promoting and alertness-promoting mechanisms. SaEn of the elderly was larger than that of middle-aged subjects in S-2 (P = 0.029) and rapid eye movement (P = 0.001), suggesting that cortical state is shifted toward alertness in elderly subjects in these sleep states compared with the middle-aged subjects.

Complexity of treatment decisions with older patients: who, when and what to treat?

<h3>ABSTRACT</h3> <h3>Background</h3> Dystonia is an under-studied motor feature of Parkinson disease (PD). Although considerable efforts have focused on brain oscillations related to the cardinal symptoms of PD, whether dystonia is associated with specific electrophysiological features is unclear. <h3>Objectives</h3> To investigate subcortical and cortical field potentials at rest and during contralateral hand and foot movements in PD patients with and without dystonia. <h3>Methods</h3> We examined the prevalence and distribution of dystonia in PD patients undergoing deep brain stimulation surgery and recorded intracranial electrophysiology from motor cortex and directional electrodes in subthalamic nucleus (STN) both at rest and during self-paced repetitive contralateral hand and foot movements. Wavelet transforms and mixed models characterized changes in spectral content in patients with and without dystonia. <h3>Results</h3> Dystonia was highly prevalent at enrollment (61%) and occurred most commonly in the foot. Regardless of dystonia status, cortical recordings display beta (13-30 Hz) desynchronization during movements versus rest, while STN signals show increased power in low frequencies (6.0±3.3 and 4.2±2.9 Hz peak frequencies for hand and foot movements respectively). PD patients with dystonia during DBS surgery displayed greater M1 beta power at rest and STN low frequency power during movements versus those without dystonia. <h3>Conclusions</h3> Spectral power in motor cortex and STN field potentials differs markedly during repetitive limb movements, with cortical beta desynchronization and subcortical low frequency synchronization, especially in PD patients with dystonia. Greater knowledge on field potential dynamics in human motor circuits can inform dystonia pathophysiology in PD and guide novel approaches to therapy.

Sensitive Chemical Optic Sensor Using Birefringent Porous Glass for the Detection of Volatile Organic Compounds

A simple design involving a birefringent porous glass oriented between two crossed polarizers serves as the foundation for an optically based sensitive broad-spectrum chemical sensor. Volatile organic compounds (VOCs) such as acetonitrile vapors can be readily detected at concentrations of as low as 50 ppm. Changes are observed in polarized light transmitted by the anisotropic porous material constituting the sensor, upon exposure to VOC-bearing air, as intensity changes at a defined wavelength or as changes in spectral content (color) detectable by the eye. The optical effects resulting from exposure to various vapors are reversible and may result from adsorption of solvent vapors with attendant reduction of anisotropy. The microporous structure as well as the surface chemistry of the sensor may be controlled for tuning the response to VOCs for industrial applications. Miniaturization of the sensor using low-cost materials such as plastic or glass optical fibers, Polaroid films, and birefringent porous glass is demonstrated. The sensor described in this paper could use ambient light as source and the eye as detector (color change) or electronically controlled light emission and detection for better sensitivity and real time monitoring of VOCs. Such intrinsic explosion proof sensors could be used to safely monitor VOC levels in remote environments.

Temporal and spectral properties of voiceless fricatives in aphasia and apraxia of speech

Background: This study represents an extension of a previous examination of fricative production in aphasic speakers with and without apraxia of speech (AOS; Haley, Ohde, & Wertz, 2000a). In our previous work, spectral overlap was found between alveolar and palatal voiceless fricatives produced by aphasic speakers with and without AOS, but not in normal speakers. Because all spectral measures were obtained at the midpoint of the fricative segment, categorical overlap may have been exaggerated by intra-segmental changes from one place of articulation to another. Moreover, the duration of the segments and the interaction between temporal and spectral properties were not examined. Aims: We asked three questions: (1) Are fricative segments longer than normal in aphasic speakers with and without AOS? (2) Are patterns of spectral overlap between places of articulation comparable at the beginning, middle, and end of the fricative segment? (3) What is the spectral evidence regarding intra-segmental changes in place of articulation? Methods & Procedures: The speech sample was the same as in our original investigation. Thus, 10 aphasic speakers with AOS, 10 aphasic speakers without AOS, and 10 normal control speakers each produced 48 words with an initial voiceless sibilant fricative. The duration of the fricative segment was measured and the Bark-transformed first spectral moment (FSM) time histories were computed for each utterance. Both quantitative and qualitative procedures were used to examine the data. Outcomes & Results: Fricative segment duration was significantly longer for speakers with coexisting aphasia and AOS than for the normal control group. Visual inspection of first spectral moment time histories revealed intra-segmental changes in spectral content for individual speakers in all three groups. The pattern of change across repeated productions was more variable for aphasic speakers with and without AOS than for normal speakers. Several individual patterns of spectral change were observed among aphasic and apraxic speakers. Spectral overlap between [s] and [] was noted in aphasic speakers with and without AOS at the beginning, middle, and end of the fricative segment, whereas normal speakers demonstrated limited overlap only at segment onset and offset. Conclusions: There was no evidence that intra-segmental modifications in place of articulation accounted for our previous observation of spectral overlap between fricative targets. The results indicate that abnormal phonetic properties are associated with, but not restricted to, a diagnosis of AOS.

Neurotolerability of gadobenate dimeglumine in a rat model of focal brain ischemia: EEG evaluation.

The neurologic pathologies for which contrast-enhanced MRI is indicated are often accompanied by a disruption of the blood-brain barrier (BBB), which allows the contrast agent to come into contact with the nervous tissue. Thus, assessment of the neurologic safety for a new contrast agent is of crucial importance. The objective of this study was to assess the neurotolerability of the new MRI contrast agent gadobenate dimeglumine using EEG in the presence of focal lesions of the BBB. Lesions of the BBB were obtained inducing a photochemical ischemia in rats. Gadobenate dimeglumine was intravenously administered at 4.0 mmol/kg. An EEG was recorded during sleep/awake behavior and was analyzed for pathologic tracing and for changes in spectral content in terms of total power and frequency index. The presence of the BBB lesions was verified using high-performance liquid chromatography measurement of the gadobenate ion content in the brain. Gadobenate dimeglumine did not have any epileptogenic effect in ischemic rats. However, it caused a transitory shift of the EEG power spectrum toward the 0.5 to 9 Hz frequency bands of the lesioned hemisphere during quiet wake. In the lesioned cortex, higher levels of gadobenate ion were found until 3 hours after administration. In experimental conditions of focal brain ischemia associated with BBB lesions, gadobenate dimeglumine was well tolerated up to doses even 10 times higher than the maximum clinical dose (0.3 mmol/kg) intended for brain imaging procedures.

Fourier Transform Infrared Spectroscopy as a Powerful Tool for the Study of Carbohydrates in Aqueous Solutions

FT-IR spectral investigations on carbohydrates were undertaken in aqueous media in order to facilitate the assignments of vibrational bands. For pure anomeric forms of glucose, FT-IR spectra obtained as a function of time revealed many changes in spectral content, providing new information about anomer characteristic bands in aqueous media. It was also found that fructose, which is known to undergo complex mutarotation, exhibits two types of spectral changes, whereas glucose, which undergoes simple mutarotation, shows a single type of spectral change. Thus FT-IR spectral investigations in aqueous carbohydrates should be able to distinguish between simple and complex mutarotation cases. As a vibrational spectroscopic technique, the importance of FT-IR spectroscopy is further emphasized by showing that Raman spectroscopy is not sensitive enough to reveal the structural changes of carbohydrates in aqueous media.

Jet noise spectra at low Reynolds number

The current interest in coherent structures in turbulent flows and their possible influence on acoustic radiation is the impetus for a detailed examination of the acoustic field surrounding a turbulent jet at low Reynolds numbers. In this study the acoustic characteristics are examined over a Reynolds number range of 16 000 to 148 000 at a constant Mach number of 0.52. This is accomplished using a series of geometrically similar nozzles ranging in size from 1.3 to 12.2 mm. The remarkable conclusion is that the spectral content changes significantly below a Reynolds number of about 1 × 105. The shift in peak frequency with increasing emission angle (the so‐called reverse Doppler shift) characteristic of high Reynolds number jets is not observed. In fact, the spectra are observed to peak at a Helmholtz number, fd/ɑ0, of about 0.08, independent of emission angle. This result is discussed in light of recent findings concerning the role of initial shear layer instabilities on the subsequent development of turbulent flow. [Work supported by AFOSR.]

Study of Self-Focusing and Self-Phase-Modulation in the Picosecond-Time Regime

The propagation properties of a single picosecond pulse produced by a mode-locked Nd:glass laser are studied in several liquids by observing the optically induced birefringence and the changes in spectral content of the self-focused light. The spatial properties of the focal volume are studied using multiple second-harmonic (SH) probing beams which measure the induced birefringence from a single infrared pulse sequentially in many parts of the cell. These data allow a direct determination of the velocity of propagation of the high-intensity region. The formation and disappearance of high-intensity regions is also observed, as well as propagation lengths greater than 4 cm on a single pulse for the case of C${\mathrm{S}}_{2}$. Using temporally compressed SH pulses, we find that the induced birefringence is due primarily to the orientational Kerr effect in materials such as nitrobenzene and toluene. Results in C${\mathrm{S}}_{2}$ are also consistent with this mechanism and indicate that the duration of the infrared pulse in the focal volume is less than the duration of the incident pulse. The propagation properties of filaments which pass through a 1-mm glass slide are investigated, and the properties of beams which are focused within the cell by an external lens are studied. The occasional appearance of multiple filaments on some laser shots at different temporal positions in the pulse indicates the possibility of using this technique for beam wave-front diagnostics. The experimental spectra of the self-focused light were studied using beams of picosecond pulses in a number of materials, and they are all similar, showing a symmetric broadening about the laser frequency. The spectra are modulated with an interference structure which is characteristic of a phase-modulated pulse. The effective duration of the modulated pulse is consistent with the duration of the pulse in the high-intensity region as determined from the propagation data. Most of the results of the propagation and frequency-broadening experiments can be explained with a transient theory of self-focusing which results from numerical integration of the self-focusing equations with a relaxing nonlinear index. The theory, however, predicts an asymmetric frequency broadening, and therefore additional mechanisms are discussed which may account for the large amount of upshifted light which was observed.