Low Spectral Frequencies Research Articles

Infrared spectra of soil organic matter under a primary vegetation sequence

BackgroundWe applied Fourier-Transformed Infrared Spectroscopy (FTIR) techniques in combination with selective humus extractions to investigate in situ the chemical features of organic matter in three soil profiles recently developed from Dutch sand dunes, under well-documented vegetation sequence and containing a relatively simple mineral-organic matter system. Water-soluble and alkaline-soluble extracts were also studied to match the changes of humus in the soil residues.ResultsDiffuse Reflectance Infrared Fourier Transform (DRIFT) and transmission spectra differed in resolution and sensitivity. DRIFT was superior in revealing structural information on the organic matter present in the soil samples whereas transmission spectra showed higher resolution for the bands of inorganic material at lower spectral frequencies. Differences between H and B horizons were due to the amount of hydrophilic organic acids, partly unsaturated, that were extracted by alkali. Extractable carboxylic acids and other hydrophilic compounds such as peptides and carbohydrates were larger in the less developed soils under pine and crowberry than in the more advanced profiles under beech. Humin residues from both H and B horizons retained unextractable aliphatic components and carboxylic groups involved in strong complexes with minerals, thereby confirming other findings that showed the largely aliphatic character of the unextractable humic fraction. Accumulation of poorly-soluble organic materials in these soils occur by protection from biodegradation due both to complexation with soil minerals and to a process by which apolar humic constituents form a separate hydrophobic phase where no biological activity can take place. Transport of poorly soluble compounds from H to B horizons, noticed especially in the more developed profiles, may have occurred through humic aggregates containing hydrophobic phases.ConclusionsThis work shows that the DRIFT technique in combination with soil chemical treatments can be suitably employed to investigate the changes of organic matter in whole soil samples and represents a valid tool to investigate the role of organic matter in soil profile development.

Glyph guessing for 'oo' and 'ee': spatial frequency information in sound symbolic matching for ancient and unfamiliar scripts.

In three experiments, we asked whether diverse scripts contain interpretable information about the speech sounds they represent. When presented with a pair of unfamiliar letters, adult readers correctly guess which is /i/ (the ‘ee’ sound in ‘feet’), and which is /u/ (the ‘oo’ sound in ‘shoe’) at rates higher than expected by chance, as shown in a large sample of Singaporean university students (Experiment 1) and replicated in a larger sample of international Internet users (Experiment 2). To uncover what properties of the letters contribute to different scripts' ‘guessability,’ we analysed the visual spatial frequencies in each letter (Experiment 3). We predicted that the lower spectral frequencies in the formants of the vowel /u/ would pattern with lower spatial frequencies in the corresponding letters. Instead, we found that across all spatial frequencies, the letter with more black/white cycles (i.e. more ink) was more likely to be guessed as /u/, and the larger the difference between the glyphs in a pair, the higher the script's guessability. We propose that diverse groups of humans across historical time and geographical space tend to employ similar iconic strategies for representing speech in visual form, and provide norms for letter pairs from 56 diverse scripts.

Frequency-noise cancellation in optomechanical systems for ponderomotive squeezing

Ponderomotive squeezing of the output light of an optical cavity has been recently observed in the MHz range in two different cavity optomechanical devices. Quadrature squeezing becomes particularly useful at lower spectral frequencies, for example in gravitational wave interferometers, despite being more sensitive to excess phase and frequency noise. Here we show a phase/frequency noise cancellation mechanism due to destructive interference which can facilitate the production of ponderomotive squeezing in the kHz range and we demonstrate it experimentally in an optomechanical system formed by a Fabry-P\'{e}rot cavity with a micro-mechanical mirror.

Lateralization produced by interaural temporal and intensitive disparities of high-frequency, raised-sine stimuli: Data and modeling

An acoustic pointing task was used to measure extents of laterality produced by combinations of ongoing envelope-based interaural temporal disparities (ITDs) and interaural intensitive disparities (IIDs) of 4-kHz-centered raised-sine stimuli [Bernstein and Trahiotis, J. Acoust. Soc. Am. 125, 3234-3242 (2009),] while varying, parametrically, their peakedness, depth of modulation, and frequency of modulation. The study was designed to assess whether IIDs act as "weights" within the putative "binaural display" at high spectral frequencies (where the envelopes convey ITD-information) as appears to be the case at low spectral frequencies (where the waveforms, i.e., fine-structure and envelopes, convey ITD-information). The data indicate that envelope-based IIDs do principally act as weights and that they appear to exert their influence on lateral position independently of the influence of ITDs. Quantitative analyses revealed that an augmented form of the cross-correlation-based "position-variable" model of Stern and Shear [J. Acoust. Soc. Am. 100, 2278-2288 (1996)] accounted for 94% of the variance in the data. This success notwithstanding, for a small subset of the data, predictions could be improved by assuming that the listeners utilized information within auditory filters having center frequencies above 4 kHz.

Empirical and theoretical findings concerning how interaural intensitive disparities affect lateralization for high- versus low -frequency stimuli.

This presentation concerns empirical and theoretical findings concerning the potency of interaural intensitive disparities (IIDs) at low versus high spectral frequencies. In one context, an acoustic pointing task was used to measure how IIDs affect extents of laterality. Laterality was measured for 4-kHz-centered stimuli with reinforcing or opposing combinations of IIDs and interaural temporal disparities (ITDs). The goal was to assess whether IIDs act as scalars or “weights” within the putative “binaural display” at high spectral frequencies (where the envelopes convey ITD-information) as they have been repeatedly shown to operate at low spectral frequencies (where the waveforms convey ITD-information). They do. The data were accounted for via an augmentation of the cross-correlation-based “position-variable” modeling approach developed by Stern and Shear [J. Acoust. Soc. Am. 100, 2278–2288 (1996)] to account for ITD-based lateralization at low spectral frequencies. In a second context, laterality produced by IIDs (ITD=0) was measured for stimuli centered at either 4 kHz or 500 Hz. The novel finding was that IIDs consistently produced larger extents of laterality at 4 kHz than they did at 500 Hz. [Work supported by research Grant No. NIH DC-04147 from the National Institute on Deafness and Other Communication Disorders, National Institutes of Health.]

Lateralization produced by envelope-based interaural temporal disparities of high-frequency, raised-sine stimuli: Empirical data and modeling

An acoustic pointing task was used to measure extents of laterality produced by ongoing interaural temporal disparities (ITDs) conveyed by the envelopes of 4-kHz-centered raised-sine stimuli while varying, parametrically, their peakedness, depth of modulation, and frequency of modulation. One purpose of the study was to determine whether such manipulations would produce changes in laterality logically consistent with those found for ITD-discrimination thresholds reported by Bernstein and Trahiotis [J. Acoust. Soc. Am. 125, 3234-3242 (2009)]. The data obtained revealed that they did in that (1) increasing depth of modulation, peakedness, or frequency of modulation between 32 and 128 Hz produced smaller threshold ITDs and greater laterality and (2) increasing frequency of modulation to 256 Hz produced modest increases in threshold ITDs and modest decreases in laterality. The extents of laterality measured were successfully accounted for via an augmentation of the cross-correlation-based "position-variable" modeling approach developed by Stern and Shear [J. Acoust. Soc. Am. 100, 2278-2288 (1996)] to account for ITD-based extents of laterality obtained at low spectral frequencies.

Word Processing differences between dyslexic and control children

BackgroundThe aim of this study was to investigate brain responses triggered by different wordclasses in dyslexic and control children. The majority of dyslexic children have difficulties to phonologically assemble a word from sublexical parts following grapheme-to-phoneme correspondences. Therefore, we hypothesised that dyslexic children should mainly differ from controls processing low frequent words that are unfamiliar to the reader.MethodsWe presented different wordclasses (high and low frequent words, pseudowords) in a rapid serial visual word (RSVP) design and performed wavelet analysis on the evoked activity.ResultsDyslexic children had lower evoked power amplitudes and a higher spectral frequency for low frequent words compared to control children. No group differences were found for high frequent words and pseudowords. Control children had higher evoked power amplitudes and a lower spectral frequency for low frequent words compared to high frequent words and pseudowords. This pattern was not present in the dyslexic group.ConclusionDyslexic children differed from control children only in their brain responses to low frequent words while showing no modulated brain activity in response to the three word types. This might support the hypothesis that dyslexic children are selectively impaired reading words that require sublexical processing. However, the lacking differences between word types raise the question if dyslexic children were able to process the words presented in rapid serial fashion in an adequate way. Therefore the present results should only be interpreted as evidence for a specific sublexical processing deficit with caution.

Segmental Rotational Diffusion of Spin-Labeled Polystyrene in Dilute Toluene Solution by 9 and 250 GHz ESR

A copolymer of styrene containing less than 5 mol % of chain units spin-labeled by attachment of the nitroxide via a short tether has been synthesized. ESR spectra of dilute toluene solution of the copolymer have been obtained using 9 and 250 GHz ESR. Parameters characterizing polystyrene segmental rotational diffusion in toluene solution over a broad temperature range have been determined from nonlinear least-squares fits of theoretical ESR spectra to the experimental ESR spectra. The model used was that of relatively fast internal rotation of the nitroxide about its tether, with slower polymer chain segmental motion. Together they lead to effective rotational diffusion with an anisotropic diffusion tensor. In addition, constraints in the form of an orientational potential restrict the range of angles over which this diffusion occurs relative to the polymer backbone, and the latter is assumed to reorient on an ultraslow time scale. This is referred to as a model of microscopic order but macroscopic disorder (MOMD). Rates for the slower polymer chain segmental motion (from the 250 GHz spectra) ranged from 3.6 × 108 s-1 at 311 K to 0.15 × 108 s-1 at 215 K, with a substantial orientational potential of about 2kT over this temperature range. Although there was reasonable agreement between the results obtained at 9 and 250 GHz, there were systematic discrepancies such that the orienting potentials obtained from the 250 GHz spectra were about twice (or more) those from the 9 GHz spectra, and the rotational diffusion tensor components from the 250 GHz spectra were at least twice those from the 9 GHz spectra. This implies a breakdown of the MOMD model for the 9 GHz spectra presumably due to their sensitivity to the slower overall tumbling motion at this low spectral frequency. For the faster “time scale” of the 250 GHz spectra, such a slow motion is “frozen out”, rendering these spectra consistent with the MOMD model. Nevertheless, the results at both frequencies yielded a common activation energy, Eexp = 20.7 ± 1.5 kJ/mol, which, when corrected for the viscous flow contribution, yielded an Ea = 11.9 ± 1.5 kJ/mol, which is in good agreement with recent results from fluorescence studies.

Aproximación al conocimiento del estado del sistema nervioso autónomo en la miocardiopatía hipertrófica mediante el análisis de la variabilidad de la frecuencia cardíaca

The analysis of heart rate variability has been accepted as a non-invasive method to evaluate the influence of the autonomic nervous system over the heart. Although heart rate variability has been used during the last decade in several illnesses the studies in hypertrophic cardiomyopathy are scarce. We report the activity of the autonomic nervous system in patients with hypertrophic cardiomyopathy using the analysis of heart rate variability. Heart rate variability was evaluate by the analyzing 24-h ambulatory electrocardiograms (Holter) in 20 patients with hypertrophic cardiomyopathy and in 15 controls. This method has been used to measure heart rate variability. Spectral analysis of the frequencies were calculated using fast Fourier transformation. Spectral heart rate variability was computed as high (0.15 to 0.40 Hz) low (0.04 to 0.15 Hz) and total (0.01 to 1.0 Hz). We compared the relation between low/high frequency as an index of the sympathetic/parasympathetic balance. All data are expressed as mean value +/- SD. The unpaired Student t-test was used. A two tailed p valued < 0.05 was considered statistically significant. There were no differences in the mean heart rates among the patients with hypertrophic cardiomyopathy and normal subjects (mean +/- SD: 71 +/- 9 versus 74 +/- 11 beats/minute; p = NS) while there was a significant decline in total spectral (mean +/- SD: 7.14 +/- 1.1 versus 7.57 +/- 0.6 ln [ms2]; p = 0.02) and high (mean +/- SD: 5.22 +/- 0.8 versus 5.63 +/- 1.3 ln [ms2]; p = 0.04) as well as in low spectral frequency of heart rate variability (mean +/- SD: 22 +/- 0.8 versus 5.63 +/- 1.3 ln [ms2]; p = 0.04) in patients with hypertrophic cardiomyopathy. There were no differences in the low/high frequency component ratio in these patients (mean +/- SD: 1.1 +/- 0.1 versus 1.2 +/- 0.1 ln [ms2]; p = NS). These facts suggest that the patients with hypertrophic cardiomyopathy have an alteration in the autonomic nervous system: sympathetic (low spectral frequencies) and parasympathetic activity (high spectral frequencies), although this does not reflect an imbalance between sympathetic and parasympathetic activities (relation of low to high spectral frequencies).

Spectral analysis and modelling of ACh and NE effects on shark nervus terminalis activity

We investigated the effects of acetylcholine (ACh) and norepinephrine (NE) on activity in the nervus terminalis (NT) ganglion of the bonnethead shark ( Sphyrna tiburo) using an in vitro preparation and whole nerve recordings. Spectral analysis indicated that ACh (10 and 100 μM) had a variable effect on the total spectral power of whole nerve activity but produced a consistent decrease in half power frequency (HPF; the median frequency of the power spectrum). Norepinephrine (10 μM) reduced baseline activity and total spectral power but produced an increase in HPF in all NT preparations. Computer simulations of extracellular recordings suggested a general explanation for these findings. Acetylcholine may have opposite effects on activity in two NT cell populations with axons in the central nerve trunk, increasing activity in cells whose axons have broad spikes (low spectral frequency) and decreasing activity in cells whose axons have narrow spikes (high spectral frequency). The NE effects are consistent with a decrease in activity of cells whose axons have broad spikes (low spectral frequency) and little or no change in cells whose axons have narrow spikes (high spectral frequency). The physiological data, together with the theoretical analysis, suggest that cholinergic and catecholaminergic neurotransmitter systems are active in the bonnethead NT ganglion, and that ACh and NE have different effects on two populations of ganglion cells.

Electrolocation of Capacitive Objects in Four Species of Pulse‐type Weakly Electric Fish I. Discrimination Performance

AbstractThe great variety of species‐typical electric signals (electric organ discharges, EOD) emitted by weakly electric mormyrid fish might be the result of evolutionary pressures stemming from the two main functions of the electro‐sensory‐motor system: electrocommunication and electrolocation. Employing a conditioned discrimination task we tested four species of mormyrids, emitting EODs differing in waveform, for their ability to detect capacitive properties of objects during electrolocation. Each fish could discriminate capacitive objects within a certain range of capacitive values, which was species specific. The upper and lower limits (upper and lower thresholds) of this detectable range were determined for each fish. In fish species emitting long duration EODs composed of mainly low spectral frequencies both the lower and the upper thresholds were shifted to larger capacitive values compared to fish species emitting shorter EODs. The upper limit of the detectable range was much more variable between species than the lower limit, which was relatively low in all fish. We interpret this as an adaptation of mormyrids to detect small capacitive objects, for example food items. All mormyrids could discriminate between a resistive object and a capacitive object even if the complex impedances of the two objects were identical. This implies that the fish are highly sensitive to small waveform distortions of their self produced EODs.

High-frequency oscillations within early and late phases of the phrenic neurogram.

Spectral analyses were performed on phrenic neurogram recordings from 18 cats to identify high-frequency oscillations (HFOs) inherent in the signals at different phases of inspiratory activity. Gating the analysis for the entire inspiratory phase resulted in dual spectral HFOs (27 and 83 Hz), both of which persisted when the analysis was repeated on the later phase of phrenic inspiratory activity alone (29 and 82 Hz). A third pass at the same data, gating for just the early phase of phrenic discharge, however, resulted in single spectral HFOs at the higher frequency only (86 Hz). Because both early and late recruited phrenic motoneurons carry both higher and lower spectral frequencies, these results demonstrate that the lower frequency HFO is distinctly delayed in onset compared with the higher frequency HFO, the latter of which is believed to have a brain stem origin. This delayed onset may be important in identifying the source of the lower frequency HFO, which appears to be specific to various respiratory efferent systems.

Behavioral responses of weakly electric fish to complex impedances

Members of the family of African electric fish, Mormyridae, exhibit a novelty response, consisting of an acceleration in the rate of electric organ discharges (EODs), when faced with changes in feedback arising from their EODs. In this study, the novelty responses of three different species of mormyrids to shunts with different electrical characteristics were noted. The three species differed in the frequency contents of their EODs: two species had relatively high spectral frequencies in their EODs (>10 kHz), while the third species had only lower spectral frequencies (< 10 kHz). Primarily resistive shunts elicited novelty response accelerations in all three species, and the magnitudes of these responses, when normalized to the responses obtained for a shunt with no introduced resistance, were comparable for all three species. For primarily capacitive shunts, however, the magnitudes of the normalized responses were different for the three species: the two species with high spectral frequencies in their EODs showed larger normalized responses than the third species which had only low EOD spectral frequencies. The differences in species responses for capacitive shunts, and the similarities in species responses for resistive shunts, suggest that electric fish detect the complex impedance of objects in their near field environment: a circuit model consisting of a fish emitting discharges into the surrounding water, which can be shunted by a variable complex impedance, conforms well to the data. Thus, electrolocation is a frequency dependent sensory process, and this frequency dependency should be considered in any speculation about the adaptive value of different EOD waveforms.

The 1/f Fluctuation of a Traffic Current on an Expressway

It is observed that the fluctuation of a traffic current on an expressway obeys the 1/f law for low spectral frequencies. Under proper assumptions the variation of the car concentration is expressed by the Burgers nonlinear differential equation. The observed power spectrum is accounted for as a characteristic feature of the Burgers turbulence.

Spectral basis of auditory "jitter" detection.

The contribution of high-frequency and of low-frequency spectral information to the detection of temporal variability or “jitter” of auditory pulse trains was examined. Pulse trains were subjected to low-pass, to bandpass, and to high-pass filtering. Jitter discrimination for low-frequency pulse trains is substantially poorer than for high-frequency pulse trains. The reason is not that the low spectral frequencies within low-frequency pulse trains interfere with jitter discrimination, nor that low-frequency pulse trains contain insufficient high-frequency spectral information. Rather, it appears that the spacing between high-frequency spectral components of low-frequency pulse trains is too close to permit effective resolution.

Comparison of simultaneous line-of-sight signals at 9.6 and 34.5 GHz

Signals at 9.6 and 34.52 GHz, propagated simultaneously over a slant line-of-sight overwater path, have been analyzed to compare the power spectra of phase-of-arrival variations and fading and to determine the coherence of these signals with regard to both phase variations and fading. The phase data at the two radio frequencies exhibited nearly identical power spectra from 0.01 to 5 Hz and very high coherence from 0.01 to 0.1 Hz. The coherence dropped rapidly above 0.1 Hz and was in most cases less than 0.4 above 0.5 Hz. The power spectra of fading were similar in shape at the two frequencies, but the fading spectral density was consistently higher at 34.52 GHz than at 9.6 GHz from 0.1 to 5 Hz. The shape of the coherence function for fading was similar to that of the corresponding phase coherence function, but the fading coherence was lower at the low spectral frequencies. The possible effect of the small spatial separation of the propagation path on the coherence analysis is discussed.