Changes In Spectral Slope Research Articles

Brightening and Fading in the Youngest Galactic Supernova Remnant G1.9+0.3: 13 Years of Monitoring with the Chandra X-Ray Observatory

We report 13 years of Chandra monitoring of the youngest Galactic supernova remnant G1.9+0.3, the only remnant known to be increasing in brightness. We confirm the spatially integrated rate of flux increase of (1.2 ± 0.2)% yr−1 (1–7 keV), but find large spatial variations, from −3% yr−1 to +7% yr−1, over length scales as small as 10″ or smaller. We observe relatively little change in spectral slope, though one region shows significant hardening as it brightens by 1% yr−1. Such rates of change can be accommodated by any of several explanations, including steady blast-wave evolution, expansion or compression of discrete plasma blobs, magnetic turbulence, or variations in magnetic-field aspect angle. Our results do not constrain the mean magnetic-field strength, but a self-consistent picture can be produced in which the maximum particle energies are limited by the remnant age (applying both to electrons and to ions) to about 20 TeV, and the remnant-averaged magnetic-field strength is about 30 μG. The deceleration parameter m (average shock radius varying as t m ) is about 0.7, consistent with estimates from overall expansion dynamics and confirming an explosion date of about 1900 CE. Shock-efficiency factors ϵ e and ϵ B (fractions of shock energy in relativistic electrons and magnetic field) are 0.003 and 0.0002 in this picture. However, the large range of rates of brightness change indicates that such a global model is oversimplified. Temporal variations of photon index, expected to be small but measurable with longer time baselines, can discriminate among possible models.

Space weathering, grain size, and metamorphic heating effects on ordinary chondrite spectral reflectance parameters

AbstractThe exposure to irradiation from high‐energy particles alters the reflectance properties of asteroid surfaces and is referred to as space weathering. This process leads to an increase in spectral slope in visible and near‐infrared wavelengths. However, changes in the regolith particle size, which can vary dramatically among the asteroid population, are known to influence the spectral properties of meteorites and asteroids. In this context, we investigate the changes in spectral slope and absorption band depths of fresh and irradiated ordinary chondrite meteorites to quantitatively compare the effects of space weathering and grain size variations. To do so, we develop and employ the Spectral Analysis for Asteroid Reflectance Investigation routine that calculates the band parameters of reflectance spectra. We then formulate a parameter called the Space Weathering Index (SWI) that is designed to encapsulate spectral changes due to space weathering. We find that the SWI is strongly dependent on the spectral slope which complicates the interpretation of asteroid spectra in the context of grain size variations and space weathering. We also show that a second parameter, the Band Depth Index, is indicative of petrologic type. Finally, we use a linear discriminant analysis to classify asteroid reflectance spectra into H, L, LL, and unequilibrated ordinary chondrites.

Multifactor characterization of space weathering among siliceous asteroids. I: Grain size effects

AbstractSpacecraft missions to asteroids have revealed surfaces that have variations in albedo and spectral properties. Such variations are also detected across the asteroid population with ground‐based observations, and are controlled by the physical characteristics of the regolith and by processes such as space weathering. Here, we investigate how space weathering and regolith grain size influence the spectra of ordinary chondrite‐like asteroids observed from ground‐based spectroscopy. The estimation of diagnostic band parameters from asteroid visible and near‐infrared reflectance spectra allow us to estimate the degree of space weathering and their compositions, using results from an accompanying study (MacLennan et al., 2024). We use grain size estimations gleaned from the thermal inertia to show that regolith particle size differences have similar effect as space weathering on asteroid spectra. Finally, we quantify changes in spectral slope and band depth among asteroids using the space weathering index developed by MacLennan et al (2024), and reassess the importance of previously‐proposed surface freshening mechanisms.

In Vivo Photoacoustic Monitoring of Stem Cell Location and Apoptosis with Caspase-3-Responsive Nanosensors.

Stem cell therapy has immense potential in a variety of regenerative medicine applications. However, clinical stem cell therapy is severely limited by challenges in assessing the location and functional status of implanted cells in vivo. Thus, there is a great need for longitudinal, noninvasive stem cell monitoring. Here we introduce a multidisciplinary approach combining nanosensor-augmented stem cell labeling with ultrasound guided photoacoustic (US/PA) imaging for the spatial tracking and functional assessment of transplanted stem cell fate. Specifically, our nanosensor incorporates a peptide sequence that is selectively cleaved by caspase-3, the primary effector enzyme in mammalian cell apoptosis; this cleavage event causes labeled cells to show enhanced optical absorption in the first near-infrared (NIR) window. Optimization of labeling protocols and spectral characterization of the nanosensor in vitro showed a 2.4-fold increase in PA signal from labeled cells during apoptosis while simultaneously permitting cell localization. We then successfully tracked the location and apoptotic status of mesenchymal stem cells in a mouse hindlimb ischemia model for 2 weeks in vivo, demonstrating a 4.8-fold increase in PA signal and spectral slope changes in the first NIR window under proapoptotic (ischemic) conditions. We conclude that our nanosensor allows longitudinal, noninvasive, and nonionizing monitoring of stem cell location and apoptosis, which is a significant improvement over current end-point monitoring methods such as biopsies and histological staining of excised tissue.

0194 Sources of variation in the spectral slope of the sleep EEG

Abstract Introduction The 1/f spectral slope of the electroencephalogram (EEG) estimated in the gamma frequency range has been shown to reflect neural excitation/inhibition ratio and synchronization level within local neural populations. It was proposed as an arousal marker that differentiates wake, non-rapid eye movement (NREM) sleep, and rapid eye movement (REM) sleep. These stages exhibit progressively steeper 30-45 Hz slopes, interpreted in terms of increasing cortical inhibition. Here we sought to replicate these findings in a larger sample and provide a comprehensive characterization of how slope changes with age, sex, and its test-retest reliability as well as potential confounds that could affect the slope estimation. Methods After stringent exclusions and quality control, our final sample included 10,255 whole-night polysomnograms (PSGs) on 7,312 individuals 2,943 of whom had a second PSG, from the National Sleep Research Resource (NSRR). All preprocessing steps were performed using an open-source Luna package and the spectral slope was estimated by fitting log-log linear regression models on the absolute power from 30 to 45 Hz separately for wake, NREM and REM stages. We described sources of variation in the spectral slope (both within and between individuals) and its relationship to other sleep parameters including power and interhemispheric coherence. Results There was unambiguous statistical support for the hypothesis that, within individuals, the mean spectral slope grows steeper going from wake to NREM to REM sleep. We found that the choice of mastoid referencing scheme modulated the extent to which electromyogenic or electrocardiographic artifacts were likely to bias 30-45 Hz slope estimates, as well as other sources of technical, device-specific bias. Nonetheless, within individuals, slope estimates were relatively stable over time. Both cross-sectionally and longitudinal, slopes tended to become shallower with increasing age, particularly for REM sleep; males tended to show flatter slopes than females across all states. Although conceptually distinct, spectral slope did not predict sleep state substantially better than other summaries of the high-frequency EEG power spectrum (>20 Hz, in this context) including beta band power, however. In contrast to the common conception of the REM EEG as relatively wake-like (i.e. ‘paradoxical’ sleep), REM and wake were the most divergent states for multiple metrics, with NREM exhibiting intermediate profiles. Under a simplified modeling framework, changes in spectral slope could not, by themselves, fully account for the observed differences between states, if assuming a strict power-law model. Conclusion Although the spectral slope is appealing, theoretically inspired parameterization of the sleep EEG, we underscore some practical considerations that should be borne in mind when applying it in diverse datasets. Future work will be needed to fully characterize state-dependent changes in the aperiodic portions of the EEG power spectra, which appear to be consistent with, albeit not fully explained by, changes in the spectral slope. Support (If Any)

SORCE and TSIS‐1 SIM Comparison: Absolute Irradiance Scale Reconciliation

AbstractThe Solar Radiation and Climate Experiment (SORCE) and Total and Spectral Irradiance Sensor (TSIS‐1) conducted an intercomparison for the two Spectral Irradiance Monitors (SIM) spanning 704 days from 23 March 2018 to 25 February 2020 and permitted 554 time‐matched pairs of observations. This comparison was conducted during the extremely quiescent Solar Cycle 24 minimum, so all observed differences and drifts between the two sensors are instrumental in nature. The TSIS‐1 SIM benefitted from advanced calibration capabilities based on SI standards that were not available during the preflight calibration time period of SORCE. For this reason, a revision of the SORCE SIM absolute scale is appropriate. As expected, wavelength dependent differences in absolute agreement are a function of detector sensitivity and local changes in spectral slope. At the time of the comparison SORCE SIM has been on‐orbit for 17 years while TSIS‐1 observations commenced immediately after a 100‐day outgassing and commissioning period. Peak‐to‐peak absolute scale differences are about 12% with a mean fractional difference of 0.7% ± 2.9%. The greatest scale differences occur at the change‐over between the UV and visible photodiodes in the 310 nm region, and a systematic disagreement is present in the 850–1,600 nm range. A multiplicative scale correction factor has been developed to reconcile the TSIS‐1 and SORCE difference with a wavelength dependent error on the mean typically less than 0.01% derived from every matched pair of observations.

Comparison of space weathering spectral changes induced by solar wind and micrometeoroid impacts using ion- and femtosecond-laser-irradiated olivine and pyroxene

Context.Space weathering is a process that changes the surface of airless planetary bodies. Prime space weathering agents are solar wind irradiation and micrometeoroid bombardment. These processes alter planetary reflectance spectra and often modify their compositional diagnostic features.Aims.In this work we focused on simulating and comparing the spectral changes caused by solar wind irradiation and by micrometeoroid bombardment to gain a better understanding of these individual space weathering processes.Methods.We used olivine and pyroxene pellets as proxies for planetary materials. To simulate solar wind irradiation we used hydrogen, helium, and argon ions with energies from 5 to 40 keV and fluences of up to 1018particles cm−2. To simulate micrometeoroid bombardment we used individual femtosecond laser pulses. We analysed the corresponding evolution of different spectral parameters, which we determined by applying the Modified Gaussian Model, and we also conducted principal component analysis.Results.The original mineralogy of the surface influences the spectral evolution more than the weathering agent, as seen from the diverse evolution of the spectral slope of olivine and pyroxene upon irradiation. The spectral slope changes seen in olivine are consistent with observations of A-type asteroids, while the moderate to no slope changes observed in pyroxene are consistent with asteroid (4) Vesta. We also observed some differences in the spectral effects induced by the two weathering agents. Ions simulating solar wind have a smaller influence on longer wavelengths of the spectra than laser irradiation simulating micrometeoroid impacts. This is most likely due to the different penetration depths of ions and laser pulses. Our results suggest that in some instances it might be possible to distinguish between the contributions of the two agents on a weathered surface.

Space Weathering within C-complex Main Belt Asteroid Families

Abstract Using data from the Sloan Digital Sky Survey Moving Object Catalog, we study color as a function of size for C-complex families in the main asteroid belt to improve our understanding of space weathering of carbonaceous materials. We find two distinct spectral slope trends: Hygiea type and Themis type. The Hygiea-type families exhibit a reduction in spectral slope with increasing object size until a minimum slope value is reached and the trend reverses with increasing slope with increasing object size. The Themis family shows an increase in spectral slope with increasing object size until a maximum slope is reached and the spectral slope begins to decrease slightly or plateaus for the largest objects. Most families studied show the Hygiea-type trend. The processes responsible for these distinct changes in spectral slope affect several different taxonomic classes within the C-complex and appear to act quickly to alter the spectral slopes of the family members.

Distinguishing between Shock-darkening and Space-weathering Trends in Ordinary Chondrite Reflectance Spectra

Abstract Space-weathering as well as shock effects can darken meteorite and asteroid reflectance spectra. We present a detailed comparative study on shock-darkening and space-weathering using different lithologies of the Chelyabinsk LL5 chondrite. Compared to space-weathering, the shock processes do not cause significant spectral slope changes and are more efficient in attenuating the orthopyroxene 2 μm absorption band. This results in a distinct shock vector in the reflectance spectra principal component analysis, moving the shocked silicate-rich Chelyabinsk spectra from the S-complex space into the C/X complex. In contrast to this, the space-weathering vector stays within the S complex, moving from Q type to S type. Moreover, the 2 μm to 1 μm band depth ratio (BDR) as well as the 2 μm to 1 μm band area ratio (BAR) are not appreciably affected by shock-darkening or shock melting. Space-weathering, however, causes significant shifts in both BDR and BAR toward higher values. Application of the BDR method to the three distinct areas on the asteroid Itokawa reveals that Itokawa is rather uniformly space-weathered and not influenced by regolith roughness or relative albedo changes.

Control of vocal loudness in singing

Vocal loudness in sones is quantified on the basis of changes in spectral slope and harmonic tuning in a range of singing fundamental frequencies of 125 Hz to 1000 Hz. Spectral slope of the mouth output pressure is bracketed in the range of -3 dB/octave to -12 dB/octave to reflect a typical glottal spectrum from breathy to pressed adduction. To approximate formant tuning of harmonics, the SPL level of the first three harmonics is raised by 10, 20, and 30 dB. It is shown that spectral slope change is more effective in increasing vocal loudness than tuning a single harmonic with a vocal tract resonance. Some applications to amplified and unamplified vocal production and respective training are given.

Variability and Proper Motion of X-Ray Knots in the Jet of Centaurus A

Abstract We report results from Chandra observations analyzed for evidence of variability and proper motion in the X-ray jet of Centaurus A. Using data spanning 15 yr, collective proper motion of 11.3 ± 3.3 mas yr−1, or 0.68 ± 0.20c, is detected for the fainter X-ray knots and other substructure present within the jet. The three brightest knots (AX1A, AX1C, and BX2) are found to be stationary to an upper limit of . Brightness variations up to 27% are detected for several X-ray knots in the jet. For the fading knots, BX2 and AX1C, the changes in spectral slope expected to accompany synchrotron cooling are not found, ruling it out and placing upper limits of ≃80 μG for each of their magnetic field strengths. Adiabatic expansion can account for the observed decreases in brightness. Constraints on models for the origin of the knots are established. Jet plasma overrunning an obstacle is favored as the generator of stationary knots, while moving knots are likely produced either by internal differences in jet speed or the late stages of jet interaction with nebular or cloud material.

Spectral reflectance “deconstruction” of the Murchison CM2 carbonaceous chondrite and implications for spectroscopic investigations of dark asteroids

Carbonaceous chondrites (CCs) are important materials for understanding the early evolution of the solar system and delivery of volatiles and organic material to the early Earth. Presumed CC-like asteroids are also the targets of two current sample return missions: OSIRIS-REx to asteroid Bennu and Hayabusa-2 to asteroid Ryugu, and the Dawn orbital mission at asteroid Ceres. To improve our ability to identify and characterize CM2 CC-type parent bodies, we have examined how factors such as particle size, particle packing, and viewing geometry affect reflectance spectra of the Murchison CM2 CC. The derived relationships have implications for disc-resolved examinations of dark asteroids and sampleability. It has been found that reflectance spectra of slabs are more blue-sloped (reflectance decreasing toward longer wavelengths as measured by the 1.8/0.6 µm reflectance ratio), and generally darker, than powdered sample spectra. Decreasing the maximum grain size of a powdered sample results in progressively brighter and more red-sloped spectra. Decreasing the average grain size of a powdered sample results in a decrease in diagnostic absorption band depths, and redder and brighter spectra. Decreasing porosity of powders and variations in surface texture result in spectral changes that may be different as a function of viewing geometry. Increasing thickness of loose dust on a denser powdered substrate leads to a decrease in absorption band depths. Changes in viewing geometry lead to different changes in spectral metrics depending on whether the spectra are acquired in backscatter or forward-scatter geometries. In backscattered geometry, increasing phase angle leads to an initial increase and then decrease in spectral slope, and a general decrease in visible region reflectance and absorption band depths, and frequent decreases in absorption band minima positions. In forward scattering geometry, increasing phase angle leads to small non-systematic changes in spectral slope, and general decreases in visible region reflectance, and absorption band depths. The highest albedos and larger band depths are generally seen in the lowest phase angle backscattering geometry spectra. The reddest spectra are generally seen in the lowest phase angle backscatter geometry spectra. For the same phase angle, spectra acquired in forward scatter geometry are generally redder and darker and have shallower absorption bands than those acquired in backscatter geometry. Overall, backscatter geometry-acquired spectra are flatter, brighter, and have deeper 0.7 µm region absorption band depths than forward scatter geometry-acquired spectra. It was also found that the 0.7, 0.9, and 1.1 µm absorption bands in Murchison spectra, which are attributable to various Fe electronic processes, are ubiquitous and can be used to recognize CM2 chondrites regardless of the physical properties of the meteorite and viewing geometry.

Space weathering trends on carbonaceous asteroids: A possible explanation for Bennu’s blue slope?

We compare primitive near-Earth asteroid spectral properties to the irradiated carbonaceous chondrite samples of Lantz et al. (2017) in order to assess how space weathering processes might influence taxonomic classification.Using the same eigenvectors from the asteroid taxonomy by DeMeo et al. (2009), we calculate the principal components for fresh and irradiated meteorites and find that change in spectral slope (blueing or reddening) causes a corresponding shift in the two first principal components along the same line that the C- and X-complexes track. Using a sample of B-, C-, X-, and D-type NEOs with visible and near-infrared spectral data, we further investigated the correlation between prinicipal components and the spectral curvature for the primitive asteroids. We find that space weathering effects are not just slope and albedo, but also include spectral curvature.We show how, through space weathering, surfaces having an original “C-type” reflectance can thus turn into a redder P-type or a bluer B-type, and that space weathering can also decrease (and disguise) the D-type population.Finally we take a look at the case of OSIRIS-REx target (101955) Bennu and propose an explanation for the blue and possibly red spectra that were previously observed on different locations of its surface: parts of Bennu’s surface could have become blue due to space weathering, while fresher areas are redder. No clear prediction can be made on Hayabusa-2 target (162173) Ryugu.

High-frequency ultrasound detection of cell death: Spectral differentiation of different forms of cell death in vitro.

High frequency quantitative ultrasound techniques were investigated to characterize different forms of cell death in vitro. Suspension-grown acute myeloid leukemia cells were treated to cause apoptosis, oncosis, mitotic arrest, and heat-induced death. Samples were scanned with 20 and 40 MHz ultrasound and assessed histologically in terms of cellular structure. Frequency-domain analysis of 20 MHz ultrasound data demonstrated midband fit changes of 6.0 ± 0.7 dBr, 6.2 ± 1.8 dBr, 4.0 ± 1.0 dBr and −4.6 ± 1.7 dBr after 48-hour cisplatinum-induced apoptosis, 48-hour oncotic decay, 36-hour colchicine-induced mitotic arrest, and heat treatment compared to control, respectively. Trends from 40 MHz ultrasound were similar. Spectral slope changes obtained from 40 MHz ultrasound data were reflective of alterations in cell and nucleus size. Chromatin pyknosis or lysis trends suggested that the density of nuclear material may be responsible for observed changes in ultrasound backscatter. Flow cytometry analysis confirmed the modes of cell death and supported midband fit trends in ultrasound data. Scatterer-size and concentration estimates obtained from a fluid-filled sphere form factor model further corresponded with spectral analysis and histology. Results indicate quantitative ultrasound spectral analysis may be used for probing anti-cancer response and distinguishing various modes of cell death in vitro.

Modeling the voice source in terms of spectral slopes

A psychoacoustic model of the voice source spectrum is proposed. The model is characterized by four spectral slope parameters: the difference in amplitude between the first two harmonics (H1-H2), the second and fourth harmonics (H2-H4), the fourth harmonic and the harmonic nearest 2 kHz in frequency (H4-2 kHz), and the harmonic nearest 2 kHz and that nearest 5 kHz (2 kHz-5 kHz). As a step toward model validation, experiments were conducted to establish the acoustic and perceptual independence of these parameters. In experiment 1, the model was fit to a large number of voice sources. Results showed that parameters are predictable from one another, but that these relationships are due to overall spectral roll-off. Two additional experiments addressed the perceptual independence of the source parameters. Listener sensitivity to H1-H2, H2-H4, and H4-2 kHz did not change as a function of the slope of an adjacent component, suggesting that sensitivity to these components is robust. Listener sensitivity to changes in spectral slope from 2 kHz to 5 kHz depended on complex interactions between spectral slope, spectral noise levels, and H4-2 kHz. It is concluded that the four parameters represent non-redundant acoustic and perceptual aspects of voice quality.

Ensemble spectral variability study of Active Galactic Nuclei from the XMM-Newton serendipitous source catalogue

The variability of the X-Ray spectra of active galactic nuclei (AGN) usually includes a change of the spectral slope. This has been investigated for a small sample of local AGNs by Sobolewska and Papadakis [1], who found that slope variations are well correlated with flux variations, and that the spectra are typically steeper in the bright phase (softer when brighter behaviour). Not much information is available for the spectral variability of high-luminosity AGNs and quasars. In order to investigate this phenomenon, we use data from the XMM-Newton Serendipitous Source Catalogue, Data Release 5, which contains X- Ray observations for a large number of active galactic nuclei in a wide luminosity and redshift range, for several different epochs. This allows to perform an ensemble analysis of the spectral variability for a large sample of quasars. We quantify the spectral variability through the spectral variability parameter β, defined by Trevese and Vagnetti [2] as the ratio between the change in spectral slope and the corresponding logarithmic flux variation. We find that the spectral variability of quasars has a softer when brighter behaviour, similarly to local AGNs.

Orbital multispectral mapping of Mercury with the MESSENGER Mercury Dual Imaging System: Evidence for the origins of plains units and low-reflectance material

A principal data product from MESSENGER’s primary orbital mission at Mercury is a global multispectral map in eight visible to near-infrared colors, at an average pixel scale of 1km, acquired by the Mercury Dual Imaging System. The constituent images have been calibrated, photometrically corrected to a standard geometry, and map projected. Global analysis reveals no spectral units not seen during MESSENGER’s Mercury flybys and supports previous conclusions that most spectral variation is related to changes in spectral slope and reflectance between spectral end-member high-reflectance red plains (HRP) and low-reflectance material (LRM). Comparison of color properties of plains units mapped on the basis of morphology shows that the two largest unambiguously volcanic smooth plains deposits (the interior plains of Caloris and the northern plains) are close to HRP end members and have average color properties distinct from those of most other smooth plains and intercrater plains. In contrast, smaller deposits of smooth plains are nearly indistinguishable from intercrater plains on the basis of their range of color properties, consistent with the interpretation that intercrater plains are older equivalents of smooth plains. LRM having nearly the same reflectance is exposed in crater and basin ejecta of all ages, suggesting impact excavation from depth of material that is intrinsically dark or darkens very rapidly, rather than gradual darkening of exposed material purely by space weathering. A global search reveals no definitive absorptions attributable to Fe2+-containing silicates or to sulfides over regions 20km or more in horizontal extent, consistent with results from MESSENGER’s Mercury Atmospheric and Surface Composition Spectrometer. The only absorption-like feature identified is broad upward curvature of the spectrum centered near 600nm wavelength. The feature is strongest in freshly exposed LRM and weak or absent in older exposures of LRM. We modeled spectra of LRM as intimate mixtures of HRP with candidate low-reflectance phases having a similar 600-nm spectral feature, under the assumption that the grain size is 1μm or larger. Sulfides measured to date in the laboratory and coarse-grained iron are both too bright to produce LRM from HRP. Ilmenite is sufficiently dark but would require Ti abundances too high to be consistent with MESSENGER X-Ray Spectrometer measurements. Three phases or mixtures of phases that could be responsible for the low reflectance of LRM are consistent with our analyses. Graphite, in amounts consistent with upper limits from the Gamma-Ray Spectrometer, may be consistent with geochemical models of Mercury’s differentiation calling for a graphite-enriched primary flotation crust from an early magma ocean and impact mixing of that early crust before or during the late heavy bombardment (LHB) into material underlying the volcanic plains. The grain size of preexisting iron or iron sulfide could have been altered to a mix of nanophase and microphase grains by shock during those impacts, lowering reflectance. Alternatively, iron-bearing phases and carbon in a late-accreting carbonaceous veneer may have been stirred into the lower crust or upper mantle. Decoupling of variations in color from abundances of major elements probably results from the very low content and variation of Fe2+ in crustal silicates, such that reflectance is controlled instead by one or more minor opaque phases and the extent of space weathering.

The organic-rich surface of comet 67P/Churyumov-Gerasimenko as seen by VIRTIS/Rosetta

The VIRTIS (Visible, Infrared and Thermal Imaging Spectrometer) instrument on board the Rosetta spacecraft has provided evidence of carbon-bearing compounds on the nucleus of the comet 67P/Churyumov-Gerasimenko. The very low reflectance of the nucleus (normal albedo of 0.060 ± 0.003 at 0.55 micrometers), the spectral slopes in visible and infrared ranges (5 to 25 and 1.5 to 5% kÅ(-1)), and the broad absorption feature in the 2.9-to-3.6-micrometer range present across the entire illuminated surface are compatible with opaque minerals associated with nonvolatile organic macromolecular materials: a complex mixture of various types of carbon-hydrogen and/or oxygen-hydrogen chemical groups, with little contribution of nitrogen-hydrogen groups. In active areas, the changes in spectral slope and absorption feature width may suggest small amounts of water-ice. However, no ice-rich patches are observed, indicating a generally dehydrated nature for the surface currently illuminated by the Sun.

Olivine–metal mixtures: Spectral reflectance properties and application to asteroid reflectance spectra

Olivine-rich asteroids appear to be common in the main asteroid belt as well as present in the near-Earth asteroid population. There are a number of meteorite classes that are dominated by olivine±metal. To determine whether relationships exist between these asteroids and meteorites, we spectrally characterized a number of olivine+meteoritic metal powder intimate and areal mixtures, pallasite slabs, and olivine powders on a metal slab. Our goal is to understand the spectral characteristics of olivine+metal assemblages and develop spectral metrics that can be used to analyze reflectance spectra of olivine-dominated asteroids. We found that the major olivine absorption band in the 1μm region is resolvable in intimate mixtures for metal abundances as high as ∼90wt.%. The wavelength position of the 1μm region olivine absorption band center is sensitive to Fa content but insensitive to other variables. However, the band minimum position moves to shorter wavelengths with increasing metal abundance due to changes in spectral slope. The full width at half maximum (FWHM) of this band and reflectance at 1.8μm are both most sensitive to olivine Fa content, metal abundance, and grain size, and much less to the presence of nanophase iron that reddens spectra. Reflectance at 0.56μm and the 1.8/0.56μm reflectance ratio are sensitive to these same parameters as well as to nanophase iron-associated spectral reddening. The wavelength position of the local reflectance maximum in the 0.7μm region moves to longer wavelengths with increasing metal abundance and is most useful for constraining metal abundance in high metal-content mixtures. Pallasite slab spectra differ in a number of respects from powdered assemblages and multiple spectral parameters can be used to discriminate them. The spectra of increasingly fine-grained olivine+metal assemblages and those involving low-Fa olivine show increasing spectral dominance by metal. Systematic application of multiple spectral metrics allows olivine+metal assemblage properties such as Fa content, olivine/metal ratio, and grain size to be quantified or constrained. Analysis of reflectance spectra of 22 presumed olivine±metal-rich asteroids indicates that most of them possess low- to medium-Fa content olivine (Fa<∼67), with variable abundances of macroscopic metal. A number exhibit visible region absorption bands that are indicative of some fraction of coarser-grained olivine (>45μm). Most asteroid spectra can be plausibly linked to specific olivine±metal-bearing meteorite classes. Most of the asteroid spectra examined exhibit some degree of spectral reddening below ∼1.8μm which is most consistent with the presence of fine-grained nanophase iron, likely produced by space weathering.

The Effect of Change in Spectral Slope and Formant Frequencies on the Perception of Loudness

This study attempts to understand how changes in spectral slope and formant frequency influence changes in perceived loudness. It was hypothesized that voices synthesized with steeper spectral slopes will be perceived as less loud than voices synthesized with less steep spectral slopes, in spite of the fact that they are of equal root mean square (RMS) amplitude. It was also hypothesized that stimuli with higher formant patterns will be perceived as louder than those with lower formant patterns, in spite of the fact that they are of equal RMS amplitude. Repeated measures factorial design. For the pitches A3, C4, B4, and F5, three different source signals were synthesized with varying slopes of -9, -12, and -15 dB/octave using a frequency vibrato rate of 5.6 Hz and a frequency vibrato extent of 50 cents. Each of the three source signals were filtered using two formant patterns, a lower formant pattern typical of a mezzo-soprano (pattern A) and a higher formant pattern typical of a soprano (pattern B) for the vowel /a/. For each pitch, the six stimuli were combined into all possible pairs and normalized to equal RMS amplitude. Listeners were presented with 120 paired stimuli (60 pairs repeated twice). The listener's task was to indicate whether the first or second stimulus in the pair was louder. Generally, as the spectral slope decreased, perceived loudness increased, with the magnitude of the perceived difference in loudness being related to the degree of difference in spectral slope. Likewise, at all pitches except A3, perceived loudness increased as formant frequency increased. RMS amplitude is an important predictor of loudness perception, but many other factors also affect the perception of this important vocal parameter. Spectral composition is one such factor and must be considered when using loudness perception in the process of clinical diagnostics.