160 research outputs found
Cyclic and Long-term Variation of Sunspot Magnetic Fields
Measurements from the Mount Wilson Observatory (MWO) are used to study the
long-term variations of sunspot field strengths from 1920 to 1958. Following a
modified approach similar to that in Pevtsov et al. (2011), for each observing
week we select a single sunspot with the strongest field strength measured that
week and then compute monthly averages of these weekly maximum field strengths.
The data show the solar cycle variation of the peak field strengths with an
amplitude of about 500-700 gauss (G), but no statistically significant
long-term trends. Next, we use the sunspot observations from the Royal
Greenwich Observatory (RGO) to establish a relationship between the sunspot
areas and the sunspot field strengths for Cycles 15-19. This relationship is
then used to create a proxy of peak magnetic field strength based on sunspot
areas from the RGO and the USAF/NOAA network for the period from 1874 to early
2012. Over this interval, the magnetic field proxy shows a clear solar cycle
variation with an amplitude of 500-700 G and a weaker long-term trend. From
1874 to around 1920, the mean value of magnetic field proxy increases by about
300-350 G, and, following a broad maximum in 1920-1960, it decreases by about
300 G. Using the proxy for the magnetic field strength as the reference, we
scale the MWO field measurements to the measurements of the magnetic fields in
Pevtsov et al. (2011) to construct a combined data set of maximum sunspot field
strengths extending from 1920 to early 2012. This combined data set shows
strong solar cycle variations and no significant long-term trend (linear fit to
the data yields a slope of 0.8 G year). On the other hand, the
peak sunspot field strengths observed at the minimum of the solar cycle show a
gradual decline over the last three minima (corresponding to cycles 21-23) with
a mean downward trend of 15 G year
Non-LTE Model Atmospheres for Late-Type Stars II. Restricted NLTE Calculations for a Solar-Like Atmosphere
We test our knowledge of the atomic opacity in the solar UV spectrum. Using
the atomic data compiled in Paper I from modern, publicly available, databases,
we perform calculations that are confronted with space-based observations of
the Sun. At wavelengths longer than about 260 nm, LTE modeling can reproduce
quite closely the observed fluxes; uncertainties in the atomic line data
account fully for the differences between calculated and observed fluxes. At
shorter wavelengths, departures from LTE appear to be important, as our LTE and
restricted NLTE calculations differ. Analysis of visible-near infrared Na I and
O I lines, two species that produce a negligible absorption in the UV, shows
that observed departures from LTE for theses species can be reproduced very
accurately with restricted (fixed atmospheric structure) NLTE calculations.Comment: 13 pages, 11 figures, to appear in Ap
Recommended from our members
NBS monograph
From Abstract: "An introductory text gives a detailed description of each column of the solar ledger. Tables include counts of lines of each spectrum recorded in the identification column, leading lines in the first and second spectra, and summaries of molecules and elements present in the sun. About 73 percent of the lines are wholly or partially identified. Sixty-three elements are recorded as present.
Comparison of Training, Anthropometric, Physiological and Psychological Variables of Ultra-Endurance Cyclists and Runners
AbstractWe compared training, anthropometric, physiological and psychological characteristics between 14 cyclists, participants in a 24-hour mountain bike race and 12 runners, participants in a 7-day running ultra-marathon. Methods: Questionnaires and physiological measurements. Results: The differences in ages between cyclists and runners were significant (p << 0.01). The pre-race minus post-race differences (Δ) in body mass (from 76.5 ± 13.1kg to 72.0 ± 12.0kg) and (Δ) in value of hematocrit (6.1 ± 3.5%) were significant only in runners. The post-race minus pre-race difference (Δ) in the rating of perceived exertion was significant in both groups
Evaluating a distortion-weighted glimpsing metric for predicting binaural speech intelligibility in rooms
A distortion-weighted glimpse proportion metric (BiDWGP) for predicting binaural speech intelligibility were evaluated in simulated anechoic and reverberant conditions, with and without a noise masker. The predictive performance of BiDWGP was compared to four reference binaural intelligibility metrics, which were extended from the Speech Intelligibility Index (SII) and the Speech Transmission Index (STI). In the anechoic sound field, BiDWGP demonstrated high accuracy in predicting binaural intelligibility for individual maskers (ρ ≥ 0.95) and across maskers (ρ ≥ 0.94). The reference metrics however performed less well in across-masker prediction (0.54 ≤ ρ ≤ 0.86) despite reasonable accuracy for individual maskers. In reverberant rooms, BiDWGP was more stable in all test conditions (ρ ≥ 0.87) than the reference metrics, which showed different predictive patterns: the binaural STIs were more robust for the stationary than for the fluctuating noise masker, whilst the binaural SII displayed the opposite behaviour. The study shows that the new BiDWGP metric can provide similar or even more robust predictive power than the current standard metric
Does training with amplitude modulated tones affect tone-vocoded speech perception?
Temporal-envelope cues are essential for successful speech perception. We asked here whether training on stimuli containing temporal-envelope cues without speech content can improve the perception of spectrally-degraded (vocoded) speech in which the temporal-envelope (but not the temporal fine structure) is mainly preserved. Two groups of listeners were trained on different amplitude-modulation (AM) based tasks, either AM detection or AM-rate discrimination (21 blocks of 60 trials during two days, 1260 trials; frequency range: 4Hz, 8Hz, and 16Hz), while an additional control group did not undertake any training. Consonant identification in vocoded vowel-consonant-vowel stimuli was tested before and after training on the AM tasks (or at an equivalent time interval for the control group). Following training, only the trained groups showed a significant improvement in the perception of vocoded speech, but the improvement did not significantly differ from that observed for controls. Thus, we do not find convincing evidence that this amount of training with temporal-envelope cues without speech content provide significant benefit for vocoded speech intelligibility. Alternative training regimens using vocoded speech along the linguistic hierarchy should be explored
Summary statistics in auditory perception
Sensory signals are transduced at high resolution, but their structure must be stored in a more compact format. Here we provide evidence that the auditory system summarizes the temporal details of sounds using time-averaged statistics. We measured discrimination of 'sound textures' that were characterized by particular statistical properties, as normally result from the superposition of many acoustic features in auditory scenes. When listeners discriminated examples of different textures, performance improved with excerpt duration. In contrast, when listeners discriminated different examples of the same texture, performance declined with duration, a paradoxical result given that the information available for discrimination grows with duration. These results indicate that once these sounds are of moderate length, the brain's representation is limited to time-averaged statistics, which, for different examples of the same texture, converge to the same values with increasing duration. Such statistical representations produce good categorical discrimination, but limit the ability to discern temporal detail.Howard Hughes Medical Institut
Real-Time Contrast Enhancement to Improve Speech Recognition
An algorithm that operates in real-time to enhance the salient features of speech is described and its efficacy is evaluated. The Contrast Enhancement (CE) algorithm implements dynamic compressive gain and lateral inhibitory sidebands across channels in a modified winner-take-all circuit, which together produce a form of suppression that sharpens the dynamic spectrum. Normal-hearing listeners identified spectrally smeared consonants (VCVs) and vowels (hVds) in quiet and in noise. Consonant and vowel identification, especially in noise, were improved by the processing. The amount of improvement did not depend on the degree of spectral smearing or talker characteristics. For consonants, when results were analyzed according to phonetic feature, the most consistent improvement was for place of articulation. This is encouraging for hearing aid applications because confusions between consonants differing in place are a persistent problem for listeners with sensorineural hearing loss
- …