Submillimeter observations of solar limb-brightening in the total solar eclipse of 31 July 1981

Eight flights of the Kuiper Airborne Observatory (KAO) were devoted to solar observation. The successful observation of a total solar eclipse was accomplished. The observations were made simultaneously at 30, 50, 100, and 200 microns. The successful adaptation of the KAO for solar observations thus provided the most detailed data to date in this spectral band. The results from a preliminary analysis of the KAO data are summarized: (1) the 200 micron limb is extended about 3 arc sec above the 30 micron limb, indicating the prescence of cool dense material up to the altitudes of spicules; (2) strong radial darkening of the quiet sun intensity profile appeared at 200 microns, probably an indication that hot material in the low chromosphere is recessed into vertical magnetic flux tubes embedded in a cooler nonmagnetic substrate, which obscures the heated material approaching the limb; (3) active regions were observed to undergo a strong increase in contrast above the quiet sun background at wave lengths of 100 microns and longer; and (4) the moon was mapped for use as a photometric standard for determining the absolute intensity of the sun in all four wavelength bands

Submillimeter extensions of the solar limb determined from observations of the total eclipse of 1981 July 31

First results are presented of observations of a lunar occultation of the solar limb made from the Kuiper Airborne Observatory in the 30 micrometr, 50 micrometer, 100 micrometer, and 200 micrometer continuum during the total solar eclipse of 1981 July 31. The solar limb was extended at the longer wavelengths up to 1000 km higher than predicted from smooth plane-parallel chromospheric models. Results at both second and third contact show the infrared limb extensions to be approximately 0".8, 1"5, 2".5 and 3".0 above the visible limb in the observed bands, respectively. A possible interpretation proposes chromospheric fine structure inhomogeneities of greater density than presently incorporated in models of the middle chromosphere

How does linguistic knowledge contribute to short-term memory?:Contrasting effects of impaired semantic knowledge and executive control

Background: Linguistic knowledge makes an important contribution to verbal STM. Some theories, including Baddeley's original conception of the episodic buffer, hold that harnessing linguistic knowledge to support STM is executively demanding. However, some recent evidence suggests that the linguistic contribution does not depend on executive resources.Aims: In this study we tested the hypothesis that activation of language representations is automatic and that executive control is most important when the material to be remembered is incompatible with this automatic activation.Methods & Procedures: Word list recall was tested in three patients with transcortical sensory aphasia (TSA) following stroke. All had preserved word repetition and digit span but poor comprehension associated with impaired executive control. They were compared with two semantic dementia (SD) patients with degraded semantic representations but intact executive control. Patients repeated word lists that varied in their semantic and syntactic resemblance to meaningful sentences.Outcomes & Results: The executively impaired TSA patients showed large benefits of semantic and syntactic structure, indicating that their executive deficits did not interfere with the normal linguistic contribution to STM. Instead they showed severe deficits in repetition of scrambled word lists that did not follow usual syntactic rules. On these, the patients changed the word order to better fit their existing knowledge of syntactic structure. In contrast, the SD patients had no problems repeating words in unusual sequences but their semantic knowledge degradation led to frequent phonological errors due to a loss of "semantic binding", the process by which semantic knowledge of words helps to constrain their phonological representation.Conclusions: These findings suggest that linguistic support for STM consists of (a) automatic activation of semantic and syntactic knowledge and (b) executive processes that inhibit this activation when it is incompatible with the material to be remembered. © 2012 Copyright 2012 Psychology Press, an imprint of the Taylor & Francis Group, an Informa business

Extreme limb profiles of the sun at far-infrared and submillimeter wavelengths

Thirty, 50, 100, and 200 microns solar limb intensity profiles determined with arcsecond resolution from airborne observations of the occultation of the solar limb during the total eclipse of 1981 July 31 are presented. Two points of particular importance emerge: (1) the longer-wavelength (100 and 200 micron) limbs are significantly brighter than disk center. At 200 microns the extreme limb is about 1.22 times the brightness of disk center. This is consistent with the 6000 K temperature-plateau structure of the model chromospheres of Vernazza, Avrett, and Loeser (1973, Ap. J., 184, 605; 1981; Ap. J. Suppl., 45, 635;) and (2) the longer wavelength limbs are extended significantly further above the visible limb than Vernazza, Avrett, and Loeser predict. These results provide a strong basis for modeling of the solar chromosphere free from the assumption of gravitational-hydrostatic equilibrium

Superflares on Ordinary Solar-Type Stars

Short duration flares are well known to occur on cool main-sequence stars as well as on many types of `exotic' stars. Ordinary main-sequence stars are usually pictured as being static on time scales of millions or billions of years. Our sun has occasional flares involving up to $\sim 10^{31}$ ergs which produce optical brightenings too small in amplitude to be detected in disk-integrated brightness. However, we identify nine cases of superflares involving $10^{33}$ to $10^{38}$ ergs on normal solar-type stars. That is, these stars are on or near the main-sequence, are of spectral class from F8 to G8, are single (or in very wide binaries), are not rapid rotators, and are not exceedingly young in age. This class of stars includes many those recently discovered to have planets as well as our own Sun, and the consequences for any life on surrounding planets could be profound. For the case of the Sun, historical records suggest that no superflares have occurred in the last two millennia.Comment: 16 pages, accepted for publication in Ap

Varieties of semantic ‘access’ deficit in Wernicke’s aphasia and semantic aphasia

Comprehension deficits are common in stroke aphasia, including in cases with (i) semantic aphasia (SA), characterised by poor executive control of semantic processing across verbal and nonverbal modalities, and (ii) Wernicke’s aphasia (WA), associated with poor auditory-verbal comprehension and repetition, plus fluent speech with jargon. However, the varieties of these comprehension problems, and their underlying causes, are not well-understood. Both patient groups exhibit some type of semantic ‘access’ deficit, as opposed to the ‘storage’ deficits observed in semantic dementia. Nevertheless, existing descriptions suggest these patients might have different varieties of ‘access’ impairment – related to difficulty resolving competition (in SA) vs. initial activation of concepts from sensory inputs (in WA). We used a case-series design to compare WA and SA patients on Warrington’s paradigmatic assessment of semantic ‘access’ deficits. In these verbal and non-verbal matching tasks, a small set of semantically-related items are repeatedly presented over several cycles so that the target on one trial becomes a distractor on another (building up interference and eliciting semantic ‘blocking’ effects). WA and SA patients were distinguished according to lesion location in the temporal cortex, but in each group, some individuals had additional prefrontal damage. Both of these aspects of lesion variability – one that mapped onto classical ‘syndromes’ and one that did not – predicted aspects of the semantic ‘access’ deficit. Both SA and WA cases showed multimodal semantic impairment, although as expected the WA group showed greater deficits on auditory-verbal than picture judgements. Distribution of damage in the temporal lobe was crucial for predicting the initially beneficial effects of stimulus repetition: WA cases showed initial improvement with repetition of words and pictures, while in SA, semantic access was initially good but declined in the face of competition from previous targets. Prefrontal damage predicted the harmful effects of repetition: the ability to re-select both word and picture targets in the face of mounting competition was linked to left prefrontal damage in both groups. Therefore, SA and WA patients have partially distinct impairment of semantic ‘access’ but, across these syndromes, prefrontal lesions produce declining comprehension with repetition in both verbal and non-verbal tasks

Numerical simulations of conversion to Alfven waves in sunspots

We study the conversion of fast magneto-acoustic waves to Alfven waves by means of 2.5D numerical simulations in a sunspot-like magnetic configuration. A fast, essentially acoustic, wave of a given frequency and wave number is generated below the surface and propagates upward though the Alfven/acoustic equipartition layer where it splits into upgoing slow (acoustic) and fast (magnetic) waves. The fast wave quickly reflects off the steep Alfven speed gradient, but around and above this reflection height it partially converts to Alfven waves, depending on the local relative inclinations of the background magnetic field and the wavevector. To measure the efficiency of this conversion to Alfven waves we calculate acoustic and magnetic energy fluxes. The particular amplitude and phase relations between the magnetic field and velocity oscillations help us to demonstrate that the waves produced are indeed Alfven waves. We find that the conversion to Alfven waves is particularly important for strongly inclined fields like those existing in sunspot penumbrae. Equally important is the magnetic field orientation with respect to the vertical plane of wave propagation, which we refer to as "field azimuth". For field azimuth less than 90 degrees the generated Alfven waves continue upwards, but above 90 degrees downgoing Alfven waves are preferentially produced. This yields negative Alfven energy flux for azimuths between 90 and 180 degrees. Alfven energy fluxes may be comparable to or exceed acoustic fluxes, depending upon geometry, though computational exigencies limit their magnitude in our simulations.Comment: Accepted for publication in Ap

Semantic diversity:A measure of contextual variation in word meaning based on latent semantic analysis

Semantic ambiguity is typically measured by summing the number of senses or dictionary definitions that a word has. Such measures are somewhat subjective and may not adequately capture the full extent of variation in word meaning, particularly for polysemous words that can be used in many different ways, with subtle shifts in meaning. Here, we describe an alternative, computationally derived measure of ambiguity based on the proposal that the meanings of words vary continuously as a function of their contexts. On this view, words that appear in a wide range of contexts on diverse topics are more variable in meaning than those that appear in a restricted set of similar contexts. To quantify this variation, we performed latent semantic analysis on a large text corpus to estimate the semantic similarities of different linguistic contexts. From these estimates, we calculated the degree to which the different contexts associated with a given word vary in their meanings. We term this quantity a word's semantic diversity (SemD). We suggest that this approach provides an objective way of quantifying the subtle, context-dependent variations in word meaning that are often present in language. We demonstrate that SemD is correlated with other measures of ambiguity and contextual variability, as well as with frequency and imageability. We also show that SemD is a strong predictor of performance in semantic judgments in healthy individuals and in patients with semantic deficits, accounting for unique variance beyond that of other predictors. SemD values for over 30,000 English words are provided as supplementary materials. © 2012 Psychonomic Society, Inc

Echinoderms have bilateral tendencies

Echinoderms take many forms of symmetry. Pentameral symmetry is the major form and the other forms are derived from it. However, the ancestors of echinoderms, which originated from Cambrian period, were believed to be bilaterians. Echinoderm larvae are bilateral during their early development. During embryonic development of starfish and sea urchins, the position and the developmental sequence of each arm are fixed, implying an auxological anterior/posterior axis. Starfish also possess the Hox gene cluster, which controls symmetrical development. Overall, echinoderms are thought to have a bilateral developmental mechanism and process. In this article, we focused on adult starfish behaviors to corroborate its bilateral tendency. We weighed their central disk and each arm to measure the position of the center of gravity. We then studied their turning-over behavior, crawling behavior and fleeing behavior statistically to obtain the center of frequency of each behavior. By joining the center of gravity and each center of frequency, we obtained three behavioral symmetric planes. These behavioral bilateral tendencies might be related to the A/P axis during the embryonic development of the starfish. It is very likely that the adult starfish is, to some extent, bilaterian because it displays some bilateral propensity and has a definite behavioral symmetric plane. The remainder of bilateral symmetry may have benefited echinoderms during their evolution from the Cambrian period to the present