4,221 research outputs found
Cognitive and psychosocial deficits in agenesis of the corpus callosum with normal intelligence
Cognitive disabilities in agenesis of the corpus callosum (ACC) have been described in scattered reports, but few complete case descriptions are available. Consequent psychosocial disabilities in ACC have received little attention. We expected that ACC would be manifest in deficits specific to complex reasoning, concept formation, and problem solving. We also expected that these cognitive problems would be particularly evident in difficulties interpreting and understanding social situations, and in abnormal self-perception. Methods. Cognitive and psychosocial deficits were studied in two adolescents with ACC and normal IQ using a battery of cognitive and psychological tests. Results. Test results indicated poor interhemispheric integration of complex material. Performance on tests of reasoning, and concept formation were clearly below expectations based on IQ. Significantly poor performance was also found on tests of social insight, proverb interpretation, social logic, self-perception, and interpretation of ambiguous stimuli. Gross behavioural disorder or psychopathology were not found. Conclusions. ACC results in disabilities in social cognition that appear to be secondary to deficits in complex cognitive operations such as reasoning, concept formation, and problem solving. It is suggested that these cognitive deficits may be related to diminished interhemispheric transfer of complex information
A New Gravitational Wave Verification Source
We report the discovery of a detached 20 min orbital period binary white
dwarf. WD0931+444 (SDSS J093506.93+441106.9) was previously classified as a WD
+ M dwarf system based on its optical spectrum. Our time-resolved optical
spectroscopy observations obtained at the 8m Gemini and 6.5m MMT reveal
peak-to-peak radial velocity variations of 400 km/s every 20 min for the WD,
but no velocity variations for the M dwarf. In addition, high-speed photometry
from the McDonald 2.1m telescope shows no evidence of variability nor evidence
of a reflection effect. An M dwarf companion is physically too large to fit
into a 20 min orbit. Thus, the orbital motion of the WD is almost certainly due
to an invisible WD companion. The M dwarf must be either an unrelated
background object or the tertiary component of a hiearchical triple system.
WD0931+444 contains a pair of WDs, a 0.32 Msol primary and a >0.14 Msol
secondary, at a separation of >0.19 Rsol. After J0651+2844, WD0931+444 becomes
the second-shortest period detached binary WD currently known. The two WDs will
lose angular momentum through gravitational wave radiation and merge in <9 Myr.
The log h ~ -22 gravitational wave strain from WD0931+444 is strong enough to
make it a verification source for gravitational wave missions in the
milli-Hertz frequency range, e.g. the evolved Laser Interferometer Space
Antenna (eLISA), bringing the total number of known eLISA verification sources
to nine.Comment: MNRAS Letters, in pres
The science benefits of and the antenna requirements for microwave remote sensing from geostationary orbit
The primary objective of the Large Space Antenna (LSA) Science Panel was to evaluate the science benefits that can be realized with a 25-meter class antenna in a microwave/millimeter wave remote sensing system in geostationary orbit. The panel concluded that a 25-meter or larger antenna in geostationary orbit can serve significant passive remote sensing needs in the 10 to 60 GHz frequency range, including measurements of precipitation, water vapor, atmospheric temperature profile, ocean surface wind speed, oceanic cloud liquid water content, and snow cover. In addition, cloud base height, atmospheric wind profile, and ocean currents can potentially be measured using active sensors with the 25-meter antenna. Other environmental parameters, particularly those that do not require high temporal resolution, are better served by low Earth orbit based sensors
Sloan Digital Sky Survey Spectroscopic Lens Search. I. Discovery of Intermediate-Redshift Star-Forming Galaxies Behind Foreground Luminous Red Galaxies
We present a catalog of 49 spectroscopic strong gravitational lens candidates
selected from a Sloan Digital Sky Survey sample of 50996 luminous red galaxies.
Potentially lensed star-forming galaxies are detected through the presence of
background oxygen and hydrogen nebular emission lines in the spectra of these
massive foreground galaxies. This multiline selection eliminates the ambiguity
of single-line identification and provides a very promising sample of candidate
galaxy-galaxy lens systems at low to intermediate redshift, with foreground
redshifts ranging from 0.16 to 0.49 and background redshifts from 0.25 to 0.81.
Any lenses confirmed within our sample would be important new probes of
early-type galaxy mass distributions, providing complementary constraints to
those obtained from currently known lensed high-redshift quasars.Comment: 23 pages; to appear in The Astronomical Journal, 2004 April. Version
with full-resolution figures available at
http://web.mit.edu/bolton/www/speclens.ps.gz (PostScript) or
http://web.mit.edu/bolton/www/speclens.pdf (PDF
Proverb comprehension in individuals with agenesis of the corpus callosum
Comprehension of non-literal language involves multiple neural systems likely involving callosal connections. We describe proverb comprehension impairments in individuals with isolated agenesis of the corpus callosum (AgCC) and normal-range general intelligence. Experiment 1 compared Gorham Proverb Test (Gorham, 1956) performance in 19 adults with AgCC and 33 neurotypical control participants of similar age, sex, and intelligence. Experiment 2 used the Proverbs subtest of the Delis-Kaplan Executive Function System (D-KEFS, 2001) to compare 19 adults with AgCC and 17 control participants with similar age, sex, and intelligence. Gorham Proverbs performance was impaired in the AgCC group for both the free-response and multiple-choice tasks. On the D-KEFS proverbs test, the AgCC group performed significantly worse on the free-response task (and all derivative scores) despite normal levels of performance on the multiple-choice task. Covarying verbal intelligence did not alter these outcomes. However, covarying a measure of non-literal language comprehension considerably reduced group differences in proverb comprehension on the Gorham test, but had little effect on the D-KEFS group differences. The difference between groups seemed to be greatest when participants had to generate their own interpretation (free response), or in the multiple choice format when the test included many proverbs that were likely to be less familiar. Taken together, the results of this study clearly show that proverb comprehension is diminished in individuals with AgCC compared to their peers
Spectroscopic Observations of Hot Lines Constraining Coronal Heating in Solar Active Regions
EUV observations of warm coronal loops suggest that they are bundles of
unresolved strands that are heated impulsively to high temperatures by
nanoflares. The plasma would then have the observed properties (e.g., excess
density compared to static equilibrium) when it cools into the 1-2 MK range. If
this interpretation is correct, then very hot emission should be present
outside of proper flares. It is predicted to be vey faint, however. A critical
element for proving or refuting this hypothesis is the existence of hot, very
faint plasmas which should be at amounts predicted by impulsive heating. We
report on the first comprehensive spectroscopic study of hot plasmas in active
regions. Data from the EIS spectrometer on Hinode were used to construct
emission measure distributions in quiescent active regions in the 1-5 MK
temperature range. The distributions are flat or slowly increasing up to
approximately 3 MK and then fall off rapidly at higher temperatures. We show
that active region models based on impulsive heating can reproduce the observed
EM distributions relatively well. Our results provide strong new evidence that
coronal heating is impulsive in nature.Comment: ApJ, 2009, in pres
PET and P300 Relationships in Early Alzheimer\u27s Disease
The P300 (P3) wave of the auditory brain event-related potential was investigated in patients with probable Alzheimer\u27s disease to determine whether P300 latency discriminated these patients from controls and whether prolonged P300 latency correlated with rates of brain glucose metabolism as measured by Positron Emission Tomography. P300 latency was prolonged by more than 1.5 standard deviations from age expectancy in 14 of 18 patients, but none of 17 controls. In these subjects P300 latency was shown to be inversely correlated with relative metabolic rates of parietal and, to a lesser extent, temporal and frontal association areas, but not with subcortical areas
Verbal learning and memory in agenesis of the corpus callosum
The role of interhemispheric interactions in the encoding, retention, and retrieval of verbal memory can be clarified by assessing individuals with complete or partial agenesis of the corpus callosum (AgCC), but who have normal intelligence. This study assessed verbal learning and memory in AgCC using the California Verbal Learning Test—Second Edition (CVLT-II). Twenty-six individuals with AgCC were compared to 24 matched controls on CVLT-II measures, as well as Donders׳ four CVLT-II factors (i.e., Attention Span, Learning Efficiency, Delayed Memory, and Inaccurate Memory). Individuals with AgCC performed significantly below healthy controls on the Delayed Memory factor, confirmed by significant deficits in short and long delayed free recall and cued recall. They also performed less well in original learning. Deficient performance by individuals with AgCC during learning trials, as well as deficits in all forms of delayed memory, suggest that the corpus callosum facilitates interhemispheric elaboration and encoding of verbal information
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