18,740 research outputs found
Reply to comment by H. Hasegawa on "Evolution of Kelvin-Helmholtz activity on the dusk flank magnetopause"
We demonstrate, on experimental grounds, that the justifications for the comment by Hasegawa [2009], hereinafter
H09, on work done by Foullon et al. [2008], hereinafter F08, are not well founded
An X-ray and Optical Investigation of the Environments Around Nearby Radio Galaxies
Investigations of the cluster environment of radio sources have not shown a
correlation between radio power and degree of clustering. However, it has been
demonstrated that extended X-ray luminosity and galaxy clustering do exhibit a
positive correlation. This study investigates a complete sample of 25 nearby (z
less than 0.06) radio galaxies which are not cataloged members of Abell
clusters. The environment of these radio galaxies is studied in both the X-ray
and the optical by means of the ROSAT All-Sky Survey (RASS), ROSAT pointed
observations, and the Palomar optical Digitized Sky Survey (DSS). X-ray
luminosities and extents are determined from the RASS, and the DSS is used to
quantify the degree of clustering via the spatial two-point correlation
coefficient, Bgg. Of the 25 sources, 20 are greater than sigma detections in
the X-ray and 11 possessed Bgg's significantly in excess of that expected for
an isolated galaxy. Adding the criterion that the X-ray emission be resolved,
10 of the radio galaxies do appear to reside in poor clusters with extended
X-ray emission suggestive of the presence of an intracluster medium. Eight of
these galaxies also possess high spatial correlation coefficients. Taken
together, these data suggest that the radio galaxies reside in a low richness
extension of the Abell clusters. The unresolved X-ray emission from the other
galaxies is most likely associated with AGN phenomena. Furthermore, although
the sample size is small, it appears that the environments of FR I and FR II
sources differ. FR I's tend to be more frequently associated with extended
X-ray emission (10 of 18), whereas FR II's are typically point sources or
non-detections in the X-ray (none of the 7 sources exhibit extended X-ray
emission).Comment: 28 page postscript file including figures and tables, plus one
landscape table and 5 GIF figure
Time-resolved energy transfer from single chloride terminated nanocrystals to graphene
We examine the time-resolved resonance energy transfer of excitons from
single n-butyl amine-bound, chloride-terminated nanocrystals to two-dimensional
graphene through time-correlated single photon counting. The radiative
biexponential lifetime kinetics and blinking statistics of the individual
surface-modified nanocrystal elucidate the non-radiative decay channels.
Blinking modification as well as a 4 times reduction in spontaneous emission
were observed with the short chloride and n-butylamine ligands, probing the
energy transfer pathways for the development of graphene-nanocrystal
nanophotonic devices
Cluster observations of the midaltitude cusp under strong northward interplanetary magnetic field
We report on a multispacecraft cusp observation lasting more than 100 min. We
determine the cusp boundary motion and reveal the effect on the cusp size of the
interplanetary magnetic field (IMF) changing from southward to northward. The cusp
shrinks at the beginning of the IMF rotation and it reexpands at the rate of 0.40°
invariant latitude per hour under stable northward IMF. On the basis of plasma signatures
inside the cusp, such as counterstreaming electrons with balanced fluxes, we propose
that pulsed dual lobe reconnection operates during the time of interest. SC1 and
SC4 observations suggest a long-term regular periodicity of the pulsed dual reconnection,
which we estimate to be ~1–5 min. Further, the distances from the spacecraft to
the reconnection site are estimated on the basis of observations from three satellites. The
distance determined using SC1 and SC4 observations is ~15 RE and that determined
from SC3 data is ~8 RE. The large-scale speed of the reconnection site sunward motion is
~16 km s-1. We observe also a fast motion of the reconnection site by SC1, which
provides new information about the transitional phase after the IMF rotation. Finally, a
statistical study of the dependency of plasma convection inside the cusp on the IMF clock
angle is performed. The relationship between the cusp stagnation, the dual lobe
reconnection process, and the IMF clock angle is discussed
Cognitive performance in multiple system atrophy
The cognitive performance of a group of patients with multiple system atrophy (MSA) of striato-nigral predominance was compared with that of age and IQ matched control subjects, using three tests sensitive to frontal lobe dysfunction and a battery sensitive to memory and learning deficits in Parkinson's disease and dementia of the Alzheimer type. The MSA group showed significant deficits in all three of the tests previously shown to be sensitive to frontal lobe dysfunction. Thus, a significant proportion of patients from the MSA group failed an attentional set-shifting test, specifically at the stage when an extra-dimensional shift was required. They were also impaired in a subject-ordered test of spatial working memory. The MSA group showed deficits mostly confined to measures of speed of thinking, rather than accuracy, on the Tower of London task. These deficits were seen in the absence of consistent impairments in language or visual perception. Moreover, the MSA group showed no significant deficits in tests of spatial and pattern recognition previously shown to be sensitive to patients early in the course of probable Alzheimer's disease and only a few patients exhibited impairment on the Warrington Recognition Memory Test. There were impairments on other tests of visual memory and learning relative to matched controls, but these could not easily be related to fundamental deficits of memory or learning. Thus, on a matching-to-sample task the patients were impaired at simultaneous but not delayed matching to sample, whereas difficulties in a pattern-location learning task were more evident at its initial, easier stages. The MSA group showed no consistent evidence of intellectual deterioration as assessed from their performance on subtests of the Wechsler Adult Intelligence Scale (WAIS) and the National Adult Reading Test (NART). Consideration of individual cases showed that there was some heterogeneity in the pattern of deficits in the MSA group, with one patient showing no impairment, even in the face of considerable physical disability. The results show a distinctive pattern of cognitive deficits, unlike those previously seen using the same tests in patients with Parkinson's and Alzheimer's diseases, and suggesting a prominent frontal-lobe-like component. The implications for concepts of 'subcortical' dementia and 'fronto-striatal' cognitive dysfunction are considered
A Comprehensive Radio and Optical Study of Abell 2256: Activity from an Infalling Group
Abell 2256 is a nearby (z~0.06), rich cluster of galaxies with fascinating
observed properties across a range of wavelengths. Long believed to represent a
cluster merger, recent X-ray and optical results have suggested that in
addition to the primary cluster and subcluster there is evidence for a third,
poorer system. We present wide-field, high sensitivity 1.4 GHz VLA radio
observations of Abell 2256 in conjunction with optical imaging and additional
spectroscopy. Over 40 cluster radio galaxies are identified, with optical
spectroscopy indicating the emission source (star formation or AGN) for most of
them. While the overall fraction of galaxies exhibiting radio emission is
consistent with a large sample of other nearby clusters, we find an increase in
the activity level of galaxies belonging to the third system (hereafter, the
``Group''). Specifically, the Group has relatively more star formation than
both the primary cluster and main subcluster. The position of the Group is also
coincident with the observed cluster radio relic. We suggest that the Group
recently (~0.3 Gyr) merged with the primary cluster and that this merger, not
the ongoing merger of the primary and the main subcluster, might be responsible
for many of the unusual radio properties of Abell 2256. Furthermore, the
greater star formation activity of the Group suggests that the infall of groups
is an important driver of galaxy evolution in clusters.Comment: 21 pages plus 13 JPEG figures; to appear in the Astronomical Journa
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