788 research outputs found
X-ray spectral and timing properties of the 2001 superburst of 4U 1636-536
Preliminary results are reported on the spectral and timing properties of the
spectacular 2001 superburst of 4U 1636-536 as seen by the RXTE/PCA. The
(broad-band) power-spectral and hardness properties during the superburst are
compared to those just before and after the superburst. Not all of the
superburst emission can be fitted by pure black-body radiation. We also
gathered BeppoSAX/WFC and RXTE/ASM data, as well as other RXTE/PCA data,
obtained days to months before and after the superburst to investigate the
normal X-ray burst behavior around the time of the superburst. The first normal
X-ray burst after the 2001 superburst was detected 23 days later. During
inspection of all the RXTE/ASM data we found a third superburst. This
superburst took place on June 26, 1999, which is ~2.9 yrs after the 1996
superburst and ~1.75 yrs before the 2001 superburst. The above findings are the
strongest constraints observed so far on the duration of the cessation of
normal X-ray bursts after a superburst and the superburst recurrence times.Comment: 4 pages, 4 figures,to appear in the proceedings of "X-Ray Timing
2003: Rossi and Beyond", eds. P. Kaaret, F.K. Lamb, & J.H. Swank (Melville,
NY: AIP
Infratentorial Abnormalities in Vascular Dementia
Background and Purpose—Infratentorial abnormalities may cause cognitive deficits, but current research criteria for
vascular dementia (VaD) do not consider them. Our purposes were to determine the prevalence of infratentorial
abnormalities in VaD, their relation with supratentorial abnormalities, and whether they are relevant to cognition.
Methods—We examined 182 patients (120 men, mean age 73 years, SD 8) with probable VaD at inclusion into a
multicenter clinical trial. MRI scans were evaluated for infratentorial vascular abnormalities, midbrain atrophy,
cerebellar atrophy, basilar artery diameter and tortuosity, and supratentorial abnormalities. Cognitive testing included
the mini–mental state examination (MMSE) and the vascular dementia assessment scale (VaDAS-cog).
Results—One hundred forty-one (77.5%) patients had infratentorial abnormalities: 119 (65.4%) had focal infratentorial
vascular lesions, 65 (35.7%) had diffuse pontine vascular abnormalities hyperintense on T2-weighted images, 20
(11.0%) had midbrain atrophy, and 16 (8.8%) had cerebellar atrophy. Significant correlations were found between
number of infratentorial vascular lesions and basilar artery diameter (rs 0.26; P 0.0001), infratentorial and basal
ganglia (including thalamus) vascular abnormalities (rs 0.30; P 0.0001), as well as between midbrain atrophy and
global supratentorial atrophy (rs 0.27; P 0.0001). Infratentorial vascular abnormalities and cerebellar atrophy were not
significantly associated with cognitive impairment. Patients with midbrain atrophy performed worse on cognitive tests
than those without midbrain atrophy. After correction for sex, age, education, supratentorial abnormalities, and center,
midbrain atrophy remained significantly associated with lower MMSE scores (P 0.05).
Conclusions—Infratentorial abnormalities often occur in patients with VaD, but only midbrain atrophy was found to be
relevant to cognitio
Purification, crystallization and preliminary X-ray analysis of the lytic transglycosylase MltA from Escherichia coli
The lytic transglycosylase MltA from Escherichia coli with its membrane anchor and signal sequence deleted has been purified to homogeneity by means of cation-exchange chromatography. The enzyme was crystallized using the hanging-drop vapour-diffusion method. The crystals belong to space group P3(1)21 or P3(2)21, with unit-cell parameters a=b=103.70, c=109.84 Angstrom and one molecule per asymmetric unit. Crystals diffract to 2.2 Angstrom resolution on a synchrotron-radiation source
Meeting your match: How attractiveness similarity affects approach behavior in mixed-sex dyads
Item does not contain fulltextThis experimental study investigated approach behavior toward opposite-sex others of similar versus dissimilar physical attractiveness. Furthermore, it tested the moderating effects of sex. Single participants interacted with confederates of high and low attractiveness. Observers rated their behavior in terms of relational investment (i.e., behavioral efforts related to the improvement of interaction fluency, communication of positive interpersonal affect, and positive self-presentation). As expected, men displayed more relational investment behavior if their own physical attractiveness was similar to that of the confederate. For women, no effects of attractiveness similarity on relational investment behavior were found. Results are discussed in the light of positive assortative mating, preferences for physically attractive mates, and sex differences in attraction-related interpersonal behaviors.13 p
Thalamic Lesions in Vascular Dementia: Low Sensitivity of Fluid-Attenuated Inversion Recovery (FLAIR) Imaging
Background and Purpose—The criteria of the National Institute of Neurological Disorders and Stroke (NINDS)–
Association Internationale pour la Recherche et l’Enseignement en Neurosciences (AIREN) include thalamic lesions for
the diagnosis of vascular dementia (VaD). Although studies concerning VaD and brain aging advocate the use of
fluid-attenuated inversion recovery (FLAIR) or T2-weighted images (T2-WI) to detect ischemic lesions, none compared
the sensitivity of these sequences to depict thalamic lesions.
Methods—We performed a blinded review of T2-WI and FLAIR images in 73 patients fulfilling the radiological part of the NINDS-AIREN criteria (mean age, 71 years; range, 49 to 83 years). This sample was drawn from a large multicenter trial on VaD and was expected to have a high prevalence of thalamic lesions. In a side-by-side review, including T1-weighted images as well, lesions were classified according to presumed underlying pathology.
Results—The total number of thalamic lesions was 214. Two hundred eight (97%) were detected on T2-WI, but only 117
(55%) were detected on FLAIR ( 2 5.1; P 0.05). Although the mean size of lesions detected on T2-WI and not on FLAIR (4.4 mm) was significantly lower than the mean size of lesions detected on both sequences (6.7 mm) (P 0.001), 5 of the 29 lesions 10 mm on T2-WI were not visible on FLAIR. FLAIR detected only 81 (51%) of the 158 probable ischemic lesions and 30 (60%) of the 50 probable microbleeds.
Conclusions—FLAIR should not be used as the only T2-weighted sequence to detect thalamic lesions in patients suspected
of having VaD
The atoll source states of 4U 1608-52
We have studied the atoll source 4U 1608-52 using a large data set obtained
with the Rossi X-ray Timing Explorer. We find that the timing properties of 4U
1608-52 are almost exactly identical to those of the atoll sources 4U 0614+09
and 4U 1728-34 despite the fact that contrary to these sources 4U 1608-52 is a
transient covering two orders of magnitude in luminosity. The frequencies of
the variability components of these three sources follow a universal scheme
when plotted versus the frequency of the upper kilohertz QPO, suggesting a very
similar accretion flow configuration. If we plot the Z sources on this scheme
only the lower kilohertz QPO and HBO follow identical relations. Using the
mutual relations between the frequencies of the variability components we
tested several models; the transition layer model, the sonic point beat
frequency model, and the relativistic precession model. None of these models
described the data satisfactory. Recently, it has been suggested that the atoll
sources (among them 4U 1608-52) trace out similar three-branch patterns as the
Z sources in the color-color diagram. We have studied the relation between the
power spectral properties and the position of 4U 1608-52 in the color-color
diagram and conclude that the timing behavior is not consistent with the idea
that 4U 1608-52 traces out a three-branched Z shape in the color-color diagram
along which the timing properties vary gradually, as Z sources do.Comment: 43 pages, 16 figures, ApJ accepte
Peculiar spectral and power spectral behaviour of the LMXB GX 13+1
We present results of an analysis of all 480 ks of Rossi X-ray Timing
Explorer Proportional Counter Array data obtained from 17 May 1998 to 11
October 1998 on the luminous low mass X-ray binary GX 13+1. We analysed the
spectral properties in colour-colour diagrams (CDs) and hardness-intensity
diagrams (HIDs) and fitted the power spectra with a multi-Lorentzian model. GX
13+1 traces out a curved track in the CDs on a time scale of hours, which is
very reminiscent of a standard atoll track containing an island, and lower and
upper banana branch. However, both count rate and power spectral properties
vary along this track in a very unusual way, not seen in any other atoll or Z
source. The count rate, which varied by a factor of ~1.6, along a given track
first decreases and then increases, causing the motion through the HIDs to be
in the opposite sense to that in the CD, contrary to all other Z and atoll
sources. Along a CD track, the very low frequency noise uniquely decreases in
amplitude from ~5 to ~2% (rms). The high frequency noise amplitude decreases
from ~4% to less than 1% and its characteristic frequency decreases from ~10 to
\~5 Hz. The 57-69 Hz quasi-periodic oscillation (QPO) found earlier is also
detected, and no kHz QPOs are found. In addition the entire track shows secular
motion on a time scale of about a week. The average count rate as well as the
amplitude of the very low frequency noise correlate with this secular motion.
We discuss a possible explanation for the peculiar properties of GX 13+1 in
terms of an unusual orientation or strength of a relativistic jet.Comment: 15 pages, 13 figures. Accepted for publication in A&
Millihertz Quasi-periodic Optical Oscillations in 4U 0614+091
We report the discovery of a 1mHz optical quasi-periodic oscillation (QPO) in
the candidate ultracompact low-mass X-ray binary 4U 0614+091. The ultra-low
frequency QPO has no X-ray counterpart in contemporaneous RXTE/PCA data and is
likely a signature of structure in the accretion disk. The QPO can be
reasonably fitted with a single sine wave but with a phase jump part way
through the observation, indicating that it is not coherent.We also identify a
48 min modulation, approximately consistent with the suggested orbital period
of O'Brien (2005) and Shahbaz et al. (2008). If this is indeed orbital, it
supports an identification of 4U 0614+091 as an ultra-compact source.Comment: 7 pages, 5 figures, accepted for publication in Monthly Notices of
the Royal Astronomical Societ
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