779 research outputs found
The 2006 Outburst of the Magnetar CXOU J164710.2-455216
We report on data obtained with the Chandra, XMM-Newton, Suzaku and Swift
X-ray observatories, following the 2006 outburst of the Anomalous X-ray Pulsar
CXO J164710.2-455216. We find no evidence for the very large glitch and rapid
exponential decay as was reported previously for this source. We set a 3 sigma
upper limit on any fractional frequency increase at the time of the outburst of
Delta nu/nu < 1.5 x 10^{-5}. Our timing analysis, based on the longest time
baseline yet, yields a spin-down rate for the pulsar that implies a surface
dipolar magnetic field of ~9 x 10^{13} G, although this could be biased high by
possible recovery from an undetected glitch. We also present an analysis of the
source flux and spectral evolution, and find no evidence for long-term spectral
relaxation post-outburst as was previously reported.Comment: Submitted to Ap
Effects of physiological arousal on speech motor control and speech motor practice in preschool-age children who do and do not stutter
Purpose: We examined the effects of physiological arousal on speech motor control and speech motor practice effects in preschool-age children who do (CWS) and do not stutter (CWNS). Method: Participants included 18 CWS (mean age 4 years, 5 months) and 18 age- and gender-matched CWNS. The participants repeated a phrase “buy bobby a puppy” interspersed with viewing pictures from the International Affective Picture System under two experimental conditions speaking after viewing pictures with (1) negative, and (2) neutral valence. Participants’ lip movements were tracked using Optotrak system. The spatio-temporal index (STI; Smith, Goffman, Zelaznik, Ying & McGillem, 1995) and mean utterance duration were calculated to examine speech motor control and speech motor practice effects. Skin conductance level was measured during the experimental conditions to assess participants’ physiological level of arousal. Results: Preschool-age CWS demonstrated greater speech movement variability across all conditions and trials than CWNS. Further, the younger participants produced more variable articulatory movements than the older participants. Participants’ speech movement variability did not significantly differ between the negative and neutral experimental conditions and the level of physiological arousal did not have a significant effect on it. There was a non-significant trend of decrease in speech movement variability across the repeated trials in both groups. Last, CWS and CWNS did not differ in their mean utterance duration, suggesting that their articulation rate was similar across all conditions and trials. Conclusions: Our findings indicate that, compared to preschool-age CWNS, CWS demonstrate less mature speech motor control. However, present findings do not support the hypothesis that CWS benefit less from motor practice relative to CWNS. Given that our conditions elicited similar levels of arousal in the participants, future research is needed to examine whether physiological arousal disrupts speech motor control in preschool-age children potentially contributing to disruptions of speech fluency and the development of stuttering
The Role of Behavioral Inhibition for Conversational Speech and Language Characteristics of Preschool-Age Children Who Stutter
X-ray and Near-IR Variability of the Anomalous X-ray Pulsar 1E 1048.1-5937: From Quiescence Back to Activity
(Abridged) We report on new and archival X-ray and near-infrared observations
of the anomalous X-ray pulsar 1E 1048.1-5937 performed between 2001-2007 with
RXTE, CXO, Swift, HST, and VLT. During its ~2001-2004 active period, 1E
1048.-5937 exhibited two large, long-term X-ray pulsed-flux flares as well as
short bursts, and large (>10x) torque changes. Monitoring with RXTE revealed
that the source entered a phase of timing stability in 2004; at the same time,
a series of four simultaneous observations with CXO and HST in 2006 showed that
its X-ray flux and spectrum and near-IR flux, all variable prior to 2005,
stabilized. The near-IR flux, when detected by HST (H~22.7 mag) and VLT
(K_S~21.0 mag), was considerably fainter than previously measured. Recently, in
2007 March, this newfound quiescence was interrupted by a sudden flux
enhancement, X-ray spectral changes and a pulse morphology change, simultaneous
with a large spin-up glitch and near-IR enhancement. Our RXTE observations
revealed a sudden pulsed flux increase by a factor of ~3 in the 2-10 keV band.
In observations with CXO and Swift, we found that the total X-ray flux
increased much more than the pulsed flux, reaching a peak value of >7 times the
quiescent value (2-10 keV). With these recent data, we find a strong
anti-correlation between X-ray flux and pulsed fraction, and a correlation
between X-ray spectral hardness and flux. Simultaneously with the radiative and
timing changes, we observed a significant X-ray pulse morphology change such
that the profile went from nearly sinusoidal to having multiple peaks. We
compare these remarkable events with other AXP outbursts and discuss
implications in the context of the magnetar model and other models of AXP
emission.Comment: 13 pages (6 figures) in emulateapj style. Accepted for publication in
ApJ. New version includes referee's corrections; split Figure 1 into 2
figures; modified Figs. 4b and 6b; rearranged and renumbered of some figures
and sections; added an X-ray dataset; improved analysis of pulse morphology
and pulsed fraction; added paragraph to sec. 3.2.
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Viability of Non-Coplanar VMAT for Liver SBRT as Compared to Coplanar VMAT and Beam Orientation Optimized 4Ď€ IMRT.
PurposeThe 4Ď€ static non-coplanar radiotherapy delivery technique has demonstrated better normal tissue sparing and dose conformity than the clinically used volumetric modulated arc therapy (VMAT). It is unclear whether this is a fundamental limitation of VMAT delivery or the coplanar nature of its typical clinical plans. The dosimetry and the limits of normal tissue toxicity constrained dose escalation of coplanar VMAT, non-coplanar VMAT and 4Ď€ radiotherapy are quantified in this study.Methods and materialsClinical stereotactic body radiation therapy plans for 20 liver patients receiving 30-60 Gy using coplanar VMAT (cVMAT) were re-planned using 3-4 partial non-coplanar arcs (nVMAT) and 4Ď€ with 20 intensity-modulated non-coplanar fields. The conformity number (CN), homogeneity index (HI), 50% dose spillage volume (R50), normal liver volume receiving >15 Gy (VL>15), dose to organs at risk (OARs), and tumor control probability (TCP) were compared for all three treatment plans. The maximum tolerable dose (MTD) yielding a normal liver normal tissue control probability (NTCP) below 1%, 5%, and 10% was calculated with the Lyman-Kutcher-Burman model for each plan, as well as the resulting survival fractions at one, two, three, and four years.ResultsCompared to cVMAT, the nVMAT and 4Ď€ plans reduced VL>15 by an average of 5 cm3 and 80 cm3, respectively. 4Ď€ reduced the 50% dose spillage volume by ~23% compared to both VMAT plans, and either significantly decreased or maintained OAR doses. The 4Ď€ MTDs and survival fractions were significantly higher than both cVMAT and nVMAT (p<0.05) for all normal liver NTCP limits used in this study.ConclusionsThe 4Ď€ technique provides significantly better OAR sparing than both cVMAT and vMAT and enables more clinically relevant dose escalation for tumor local control. Therefore, despite the current accessibility of nVMAT, it is not a viable alternative to 4Ď€ for liver SBRT
A Burst and Simultaneous Short-Term Pulsed Flux Enhancement from the Magnetar Candidate 1E 1048.1-5937
We report on the 2004 June 29 burst detected from the direction of the
Anomalous X-ray Pulsar (AXP) 1E 1048.1-5937 using the Rossi X-ray Timing
Explorer (RXTE). We find a simultaneous increase of ~3.5 times the quiescent
value in the 2-10 keV pulsed flux of 1E 1048.1-5937 during the tail of the
burst which identifies the AXP as the burst's origin. The burst was overall
very similar to the two others reported from the direction of this source in
2001. The unambiguous identification of 1E 1048.1-5937 as the burster here
confirms it was the origin of the 2001 bursts as well. The epoch of the burst
peak was very close to the arrival time of 1E 1048.1-5937's pulse peak. The
burst exhibited significant spectral evolution with the trend going from hard
to soft. During the 11 days following the burst, the AXP was observed further
with RXTE, XMM-Newton and Chandra. Pre- and post-burst observations revealed no
change in the total flux or spectrum of the quiescent emission. Comparing all
three bursts detected thus far from this source we find that this event was the
most fluent (>3.3x10^-8 erg/cm^2 in the 2-20 keV band), had the highest peak
flux (59+/-9x10^-10 erg/s/cm^2 in the 2-20 keV band), and the longest duration
(>699 s). The long duration of the burst differentiates it from Soft Gamma
Repeater (SGR) bursts which have typical durations of ~0.1 s. Bursts that occur
preferentially at pulse maximum, have fast-rises and long X-tails containing
the majority of the total burst energy have been seen uniquely from AXPs. The
marked differences between AXP and SGRs bursts may provide new clues to help
understand the physical differences between these objects.Comment: 24 pages, 4 figures, submitted to the Astrophysical Journa
Engage Me: Using New Literacies to Create Third Space Classrooms that Engage Student Writers
Adolescents use a wide variety of literacy practices in their daily lives. Preservice teachers in this study looked for ways to motivate their students to write by asking them about their in-school and out-of-school writing practices. This survey shows a gap between what motivates students to write for school and why they write out of school. The results suggest that English teachers can forge a “third space” in which out-of-school literacy practices are integrated into the curriculum. This survey provides insights for improving writing pedagogy in regards to students’ expressed desire to communicate, express themselves, and to be involved
The Pulsed Spectra of Two Extraordinary Pulsars
We report on X-ray monitoring of two isolated pulsars within the same RXTE
field of view. PSR J1811-1925 in the young supernova remnant G11.2-0.3 has a
nearly sinusoidal pulse profile with a hard pulsed spectrum (photon index
\~1.2). The pulsar is a highly efficient (~ 1% of spin-down energy) emitter of
2-50 keV pulsed X-rays despite having a fairly typical B ~ 2e12 G magnetic
field. PSR J1809-1943/XTE J1810-197 is a newly discovered slow (P=5.54 s),
apparently isolated X-ray pulsar which increased in flux by a factor of ~100 in
2003 January. Nine months of monitoring observations have shown a decrease in
pulsed flux of ~ 30% without a significant change in its apparently thermal
spectrum (kT ~0.7 keV) or pulse profile. During this time, the spin-down torque
has fluctuated by a factor of ~ 2. Both the torque and the flux have remained
steady for the last 3 months, at levels consistent with a magnetar
interpretation.Comment: 3 pages, 4 figures, to appear in the Proceedings of X-ray Timing
2003: Rossi and Beyond, ed. P. Kaaret, F.K. Lamb, & J.H. Swank held in
Cambridge, MA, Nov. 3-5, 200
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