41,442 research outputs found
Pursuing the planet-debris disk connection: Analysis of upper limits from the Anglo-Australian Planet Search
Solid material in protoplanetary discs will suffer one of two fates after the
epoch of planet formation; either being bound up into planetary bodies, or
remaining in smaller planetesimals to be ground into dust. These end states are
identified through detection of sub-stellar companions by periodic radial
velocity (or transit) variations of the star, and excess emission at mid- and
far-infrared wavelengths, respectively. Since the material that goes into
producing the observable outcomes of planet formation is the same, we might
expect these components to be related both to each other and their host star.
Heretofore, our knowledge of planetary systems around other stars has been
strongly limited by instrumental sensitivity. In this work, we combine
observations at far-infrared wavelengths by IRAS, Spitzer, and Herschel with
limits on planetary companions derived from non-detections in the 16-year
Anglo-Australian Planet Search to clarify the architectures of these
(potential) planetary systems and search for evidence of correlations between
their constituent parts. We find no convincing evidence of such correlations,
possibly owing to the dynamical history of the disk systems, or the greater
distance of the planet-search targets. Our results place robust limits on the
presence of Jupiter analogs which, in concert with the debris disk
observations, provides insights on the small-body dynamics of these nearby
systems.Comment: Accepted for publication in A
Discovery of a Spin-Down State Change in the LMC Pulsar B0540-69
We report the discovery of a large, sudden, and persistent increase in the
spin-down rate of B0540-69, a young pulsar in the Large Magellanic Cloud, using
observations from the Swift and RXTE satellites. The relative increase in the
spin-down rate of 36% is unprecedented for B0540-69. No accompanying change in
the spin rate is seen, and no change is seen in the pulsed X-ray emission from
B0540-69 following the change in the spin-down rate. Such large relative
changes in the spin-down rate are seen in the recently discovered class of
'intermittent pulsars', and we compare the properties of B0540-69 to such
pulsars. We consider possible changes in the magnetosphere of the pulsar that
could cause such a large change in the spin-down rate.Comment: 6 pages, 2 figures, accepted for publication in ApJ Letter
Switching modalities in a sentence verification task: ERP evidence for embodied language processing
In an event related potential (ERP) experiment using written language materials only, we investigated a potential modulation of the N400 by the modality switch effect. The modality switch effect occurs when a first sentence, describing a fact grounded in one modality, is followed by a second sentence describing a second fact grounded in a different modality. For example, "A cellar is dark" (visual), was preceded by either another visual property "Ham is pink" or by a tactile property "A mitten is soft." We also investigated whether the modality switch effect occurs for false sentences ("A cellar is light"). We found that, for true sentences, the ERP at the critical word "dark" elicited a significantly greater frontal, early N400-like effect (270370 ms) when there was a modality mismatch than when there was a modality-match. This pattern was not found for the critical word "light" in false sentences. Results similar to the frontal negativity were obtained in a late time window (500700 ms). The obtained ERP effect is similar to one previously obtained for pictures. We conclude that in this paradigm we obtained fast access to conceptual properties for modality-matched pairs, which leads to embodiment effects similar to those previously obtained with pictorial stimuli
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The effect of dyslexia on information retrieval: A pilot study
Purpose – The purpose of the paper is to resolve a gap in our knowledge of how people with dyslexia interact with Information Retrieval (IR) systems, specifically an understanding of their information searching behaviour. Very little research has been undertaken with this particular user group, and given the size of the group (an estimated 10% of the population) this lack of knowledge needs to be addressed.
Design/Methodology/Approach - We use elements of the dyslexia cognitive profile to design a logging system recording the difference between two sets of participants: dyslexic and control users. We use a standard Okapi interface together with two standard TREC topics in order to record the information searching behaviour of these users. We gather evidence from various sources, including quantitative information on search logs, together with qualitative information from interviews and questionnaires. We record variables on queries, documents, relevance assessments and sessions in the search logs. We use this evidence to examine the difference in searching between the two sets of users, in order to understand the effect of dyslexia on the information searching behaviour. A topic analysis is also conducted on the quantitative data to show any effect on the results from the information need.
Research limitations/implications – As this is a pilot study, only 10 participants were recruited for the study, 5 for each user group. Due to ethical issues, the number of topics per search was restricted to one topic only. The study shows that the methodology applied is useful for distinguishing between the two user groups, taking into account differences between topic. We outline further research on the back of this pilot study in four main areas. A different approach from the proposed methodology is needed to measure the effect on query variables, which takes account of topic variation. More details on users are needed such as reading abilities, speed of language processing and working memory to distinguish the user groups. Effect of topic on search interaction must be measured in order to record the potential impact on the dyslexic user group. Work is needed on relevance assessment and effect on precision and recall for users who may not read many documents.
Findings – Using the log data, we establish the differences in information searching behaviour of control and dyslexic users i.e. in the way the two groups interact with Okapi, and that qualitative information collected (such as experience etc) may not be able to account for these differences. Evidence from query variables was unable to distinguish between groups, but differences on topic for the same variables were recorded. Users who view more documents tended to judge more documents as being relevant, either in terms of the user group or topic. Session data indicated that there may be an important difference between the number of iterations used in a search between the user groups, as there may be little effect from the topic on this variable.
Originality/Value – This is the first study of the effect of dyslexia on information search behaviour, and provides some evidence to take the field forward
CP nonconservation in the leptonic sector
In this paper we use an exact method to impose unitarity on moduli of
neutrino PMNS matrix recently determined, and show how one could obtain
information on CP nonconservation from a limited experimental information. One
suggests a novel type of global fit by expressing all theoretical quantities in
terms of convention independent parameters: the Jarlskog invariant and the
moduli , able to resolve the positivity problem of .
In this way the fit will directly provide a value for , and if it is
different from zero it will prove the existence of CP violation in the
available experimental data. If the best fit result, , from M.
Maltoni {\em et al}, [New J.Phys. {\bf 6} (2004) 122] is confirmed, it will
imply a new physics in the leptonic sector
A randomised trial evaluating Bevacizumab as adjuvant therapy following resection of AJCC stage IIB, IIC and III cutaneous melanoma : an update
At present, there are no standard therapies for the adjuvant treatment of malignant melanoma. Patients with primary tumours with a high-Breslow thickness (stages IIB and IIC) or with resected loco-regional nodal disease (stage III) are at high risk of developing metastasis and subsequent disease-related death. Given this, it is important that novel therapies are investigated in the adjuvant melanoma setting. Since angiogenesis is essential for primary tumour growth and the development of metastasis, anti-angiogenic agents are attractive potential therapeutic candidates for clinical trials in the adjuvant setting. Therefore, we initiated a phase II trial in resected high-risk cutaneous melanoma, assessing the efficacy of bevacizumab versus observation.
In the interim safety data analysis, we demonstrate that bevacizumab is a safe therapy in the adjuvant melanoma setting with no apparent increase in the surgical complication rate after either primary tumour resection and/or loco-regional lymphadenectomy
Reversible Mode Switching in Y coupled Terahertz Lasers
Electrically independent terahertz (THz) quantum cascade lasers (QCLs) are
optically coupled in a Y configuration. Dual frequency, electronically
switchable emission is achieved in one QCL using an aperiodic grating, designed
using computer-generated hologram techniques, incorporated directly into the
QCL waveguide by focussed ion beam milling. Multi-moded emission around 2.9 THz
is inhibited, lasing instead occurring at switchable grating-selected
frequencies of 2.88 and 2.92 THz. This photonic control and switching behaviour
is selectively and reversibly transferred to the second, unmodified QCL via
evanescent mode coupling, without the transfer of the inherent grating losses
Y coupled terahertz quantum cascade lasers
Here we demonstrate a Y coupled terahertz (THz) quantum cascade laser (QCL)
system. The two THz QCLs working around 2.85 THz are driven by independent
electrical pulsers. Total peak THz output power of the Y system, with both arms
being driven synchronously, is found to be more than the linear sum of the peak
powers from the individual arms; 10.4 mW compared with 9.6 mW (4.7 mW + 4.9
mW). Furthermore, we demonstrate that the emission spectra of this coupled
system are significantly different to that of either arm alone, or to the
linear combination of their individual spectra.Comment: 9 pages, 3 figure
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