Modelling of the ring current in Saturn's magnetosphere

International audienceThe existence of a ring current inside Saturn's magnetosphere was first suggested by Smith et al. (1980) and Ness et al. (1981, 1982), in order to explain various features in the magnetic field observations from the Pioneer 11 and Voyager 1 and 2 spacecraft. Connerney et al. (1983) formalized the equatorial current model, based on previous modelling work of Jupiter's current sheet and estimated its parameters from the two Voyager data sets. Here, we investigate the model further, by reconsidering the data from the two Voyager spacecraft, as well as including the Pioneer 11 flyby data set. First, we obtain, in closed form, an analytic expression for the magnetic field produced by the ring current. We then fit the model to the external field, that is the difference between the observed field and the internal magnetic field, considering all the available data. In general, through our global fit we obtain more accurate parameters, compared to previous models. We point out differences between the model's parameters for the three flybys, and also investigate possible deviations from the axial and planar symmetries assumed in the model. We conclude that an accurate modelling of the Saturnian disk current will require taking into account both of the temporal variations related to the condition of the magnetosphere, as well as non-axisymmetric contributions due to local time effects. Key words. Magnetospheric physics (current systems; planetary magnetospheres; plasma sheet)</b

Prospective study of a molecular selection profile for RAS wild type colorectal cancer patients receiving irinotecan-cetuximab

Background: The aim of our study was to evaluate whether a panel of biomarkers, prospectively analysed might be able to predict patients' clinical outcome more accurately than RAS status alone. Methods: K-RAS (exons 2, 3, 4) wild type colorectal cancer patients, candidates to second/third-line cetuximab with chemotherapy were prospectively allocated into 2 groups on the basis of their profile: favourable (BRAF and PIK3CA exon 20 wild type, EGFR GCN ≥ 2.6, HER-3 Rajkumar score ≤ 8, IGF-1 immunostaining < 2) or unfavourable (any of the previous markers altered or mutated). After the introduction of N-RAS status (exons 2, 3, 4) only RAS wild type patients were considered eligible. Results: Forty-six patients were enrolled. Seventeen patients (37%) were allocated to the favourable and 29 patients (63%) to the unfavourable profile. RR in the favourable and unfavourable group was 11/17 (65%) and 2/29 (7%) (p = 0.007) respectively. The favourable group also showed an improved PFS (8months vs. 3months, p < 0.0001) and OS (15months vs. 6months, p < 0.0001). Conclusions: Our results suggest that prospective selection of optimal candidates for cetuximab treatment is feasible and may be able to improve clinical outcom

Elimination of Clock Jitter Noise in Spaceborn Laser Interferometers

Space gravitational wave detectors employing laser interferometry between free-flying spacecraft differ in many ways from their laboratory counterparts. Among these differences is the fact that, in space, the end-masses will be moving relative to each other. This creates a problem by inducing a Doppler shift between the incoming and outgoing frequencies. The resulting beat frequency is so high that its phase cannot be read to sufficient accuracy when referenced to state-of-the-art space-qualified clocks. This is the problem that is addressed in this paper. We introduce a set of time-domain algorithms in which the effects of clock jitter are exactly canceled. The method employs the two-color laser approach that has been previously proposed, but avoids the singularities that arise in the previous frequency-domain algorithms. In addition, several practical aspects of the laser and clock noise cancellation schemes are addressed.Comment: 20 pages, 5 figure

Prognostic value for incidental antihypertensive therapy with β-blockers in metastatic colorectal cancer

Previous studies suggested that the incidental use of β-blockers might influence clinical outcome in solid tumors. We assessed the correlation between the incidental use of β-blockers and clinical outcome in colorectal cancer patients treated with first-line chemotherapy alone or in combination with bevacizumab in metastatic colorectal cancer patients. We collected data from 235 metastatic colorectal cancer patients treated with first-line chemotherapy alone (128 patients) or with bevacizumab (107 patients). Patients were stratified for clinical factors such as β-blockers use, age, sex, and site of metastases, previous adjuvant chemotherapy and ECOG performance status. In the chemotherapy alone group patients receiving β-blockers showed an improved overall survival (median OS 41.3 vs 25.7 months, P = 0.03, HR: 2.26, 95% CI: 1.05-3.24). A significant relationship with improved response rate was also evident for B-blocker users (P = 0.044). On the contrary in the β-blockers users group treated with chemotherapy in combination with bevacizumab we observed a trend toward a worse overall survival although nonstatistically significant (median OS 18.5 vs 23.6 months, HR: 0. 89, 95% CI: 0.38-2.03, P = 0.77). Our analysis confirmed a potential prognostic role for the use of β-blockers in colorectal cancer patients treated with chemotherapy. Our findings also suggest a potential worse outcome for patients on β-blockers receiving bevacizumab. Future prospective studies should include the incidental use of β-blockers as stratification factor for clinical outcome

A Markov Chain based method for generating long-range dependence

This paper describes a model for generating time series which exhibit the statistical phenomenon known as long-range dependence (LRD). A Markov Modulated Process based upon an infinite Markov chain is described. The work described is motivated by applications in telecommunications where LRD is a known property of time-series measured on the internet. The process can generate a time series exhibiting LRD with known parameters and is particularly suitable for modelling internet traffic since the time series is in terms of ones and zeros which can be interpreted as data packets and inter-packet gaps. The method is extremely simple computationally and analytically and could prove more tractable than other methods described in the literatureComment: 8 pages, 2 figure

Time Delay Predictions in a Modified Gravity Theory

The time delay effect for planets and spacecraft is obtained from a fully relativistic modified gravity theory including a fifth force skew symmetric field by fitting to the Pioneer 10/11 anomalous acceleration data. A possible detection of the predicted time delay corrections to general relativity for the outer planets and future spacecraft missions is considered. The time delay correction to GR predicted by the modified gravity is consistent with the observational limit of the Doppler tracking measurement reported by the Cassini spacecraft on its way to Saturn, and the correction increases to a value that could be measured for a spacecraft approaching Neptune and Pluto.Comment: 5 pages, LaTex file, no figures. Corrections to Table

Mapping the gravitational wave background

The gravitational wave sky is expected to have isolated bright sources superimposed on a diffuse gravitational wave background. The background radiation has two components: a confusion limited background from unresolved astrophysical sources; and a cosmological component formed during the birth of the universe. A map of the gravitational wave background can be made by sweeping a gravitational wave detector across the sky. The detector output is a complicated convolution of the sky luminosity distribution, the detector response function and the scan pattern. Here we study the general de-convolution problem, and show how LIGO (Laser Interferometric Gravitational Observatory) and LISA (Laser Interferometer Space Antenna) can be used to detect anisotropies in the gravitational wave background.Comment: 16 pages, 6 figures. Submitted to CQ

Sensitivity curves for spaceborne gravitational wave interferometers

To determine whether particular sources of gravitational radiation will be detectable by a specific gravitational wave detector, it is necessary to know the sensitivity limits of the instrument. These instrumental sensitivities are often depicted (after averaging over source position and polarization) by graphing the minimal values of the gravitational wave amplitude detectable by the instrument versus the frequency of the gravitational wave. This paper describes in detail how to compute such a sensitivity curve given a set of specifications for a spaceborne laser interferometer gravitational wave observatory. Minor errors in the prior literature are corrected, and the first (mostly) analytic calculation of the gravitational wave transfer function is presented. Example sensitivity curve calculations are presented for the proposed LISA interferometer. We find that previous treatments of LISA have underestimated its sensitivity by a factor of $\sqrt{3}$.Comment: 27 pages + 5 figures, REVTeX, accepted for publication in Phys Rev D; Update reflects referees comments, figure 3 clarified, figure 5 corrected for LISA baselin

Heterodyne laser tracking at high Doppler rates

A design is described for a transmitter/receiver system that may be used in a spaceborne laser heterodyne tracking system to produce a high-precision interferometer. We present a two-color laser scheme that enables accurate phase measurement even in the presence of a large Doppler offset between the incoming and outgoing signals. The beat note between the two lasers provides a built-in frequency reference, while the delay line produced by the travel time of the tracking signal provides a stable self-comparison that measures drift in the frequency reference so that it may be corrected for. The resulting noise in the link is only the residual laser phase jitter and the shot noise in the phase measurement