The EPIC focal plane imaging spectrometers on XMM-Newton use CCDs to record the images and spectra of celestial X-ray sources focused by the three X-ray mirrors. There is one camera at the focus of each mirror; two of the cameras contain seven MOS CCDs, while the third uses twelve PN CCDs, dening a circular eld of view of 30 0 diameter in each case. The CCDs were specially developed for EPIC, and combine high quality imaging with spectral resolution close to the Fano limit. A lter wheel carrying three kinds of X-ray transparent light blocking lter, a fully closed, and a fully open position, is tted to each EPIC instrument. The CCDs are cooled passively and are under full closed loop thermal control. A radio-active source is tted for internal calibration. Data are processed on-board to save telemetry by removing cosmic ray tracks, and generating X-ray event les; a variety of dierent instrument modes are available to increase the dynamic range of the instrument and to enable fast timing. The instruments were calibrated using laboratory X-ray beams, and synchrotron generated monochromatic X-ray beams before launch; in-orbit calibration makes use of a variety of celestial X-ray targets. The current calibration is better than 10% over the entire energy range of 0.2 to 10 keV. All three instruments survived launch and are performing nominally in orbit. In particular full eld-of-view coverage is available, all electronic modes work, and the energy resolution is close to pre-launch values. Radiation damage is well within pre-launch predictions and does not yet impact on the energy resolution. The scientic results from EPIC amply full pre-launch expectations.
We estimate the fluxes of heat and antineutrinos due to primordial radioactivity within the moon. We use a radial density profile, specifying an inner core and a model-averaged crust. Thickness, density, and elevation of the lunar crust are from remote measurements of the gravitational field. Lateral and vertical variations of thorium, uranium, and potassium abundances in the crust follow from a prediction of the lunar bulk chemical composition. We constrain the total contents of thorium, uranium, and potassium using estimates for the earth's primitive mantle. These contents produce $311\pm37$ GW of radiogenic heating and a surface-averaged heat flux of $8.19\pm0.97$ mW/m$^2$. Our lunar model estimates an antineutrino flux of $(1.83\pm0.32)\times10^6$ cm$^{-2}$s$^{-1}$ and an antineutrino inverse beta decay rate of $5.8\pm1.0$ per $10^{32}$ free proton targets per year, both averaged over the surface.
Analyzing paradoxes is interesting and instructive. Sometimes the analysis leads to non-trivial results. This methodological note sets out a paradox arising in the theory of propagation of electromagnetic waves in moving plasmas. The paradox is interesting in itself, and, generally speaking, it should be taken into account when analyzing geoelectromagnetic waves. The paradox is as follows: contrary to expectations, the group velocity of the waves is the same in the comoving and laboratory frames of reference. The condition for the appearance of the paradox is the quadratic dependence of the frequency on the wave number. A paradoxical property manifests itself in the theory of the propagation of radio waves (in particular, whistling atmospherics), Langmuir waves and Alfvén waves. From a cognitive point of view, it is interesting that the paradox can be traced in relation to de Broglie waves. An explanation of the paradox is proposed. Keywords: group velocity, moving plasma, Doppler Effect, dispersion, longitudinal waves, transverse waves.
Parameter values for seismic processing steps are often chosen on a regular grid of samples and interpolated. Active learning instead attempts to optimally select the samples on which parameter values are chosen. For parameters that do not vary smoothly, this often reduces the number of samples that need to be labelled in order to achieve a desired accuracy on the whole dataset. In regression tasks this is typically achieved using a query by committee strategy that selects the samples on which a committee of models is most uncertain. I implement such a strategy for the first break picking task, where the parameters to be chosen are the centre and width of the picking window for each trace. For the committee members I use the centre of the picking window and three popular picking algorithms. Applying this to a real dataset, and with samples corresponding to shot gathers, the active learning approach primarily selects gathers near a jump in the first breaks, and achieves similar levels of accuracy on the whole dataset with about half the number samples picked as when the samples are randomly selected.
Spectrophotometric procedures allow rapid and precise measurements of the pH of natural waters. However, impurities in the acid–base indicators used in these analyses can significantly affect measurement accuracy. This work describes HPLC procedures for purifying one such indicator, meta-cresol purple (mCP), and reports mCP physical–chemical characteristics (thermodynamic equilibrium constants and visible-light absorbances) over a range of temperature (T) and salinity (S). Using pure mCP, seawater pH on the total hydrogen ion concentration scale (pHT) can be expressed in terms of measured mCP absorbance ratios (R = λ2A/λ1A) as follows:where −log(K2Te2) = a + (b/T) + c ln T – dT; a = −246.64209 + 0.315971S + 2.8855 × 10–4S2; b = 7229.23864 – 7.098137S – 0.057034S2; c = 44.493382 – 0.052711S; d = 0.0781344; and mCP molar absorbance ratios (ei) are expressed as e1 = −0.007762 + 4.5174 × 10–5T and e3/e2 = −0.020813 + 2.60262 × 10–4T + 1.0436 × 10–4 (S – 35). The mCP absorbances, λ1A and λ2A, used to calculate R are measured at wavelengths (λ) of 434 and 578 nm. This characterization is appropriate for 278.15 ≤ T ≤ 308.15 and 20 ≤ S ≤ 40.
The full Stokes equations are solved by a finite element method for simulation of large ice sheets and glaciers. The simulation is particularly sensitive to the discretization of the grounding line which separates the ice resting on the bedrock and the ice floating on water and is moving in time. The boundary conditions at the ice base are enforced by Nitsche's method and a subgrid treatment of the elements in the discretization close to the grounding line. Simulations with the method in two dimensions for an advancing and a retreating grounding line illustrate the performance of the method. It is implemented in the two dimensional version of the open source code Elmer/ICE.
We present an algorithm that is well suited to find the linear layout of the multiple flow-direction network (directed acyclic graph) for an efficient implicit computation of the erosion term in landscape evolution models. The time complexity of the algorithm varies linearly with the number of nodes in the domain, making it very efficient. The resulting numerical scheme allows us to achieve accurate steady-state solutions in conditions of high erosion rates leading to heavily dissected landscapes. We also establish that contrary to single flow-direction methods such as D8, D$\infty$ multiple flow-direction method follows the theoretical prediction of the linear stability analysis and correctly captures the transition from smooth to the channelized regimes. We finally show that the obtained numerical solutions follow the theoretical temporal variation of mean elevation.