Sun-as-a-Star Observation of Flares in Lyman {\alpha} by the PROBA2/LYRA radiometer

There are very few reports of flare signatures in the solar irradiance at H i Lyman {\alpha} at 121.5 nm, i.e. the strongest line of the solar spectrum. The LYRA radiometer onboard PROBA2 has observed several flares for which unambiguous signatures have been found in its Lyman-{\alpha} channel. Here we present a brief overview of these observations followed by a detailed study of one of them, the M2 flare that occurred on 8 February 2010. For this flare, the flux in the LYRA Lyman-{\alpha} channel increased by 0.6%, which represents about twice the energy radiated in the GOES soft X-ray channel and is comparable with the energy radiated in the He ii line at 30.4 nm. The Lyman-{\alpha} emission represents only a minor part of the total radiated energy of this flare, for which a white-light continuum was detected. Additionally, we found that the Lyman-{\alpha} flare profile follows the gradual phase but peaks before other wavelengths. This M2 flare was very localized and has a very brief impulsive phase, but more statistics are needed to determine if these factors influence the presence of a Lyman-{\alpha} flare signal strong enough to appear in the solar irradiance.Comment: in press for Solar Physic

A Space-Time Discontinuous Galerkin Trefftz Method for time dependent Maxwell's equations

We consider the discretization of electromagnetic wave propagation problems by a discontinuous Galerkin Method based on Trefftz polynomials. This method fits into an abstract framework for space-time discontinuous Galerkin methods for which we can prove consistency, stability, and energy dissipation without the need to completely specify the approximation spaces in detail. Any method of such a general form results in an implicit time-stepping scheme with some basic stability properties. For the local approximation on each space-time element, we then consider Trefftz polynomials, i.e., the subspace of polynomials that satisfy Maxwell's equations exactly on the respective element. We present an explicit construction of a basis for the local Trefftz spaces in two and three dimensions and summarize some of their basic properties. Using local properties of the Trefftz polynomials, we can establish the well-posedness of the resulting discontinuous Galerkin Trefftz method. Consistency, stability, and energy dissipation then follow immediately from the results about the abstract framework. The method proposed in this paper therefore shares many of the advantages of more standard discontinuous Galerkin methods, while at the same time, it yields a substantial reduction in the number of degrees of freedom and the cost for assembling. These benefits and the spectral convergence of the scheme are demonstrated in numerical tests

Molecular dynamics simulations of the evaporation of particle-laden droplets

We use molecular dynamics simulations to study the evaporation of particle-laden droplets on a heated surface. The droplets are composed of a Lennard-Jones fluid containing rigid particles which are spherical sections of an atomic lattice, and heating is controlled through the temperature of an atomistic substrate. We observe that sufficiently large (but still nano-sized) particle-laden drops exhibit contact line pinning, measure the outward fluid flow field which advects particle to the drop rim, and find that the structure of the resulting aggregate varies with inter-particle interactions. In addition, the profile of the evaporative fluid flux is measured with and without particles present, and is also found to be in qualitative agreement with earlier theory. The compatibility of simple nanoscale calculations and micron-scale experiments indicates that molecular simulation may be used to predict aggregate structure in evaporative growth processes

Separated Oscillatory Fields for High-Precision Penning Trap Mass Spectrometry

Ramsey's method of separated oscillatory fields is applied to the excitation of the cyclotron motion of short-lived ions in a Penning trap to improve the precision of their measured mass. The theoretical description of the extracted ion-cyclotron-resonance line shape is derived out and its correctness demonstrated experimentally by measuring the mass of the short-lived $^{38}$Ca nuclide with an uncertainty of $1.6\cdot 10^{-8}$ using the ISOLTRAP Penning trap mass spectrometer at CERN. The mass value of the superallowed beta-emitter $^{38}$Ca is an important contribution for testing the conserved-vector-current hypothesis of the electroweak interaction. It is shown that the Ramsey method applied to mass measurements yields a statistical uncertainty similar to that obtained by the conventional technique ten times faster.Comment: 5 pages, 4 figures, 0 table

Aggregation and stability in parasite-host models

Journal ArticleThis paper generalizes the two-dimensional approximation of models of macroparasites on homogeneous populations developed by Anderson & May (1978), focusing on how the dispersion (the variance to mean ratio) of the equilibrium distribution of parasites on hosts is related to the stability of the equilibrium. We show in the approximate system that the equilibrium is stabilized not by aggregation, but by dispersion which increases as a function of the mean. Computer simulations indicate, however, that this analysis fails to capture properly the dynamics of the full system, raising the question of whether any two-dimensional system could produce an adequate approximation. We discuss the relevance of our results to several empirical studies which have examined the relation of dispersion to the mean

CSF lactate dehydrogenase activity in patients with Creutzfeldt-Jakob disease exceeds that in other dementias

The diagnosis of Creutzfeldt- Jakob disease (CJD) is still made by exclusion of other dementias. We now evaluated lactate dehydrogenase (LDH) in the cerebrospinal fluid (CSF) as a possible additional diagnostic tool. CSF LDH levels of patients with CJD ( n = 26) were compared with those in other dementias ( n = 28). LDH isoenzymes were determined in a subset ( n = 9). Total LDH and isoenzyme LDH-1 were significantly higher, whereas the fractions of LDH-2 and LDH-3 were significantly lower in CJD patients. We conclude that in addition to established CSF parameters, LDH and its isoenzymes might serve as a further help to discriminate between CJD and other dementias. Copyright (C) 2004 S. Karger AG, Basel

Sun-as-a-star Observation of White-Light Flares

Solar flares radiates energy at all wavelengths, but the spectral distribution of this energy is still poorly known. White-light continuum emission is sometimes observed and the flares are then termed "white-light flares" (WLF). In this paper, we investigate if all flares are white-light flares and how is the radiated energy spectrally distributed. We perform a superposed epoch analysis of spectral and total irradiance measurements obtained since 1996 by the SOHO and GOES spacecrafts at various wavelength, from Soft X-ray to the visible domain. The long-term record of solar irradiance and excellent duty cycle of the measurements allow us to detect a signal in visible irradiance even for moderate (C-class) flares, mainly during the impulsive phase. We identify this signal as continuum emission emitted by white-light flares, and find that it is consistent with a blackbody emission at ~9000K. We estimate for several sets of flares the contribution of the WL continuum and find it to be of ~70% of the total radiated energy. We re-analyse the X17 flare that occurred on 28 October 2003 and find similar results. This paper brings evidence that all flares are white-light flares and that the white-light continuum is the main contributor to the total radiated energy; this continuum is consistent with blackbody spectrum at ~9000K. These observational results are important in order to understand the physical mechanisms during flares and open the way to a possible contribution of flares to TSI variations