Use of integrated optical waveguide probes as an alternative to fiber probes for sensing of light backscattered from small volumes

We show that for light collection from thin samples, integrated probes can present a higher efficiency than conventional fiber probes, despite having a smaller collection area. Simulation results are validated by experiments

Pulsations detected in the line profile variations of red giants: Modelling of line moments, line bisector and line shape

Contents: So far, red giant oscillations have been studied from radial velocity and/or light curve variations, which reveal frequencies of the oscillation modes. To characterise radial and non-radial oscillations, line profile variations are a valuable diagnostic. Here we present for the first time a line profile analysis of pulsating red giants, taking into account the small line profile variations and the predicted short damping and re-excitation times. We do so by modelling the time variations in the cross correlation profiles in terms of oscillation theory. Aims: The performance of existing diagnostics for mode identification is investigated for known oscillating giants which have very small line profile variations. We modify these diagnostics, perform simulations, and characterise the radial and non-radial modes detected in the cross correlation profiles. Methods: Moments and line bisectors are computed and analysed for four giants. The robustness of the discriminant of the moments against small oscillations with finite lifetimes is investigated. In addition, line profiles are simulated with short damping and re-excitation times and their line shapes are compared with the observations. Results: For three stars, we find evidence for the presence of non-radial pulsation modes, while for $\xi$ Hydrae perhaps only radial modes are present. Furthermore the line bisectors are not able to distinguish between different pulsation modes and are an insufficient diagnostic to discriminate small line profile variations due to oscillations from exoplanet motion.Comment: 12 pages, 10 figures, accepted by A&

Arrayed-waveguide-grating light collector for on-chip spectroscopy

We present a novel arrayed-waveguide-grating (AWG) device with improved external (biomedical) signal collection for use in on-chip spectroscopy. The collection efficiency of the device is compared to that of a standard AWG. We also present experimental results on the collection efficiency and size of the collection volume

Characteristics of solar-like oscillations in red giants observed in the CoRoT exoplanet field

Observations during the first long run (~150 days) in the exo-planet field of CoRoT increase the number of G-K giant stars for which solar-like oscillations are observed by a factor of 100. This opens the possibility to study the characteristics of their oscillations in a statistical sense. We aim to understand the statistical distribution of the frequencies of maximum oscillation power (nu_max) in red giants and to search for a possible correlation between nu_max and the large separation (delta_nu). The nu_max distribution shows a pronounced peak between 20 - 40 microHz. For about half of the stars we obtain delta_nu with at least two methods. The correlation between nu_max and delta_nu follows the same scaling relation as inferred for solar-like stars. The shape of the nu_max distribution can partly be explained by granulation at low frequencies and by white noise at high frequencies, but the population density of the observed stars turns out to be also an important factor. From the fact that the correlation between delta_nu and nu_max for red giants follows the same scaling relation as obtained for sun-like stars, we conclude that the sound travel time over the pressure scale height of the atmosphere scales with the sound travel time through the whole star irrespective of evolution.Comment: Accepted for publication in Astronomy and Astrophysics (CoRoT special issue), 5 pages, 7 figures and 1 tabl

Identification of the accretion rate for annually resolved archives

International audienceThe past environment is often reconstructed by measuring a given proxy (e.g. ?18O) in an environmental archive, i.e. a species which gradually accumulates mass and records the current environment during this mass formation (e.g. corals, shells, trees, etc...). When such an environmental proxy is measured, its values are known as a function of distance. However, to relate the data to environmental variations, the date associated with each measurement, i.e. the time base, should be known. This is not straightforward solved, since species usually do not grow at constant rates. In this paper, we investigate this problem for annually resolved archives, which exhibit a certain periodicity. Such signals are often found in clams or corals. Due to variations in accretion rate the data along the distance axis have a disturbed periodic profile. A method is developed to extract information about the accretion rate, such that the original (periodic) signal as function of time can be recovered. Simultaneously the exact shape of the periodic signal is estimated. The final methodology is quasi-independent of choices made by the investigator. Every step in the procedure is described in detail and finally, the method is exemplified on a real world example

Identification of the time base in environmental archives

The second chapter handles the measurement. These are often collected with a Laser Ablation Inductively Coupled Mass Spectrometer (LA-ICP-MS) and the first problem we encountered was the calibration of this instrument. It is used to measure trace elements with an incredibly high spatial resolution. Of course, it has also some major disadvantages. One of these is that the laser, which is used to ablate the solid substrate, has a variable intensity. In addition several other internal instrumental parameters seem to vary over time in an unpredictable manner. Therefore, people use internal standards for more than twenty years. Such internal standards are elements whose concentration does not vary over the sample. Consequently,all variation detected in these internal standards must be due to artificial variation in the instrument. Because the drift of the instrument is reflected in the measurementofthe internal standard, all other concentrationscan be calibratedaccordingto this internal standard. This simple idea seems to work quite well. Unfortunately, the calibration algorithm does not take into account measurement noise in the signal of the internal standards. This is exactly the improvement that we made: imagine two internal standards, each consisting of the same drift pattern, and disturbed by a different noise pattern. A better approximation of the true drift pattern can be reached by the arithmetic mean of both internal standards.Hereinthe drift remains and the noise cancels out. This idea is further refined, so that the uncertainty on the internal standards can be taken into account as well, and an a priori and an a posteriori verification of the model used is given. Further, the myth of mass dependent internal standards is ruled out and finally a real world example is processed. An additional important property of the proposed calibration is that an internal quality check is performed, which warns the investigator if some artefacts or problems occurred during the measurement. The remaining part of this work is devoted to the reconstruction of time series. One of the major problems with data-processing of proxy records (e.g. stable isotope ratios of oxygen or carbon, or trace elements in shells, sponges, corals, sediment cores, etc ) is the dating of individual observations. All these proxy records are measured as function of a distance, while generally the time series are desired. Due to variations and differences in accretion rate, each record has its unique distance series, which cannot be compared with other records or models. Therefore, distance series are transformed into time series. However, this is only possible if additional information about the accretion rate is available. Unfortunately, this is mostly not the case and thus additional assumptions are necessary. Such assumption can be made about the signal and formally written down in the signal model. In addition,the concept of a time base distortion is introduced.As will be shown,this enables us to estimate variations in accretion rate. For this, we started from a previously estimated time base (if this is unknown, we initialize the time base assuming a constant accretion rate). Next, we allow this base to be distorted due to nonlinear accretion rates or hiatuses and we will show how such a distortion can be estimated. In the third chapter, we have illustrated how the time series can be reconstructed, assuming a periodic proxy-record. Therefore, the concept of time base distortions is introduced. First, we propose a model for variations in accretion rate. Next, we illustrate how this accretion rate can be identified and estimated in the Fourier spectrum of the proxy. This approach is compared with the widely used anchor point method in two manners: the assumptions made are compared and next the sensitivity of both methods w.r.t. stochastic noise is illustrated on a simulation. Three case studies are incorporated to validate the method and to illustrate its use

Introductory clifford analysis

In this chapter an introduction is given to Clifford analysis and the underlying Clifford algebras. The functions under consideration are defined on Euclidean space and take values in the universal real or complex Clifford algebra, the structure and properties of which are also recalled in detail. The function theory is centered around the notion of a monogenic function, which is a null solution of a generalized Cauchy–Riemann operator, which is rotation invariant and factorizes the Laplace operator. In this way, Clifford analysis may be considered as both a generalization to higher dimension of the theory of holomorphic functions in the complex plane and a refinement of classical harmonic analysis. A notion of monogenicity may also be associated with the vectorial part of the Cauchy–Riemann operator, which is called the Dirac operator; some attention is paid to the intimate relation between both notions. Since a product of monogenic functions is, in general, no longer monogenic, it is crucial to possess some tools for generating monogenic functions: such tools are provided by Fueter’s theorem on one hand and the Cauchy–Kovalevskaya extension theorem on the other hand. A corner stone in this function theory is the Cauchy integral formula for representation of a monogenic function in the interior of its domain of monogenicity. Starting from this representation formula and related integral formulae, it is possible to consider integral transforms such as Cauchy, Hilbert, and Radon transforms, which are important both within the theoretical framework and in view of possible applications