Techniques and Technologies for Earth-twin Discoveries

In this Thesis I present and discuss the work completed during my three and a half years as a PhD student in the Exoplanet Research Group of the Cavendish Laboratory, University of Cambridge, UK. Most of my work has been in collaboration and partnership with the HARPS3 instrument and the Terra Hunting Experiment. My focus is on the development of new techniques and technologies that are aimed at aiding the discovery of an ‘Earth-twin’ exoplanet. In the context of this work, I use the term Earth-twin to mean an Earth-massed rocky planet orbiting a Sun-like star at a period of around 300 days. I created a pipeline prototype for fitting planetary models to radial velocity (RV) data. The data can contain any number of random or systematic noise sources, and can be poorly sampled. The analysis is conducted in a nested-sampling Bayesian framework and thus allows for the direct statistical comparison of different planetary models given some data set, and produces full posterior estimation for all the parameters of all the models. I used this analysis technique to test the feasibility of using intense ground-based RV surveys to detect Earth-twins, and to compare the results with typical survey cadences. I found that an intense survey reliably and regularly finds a variety of planets, including the Earth-twins, and out-performs the typical survey cadence. The major new technology I have developed is an experiment to measure the geometric positions of the pixels of an optical CCD, and the data analysis pipeline to compute the results. In exoplanet science, precise measurements of the Doppler shift of the stellar spectral lines enable us to confirm the presence of planets. However, at some level of precision, our uncertainty of the detector itself starts to inhibit our detection capability. Hence, if we are to be successful in the discovery of low mass planets, we require knowledge of the sub-pixel structure of our detector. I used the analysis scripts to help plan and design an optical experiment which was then built to analyse a large format optical detector and measure the positions of the pixels. I found the simulation of the experiment can measure the pixel positions to a precision of less than 0.001 pixels, but the experiment was plagued with thermal variations and ultimately was not capable of such precise measurements.STF

A New Soil Conservation Methodology and Application to Cropping Systems in Tropical Steeplands: A comparative synthesis of results obtained in ACIAR Project PN 9201

Land Economics/Use,

Middle Atmosphere Program. Handbook for MAP. Volume 13: Ground-based Techniques

Topics of activities in the middle Atmosphere program covered include: lidar systems of aerosol studies; mesosphere temperature; upper atmosphere temperatures and winds; D region electron densities; nitrogen oxides; atmospheric composition and structure; and optical sounding of ozone

Detecting cosmological reionization on large scales through the 21 cm HI line

This thesis presents the development of new techniques for measuring the mean redshifted 21 cm line of neutral hydrogen during reionization. This is called the 21 cm cosmological reionization monopole. Successful observations could identify the nature of the first stars and test theories of galaxy and large-scale structure formation. The goal was to specify, construct and calibrate a portable radio telescope to measure the 21 cm monopole in the frequency range 114 MHz to 228 MHz, which corresponds to the redshift range 11.5 > z > 5.2. The chosen approach combined a frequency independent antenna with a digital correlation spectrometer to form a correlation radiometer. The system was calibrated against injected noise and against a modelled galactic foreground. Components were specified for calibration of the sky spectrum to 1 mK/MHz relative accuracy. Comparing simulated and measured spectra showed that bandpass calibration is limited to 11 K, that is 1% of the foreground emission, due to larger than expected frequency dependence of the antenna pattern. Overall calibration, including additive contributions from the system and the radio foreground, is limited to 60 K. This is 160 times larger than the maximum possible monopole amplitude at redshift eight. Future work will refine and extend the system known as the Cosmological Reionization Experiment Mark I (CoRE Mk I)

The Dipole Response of an Ionization Threshold within Ultrashort and Strong Fields

In this work, the strong-field-modified dipole response at the ionization threshold of helium is studied. The dipole response is induced by an attosecond pulse in the extreme ultraviolet spectral range and is manipulated by an ultrashort and strong femtosecond pulse in the near-infrared. To probe the response, the transient absorption spectrum of helium is recorded for different time delays between both pulses and different intensities of the femtosecond pulse. From the spectra, the dipole response of the ionization threshold is reconstructed, which is linked to the dynamics of excited electrons with energies in the transition region from bound to free. To identify the underlying processes of light-matter interaction leading to the observed structures in the time and spectral domain, different quantum-mechanical model simulations are conducted. As a result, the measured dipole response reveals light-induced energy shifts of the photoelectron’s kinetic energy close to the parent ion, signatures for field-driven recollisions of a photoelectron into the parent ion, and a temporal amplitude and phase gating mechanism. With the latter, the build-up dynamics of complex spectral structures are temporally resolved, which are the time-dependent separation and line-shape modification of the doubly excited Rydberg series as well as the temporal build-up of the ionization threshold

Expanding the Lexicon

The book series is dedicated to the study of the multifaceted dynamics of wordplay as an interface phenomenon. The contributions aim to bring together approaches from various disciplines and present case studies on different communicative settings, including everyday language and literary communication, and thus offer fresh perspectives on wordplay in the context of linguistic innovation, language contact, and speaker-hearer-interaction