Detection of Other Planetary Systems Using Photometry

Detection of extrasolar short-period planets, particularly if they are in the liquid-water zone, would be one of the most exciting discoveries of our lifetime. A well-planned space mission has the capability of making this discovery using the photometric method. An Earth-sized planet transiting a Sun-like star will cause a decrease in the apparent luminosity of the star by one part in 10,000 with a duration of about 12 hours and a period of about one year. Given a random orientation of orbital plane alignments with the line-of-sight to a star, and assuming our solar system to be typical, one would expect 1 percent of the stars monitored to exhibit planetary transits. A null result would also be significant and indicate that Earth-sized planets are rare. For the mission to be successful one needs a sensor system that can simultaneously monitor many thousands of stars with a photometric precision of one part in 30,000 per hour of integration. Confirmation of a detection will involve detection of a second transit that will yield a period and predict the time for a third and subsequent transits. The technology issues that need to be addressed are twofold: one is for an appropriate optical design; the other is for a detector system with the necessary photometric precision. Two candidates for the detector system are silicon diodes and CCD's

Organism versus mechanism: Losing our grip on the distinction

The distinction between organism and mechanism is often subtle or unclear and yet can prove to be fundamental to our understanding of the world. It has been tempting for many thinkers to seek to ‘understand’ all of reality through the lens of either the one or the other of these concepts rather than by giving both a place. This article sets out to argue that there is a substantial loss of understanding when either of these metaphors is absolutised to explain all causal processes and patterns in reality. Clarifying the distinction between the two may provide one more tool to grasp what is reductionist in many of the perspectives that have come to dominate public life and science today. This contention is tested on the quest for the design of self-replicating systems (i.e. synthetic organisms) in the nanotech industry. It is common that the concepts of organic functioning and mechanism are used imprecisely and in an overlapping way. This is also true of much scientific debate, especially in the fields of biology, micro-biology and nano-science. This imprecise use signals a reductionist tendency both in the way that the organic is perceived and in terms of the distinctive nature of mechanisms

Modulation of the inflammatory response in hibernation and calorie restriction:lessons for sepsis from metabolic extremes

Sepsis is a life-threatening condition caused by a dysregulated immune response to an infection, resulting in mitochondrial failure and organ dysfunction. Here, I explored the role of hydrogen sulfide (H2S) in preventing organ injury from sepsis by regulation of inflammation and mitochondrial function. The protective properties of H2S were established in hibernation, a physiological model characterized by extreme changes in metabolic rate, while avoiding oxidative organ injury. I showed increased flux through the transsulfuration pathway in hibernating Syrian hamsters, promoting H2S release during arousal (the metabolic active phase of hibernation). Additionally, neutrophil activation was suppressed during arousal, avoiding oxidative stress by immune activation and preventing a downward spiral into organ failure. In adult mice, I showed that administration of H2S as well as boosting endogenous H2S-production by calorie restriction, lowered the pro-inflammatory response during sepsis and protected against kidney damage. Moreover, a higher level of intracellular H2S in neutrophils was associated with improved functionality. Unexpectedly, calorie restriction in progeroid mice exaggerated the (neuro)inflammatory response to sepsis. Collectively, in this thesis I reveal the potential of H2S to modulate mitochondrial and neutrophil function, which may have relevance as a therapeutic target to prevent organ injury in sepsis. Yet, despite promising effects of calorie restriction on sepsis outcome in adult mice, a similar approach had detrimental effects in progeroid mice. Unravelling the pleiotropic effects of calorie restriction and H2S on regulation of immunity and mitochondria might lead to novel therapeutic targets to avoid organ failure in sepsis

T cells in healthy ageing and age-associated vasculitides:exploring their phenotype, function and regulation

Upon ageing, changes in the immune system occur. Ageing of the immune system and of T cells in particular are believed to contribute to age-associated vasculitides. Vasculitides are characterized by inflammation of blood vessels. Giant cell arteritis (GCA) is a form of vasculitis which often overlaps with polymyalgia rheumatica (PMR). Both diseases are ageing-related. GCA and PMR patients have inflammation of larger arteries and (peri) articular structures, respectively. Patients often require long-term treatment with glucocorticoids, which have serious side effects. To obtain a better understanding of the pathogenesis of both diseases and to find new clues for treatment, this thesis aimed to explore changes in T-cell phenotype, function and regulation during ageing and in GCA and PMR.The first results described in this thesis show that immune checkpoints, crucial in activating and controlling T-cell responses, are affected by both age and sex. Differences in T-cell regulation can have consequences for the development of vaccines and for optimisation of immune therapy in which immune checkpoints are targeted.Furthermore, T cells appeared to be important in the pathogenesis of GCA and PMR as they were present at the site of inflammation in both diseases. CD8+ T cells, a specific subset of T cells, were involved in the pathogenesis of GCA as well. CD8+ T cells were easier to activate after in vitro stimulation and were local producers of pro-inflammatory cytokines. Also, CD8+ T cells in the tissues of GCA patients may skew macrophages to a pro-inflammatory phenotype via the production of GM-CSF

Cassini atmospheric chemistry mapper. Volume 1. Investigation and technical plan

The Cassini Atmospheric Chemistry Mapper (ACM) enables a broad range of atmospheric science investigations for Saturn and Titan by providing high spectral and spatial resolution mapping and occultation capabilities at 3 and 5 microns. ACM can directly address the major atmospheric science objectives for Saturn and for Titan, as defined by the Announcement of Opportunity, with pivotal diagnostic measurements not accessible to any other proposed Cassini instrument. ACM determines mixing ratios for atmospheric molecules from spectral line profiles for an important and extensive volume of the atmosphere of Saturn (and Jupiter). Spatial and vertical profiles of disequilibrium species abundances define Saturn's deep atmosphere, its chemistry, and its vertical transport phenomena. ACM spectral maps provide a unique means to interpret atmospheric conditions in the deep (approximately 1000 bar) atmosphere of Saturn. Deep chemistry and vertical transport is inferred from the vertical and horizontal distribution of a series of disequilibrium species. Solar occultations provide a method to bridge the altitude range in Saturn's (and Titan's) atmosphere that is not accessible to radio science, thermal infrared, and UV spectroscopy with temperature measurements to plus or minus 2K from the analysis of molecular line ratios and to attain an high sensitivity for low-abundance chemical species in the very large column densities that may be achieved during occultations for Saturn. For Titan, ACM solar occultations yield very well resolved (1/6 scale height) vertical mixing ratios column abundances for atmospheric molecular constituents. Occultations also provide for detecting abundant species very high in the upper atmosphere, while at greater depths, detecting the isotopes of C and O, constraining the production mechanisms, and/or sources for the above species. ACM measures the vertical and horizontal distribution of aerosols via their opacity at 3 microns and, particularly, at 5 microns. ACM recovers spatially-resolved atmospheric temperatures in Titan's troposphere via 3- and 5-microns spectral transitions. Together, the mixing ratio profiles and the aerosol distributions are utilized to investigate the photochemistry of the stratosphere and consequent formation processes for aerosols. Finally, ring opacities, observed during solar occultations and in reflected sunlight, provide a measurement of the particle size and distribution of ring material. ACM will be the first high spectral resolution mapping spectrometer on an outer planet mission for atmospheric studies while retaining a high resolution spatial mapping capability. ACM, thus, opens an entirely new range of orbital scientific studies of the origin, physio-chemical evolution and structure of the Saturn and Titan atmospheres. ACM provides high angular resolution spectral maps, viewing nadir and near-limb thermal radiation and reflected sunlight; sounds planetary limbs, spatially resolving vertical profiles to several atmospheric scale heights; and measures solar occultations, mapping both atmospheres and rings. ACM's high spectral and spatial resolution mapping capability is achieved with a simplified Fourier Transform spectrometer with a no-moving parts, physically compact design. ACM's simplicity guarantees an inherent stability essential for reliable performance throughout the lengthy Cassini Orbiter mission