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We discover that the scaling property of the cosmology is synonymous with the scalar fields tracing out a particular class of geodesics in moduli space - those which are constructed as integral curves of the gradient of the log of the potential. Given a generic scalar potential we explicitly construct a moduli metric that allows scaling solutions, and we show the converse - how one can construct a potential that allows scaling once the moduli metric is known. We also ask what the origin of such cosmological scalars might be, and look to the scalars in the Kaluza-Klein compactification of higher-dimensional theories for a possible answer. Conventionally these scalars, or moduli fields, are required to be stabilised so that the gauge sector can be used to describe the field content of the standard model. Here we instead take the view that the scalar fields are dynamical moduli describing the squashings of an internal compactified manifold, and study the dynamics of such systems. We additionally consider the cosmological role of the scalar fields generated by the compactification of 11D Einstein gravity on a 7D elliptic twisted torus, which has the attractive features of giving rise to a positive semi-definite potential, and partially fixing the moduli. This compactification is therefore relevant for low energy M-theory, 11D supergravity. We find that there is no slow-roll inflation within a subclass of these twisted tori and give evidence that this result extends to a more general situation. Despite the lack of slow-roll, we find that there is a novel scaling solution in Friedmann cosmologies in which the massive moduli oscillate but maintain a constant energy density relative to the background barotropic fluid.

No description available.

No description available.

This thesis presents a study of early type, emission line objects on small angular scales. Spectroastrometry is used to separate the spectra of unresolved Herbig Ae/Be binary systems. The separated spectra allow the mass ratio of the systems to be established. The separation and mass ratio distribution of the systems suggest that they form via disk fragmentation. To test this conclusion, disk and binary position angles are compared to a model in which the circumstellar disk and binary orbits are co-planar. The data are consistent with the coplanar model and thus with the scenario of disk fragmentation. A search for optical outflows associated with Herbig Ae/Be stars is conducted using integral field unit spectroscopy. No outflows are detected. Therefore, the data cannot constrain the location of the proposed transition from collimated to un-collimated outflows, if such a transition exists. Spectroastrometry is used to probe the origin of the Brackett line emission in the data with sub-milli-arcsecond precision. To explore the potential of spectroastrometry to detect circumstellar disks, spectroastrometric observations of Be stars are presented. It is shown that spectroastrometric data with an angular precision of 0.1 milli-arcseconds can detect milli-arcsecond sized disks. Comparing the spectroastrometric signatures to models of disks with different kinematics demonstrates that Be star disks rotate in a Keplerian fashion, which constrains their formation mechanism. Finally, spectroastrometry over CO bandhead emission is employed to search for disks around massive young stellar objects. Fitting the observed overtone profiles with a model of a circumstellar disk allows the spatial distribution of the CO to be predicted. No signatures of disks are detected. This is entirely consistent with the best fitting models of the emission, and thus with the presence of small-scale disks around massive young stellar objects.

The aims of this research programme were twofold: to analyse the iron isotope compositions of metal grains from ordinary chondrite meteorites over a range of class and petrographic type to investigate redox reactions and thermal metamorphism during primitive planetesimal formation; and to analyse the iron isotope composition of secondary carbonate minerals in Martian meteorite ALH84001 to determine the formation temperature and thus constrain near surface conditions on early Mars. To analyse the iron isotope compositions of these materials it was necessary to develop a methodology using a Nu Plasma multi collector inductively coupled plasma mass spectrometer and a new technique for analysing natural iron-bearing samples without first purifying them by anion exchange chromatography. The purification process can cause fractionation within the sample which may mask small natural fractionation variations. The new methodology developed here yielded reproducible iron isotope ratios to within o.osroo (20) ensuring that small isotopic variations of (i56Fe -0.06roo to 0.3sroo were resolved during the analysis of the ordinary chondrite metal grains. The method for analysing samples containing matrix elements was successful and achieved an accuracy and precision comparable to pure analyte solutions for the analysis of the Martian carbonates. The analysis of the metal grains revealed a correlation between their iron isotope compositions and the redox and thermal metamorphism that these materials have experienced. The results indicate that the degree of iron isotope fractionation can be related to thermal metamorphism temperatures, except for metal grains from type 3 chondrites. This was interpreted as resulting from the type 3 chondrites not getting hot enough during thermal metamorphism to overprint the original igneous isotopic signatures. The a-rich carbonates in ALH84001 were petrographically characterised to place them within the known carbonate assemblage sequence which implied that the zoned carbonate deposition occurred during multiple phases. The zoned carbonates were then analysed for iron isotope composition and an isotopic fractionation variation for (i56Fe of -0.6%0 was determined relative to bulk Martian silicates. This indicated a formation temperature of approximately ±800( (20) and implied that liquid water was stable on or near the surface during this time.

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The integration of 300 mK semiconductor bolometers and 4 K hot-electron bolometers with commercial pulse tube cryocooler (PTC) systems has been investigated. The process also involved the integration of a two-stage 4He-3He adsorption refrigerator with the PTC to produce a cryogen free sub-Kelvin system. Thermometry electronics with an onboard computer and an internet interface have been developed that allow for remote and/or automatic operation. Methods to reduce excess noise seen in the 300 mK bolometer have been investigated to demonstrate the possibility of using high sensitivity bolometric detectors in this system for astrophysics and Earth observation instruments. In order to minimise the microphonic induced noise and thermal fluctuations from the pulse tube operation an AC biasing circuit was used. The origin of excess noise components in the bolometer readout have been identified and quantified as a function of both mechanical and electrical configurations of the cold components. With the optimum configuration thermal fluctuation noise, rather than microphonic induced noise dominates, reducing the bolometer sensitivity by approximately two times compared to the same device operated in a liquid helium cooled cryostat. Clearly the performance could be improved by increasing the thermal isolation of the sorption refrigerator from the pulse tube temperature oscillations. The hot-electron bolometer behaved nominally up to 6 kHz when operated in the cryogen free cryostat. Dynamic audio frequency noise deteriorated the detector's performance above 6 kHz and has been attributed to the movement of the helium gas through the PTC's valves and orifices during its thermodynamic cycle. Restrictions of the signal analyser mean that it is unclear whether this microphonic noise is present above 1 MHz.

The galactic disk is largely composed of hot, rarefied gas also called the inter cloud medium (ICM). The cooler regions of the ICM are dominated by molecular species and dust. Immersed in this neutral medium are dense agglomerations of primarily H2, called giant molecular clouds (GMCs). The GMCs have a velocity dispersion of order a few km s_1, superimposed on their orbital motion. A GMC, over a single period of rotation of the galaxy, may undergo a few tens of collisions. In the present work, we investigate this rather violent phenomenon and examine the prospects of star formation in the post collision composite gas body. The star formation code, DRAGON, employed for the present work is ill equipped to study the effects of cloud collision on the chemical composition of the ICM. We draw a distinction between the regime of high velocity (precollision Mach numbers in excess of ten) and low velocity (precollision Mach numbers of order unity) cloud collisions, on the basis of the evolution of the gas slab produced in either cases. While the former leads to the formation of a dense shock compressed gas slab, the latter results in a dense pressure compressed gas slab. We observe that strong internal shear in a shock compressed slab suppresses gravitational instability in it. In particular, we observe evidence for the non-linear thin shell instability (NTSI) in the shocked slab formed in a head-on cloud collision. The slab thus dissipates thermal energy and upon the loss of thermal support, collapses to form a thin, long filament along the collision axis. Star formation proceeds in this filament. There is however, no evidence of the NTSI in the oblique shocked slab resulting from off centre cloud collisions, although it is dominated by internal shearing motion. On the other hand, the pressure compressed slab is dominated by gravitational instability and fragments, when the fastest growing mode dominates. The slab develops a number of floccules, which merge to form larger clumps and filamentary structures. The densest regions in these large scale structures then collapse gravitationally. We suggest this as a possible mechanism for the formation of star clusters. YSOs forming in filamentary structures are fed with material streaming along the axis of respective filaments. This material also transfers angular momentum to the accreting protostellar core and the attendant accretion disk is orthogonal to the angular momentum vector of this inflowing material. In the filaments resulting from the collapse of the post-collision shocked slab in a head-on cloud collision, we observe that the accretion disks circumscribing the sinks, are orthogonal to the filament. However, the gas slab resulting from a low velocity, off centre cloud collision is wrapped around by angular momentum and gravitationally fragments to form filaments. This slab tumbles in the plane of the collision (and therefore the axis about which it tumbles, comes out of this plane), the filaments in the slab also tumble with it. In the process they become offset relative to each other and feed angular momentum to the candidate protostellar core along the direction normal to the angular momentum axis. Thus, any attendant accretion disk is expected to be parallel to the filament (also the angular momentum) axis (Whitworth et al., 1995). To test this hypothesis, we collated data for YSOs located in filamentary star forming regions, and outflows originating from them. The scope of our work was limited and restricted to only five filamentary star forming regions in the local universe. Outflows from YSOs generally have small opening angles and are approximately normal to the circumstellar disk. Under this premise, we can get an idea of the orientation of the circumstellar disks relative to their natal filaments. We concluded that 72% outflows were distributed within 45 of being orthogonal to their natal filaments and 28% were distributed within 45 of being parallel to their natal filaments. It is difficult to make a strong claim simply on the basis of this work, which therefore needs to be extended. None the same, it tends to support the mechanism elucidated by Whitworth et al. (1995).

Kinetic Inductance Detectors (KIDs) provide a promising solution to the problem of producing large format arrays of ultra sensitive detectors for astronomy. Traditionally KIDs have been constructed from superconducting quarter-wavelength or half- wavelength resonator elements capacitively coupled to a coplanar feed line. Photons are detected by measuring the change in quasi-particle density caused by the splitting of Cooper pairs in the superconducting resonant element. This change in quasi-particle density alters the kinetic inductance, and hence the resonant frequency of the resonant element. This arrangement requires the quasi-particles generated by photon absorption to be concentrated at positions of high current density in the resonator. This is usually achieved through antenna coupling or quasi-particle trapping. For these detectors to work at wavelengths shorter than around 500 /zra where antenna coupling can introduce a significant loss of efficiency, a direct absorption method needs to be considered. One solution to this problem is the Lumped Element KID (LEKID), which shows no current variation along its length and can be arranged into a photon absorbing area coupled to free space and therefore requiring no antennas or quasi-particle trapping. The work throughout this thesis studies the properties of the LEKID device though simulation and experimental data and lays the foundation for developing an optimised detector using this direct absorption approach.