A temperature independent driver for Mach-Zehnder modulators

This paper describes a fully differential inductorlesstemperature independent laser driver for a Mach-Zehndermodulator (MZM). The laser driver in this work exhibits robustnessin bandwidth and gain across the temperature range27oC to 135oC. This driver (fabricated using a 130nm CMOSprocess) can achieve a differential output voltage swing of up to4Vpp when driving a 50 Ohm Load at speeds of up to 12.5Gb/sacross a temperature range 27oC to 135oC

Plio-Pleistocene reconstruction of East African and Arabian Sea palaeoclimate

Superimposed upon a long-term trend of aridification, the climate history of Africa was punctuated by episodes of extreme climate variability, characterised by the precessionally-forced appearance and disappearance of large lake systems within the East African Rift Valley. In order to investigate the nature of low-latitude climate variability during the Late Pliocene and Early Pleistocene, this thesis combines high-resolution analyses from one of the lake phases in the Central Kenyan Rift with the reconstruction of long-term changes in the transport of wind-borne terrigenous dust to the Arabian Sea. Climate in both regions is strongly influenced by relative changes in the strength of the Indian Ocean monsoons, which determine rainfall distribution in equatorial East Africa and generate the low-level winds which transport dust offshore from the Arabian Peninsula. In the Baringo-Bogoria basin in the Central Kenyan Rift, a well-dated package of fluvio-lacustrine sediments and diatomite units documents a major humid phase between 2.7 and 2.55 million years ago (Ma), coincident with the intensification of glaciation in the Northern Hemisphere. Stable oxygen isotope measurements of diatom silica, combined with the XRF analysis of whole-sample geochemistry, reveal that the deep lake phase was characterised by wet-dry cycles lasting, on average, 1,400 years. Over longer timescales, variations in the aeolian delivery of lithogenic matter to the Arabian Sea, reflected in normalised flux of titanium, show that monsoonal circulation prior to 2.6 Ma was highly variable and primarily driven by orbitally-forced changes in tropical summer insolation, modulated by the 400,000 year cycle of orbital eccentricity. Millennial-scale fluctuations in the dust record also support the evidence of abrupt wet-dry cycles in East Africa. Such high-resolution cycles are rarely found in older records, thus giving a valuable insight to the nature of short-term fluctuations in Plio-Pleistocene climate

Absorbate-Induced Piezochromism in a Porous Molecular Crystal

Atmospherically stable porous frameworks and materials are interesting for heterogeneous solid–gas applications. One motivation is the direct and selective uptake of pollutant/hazardous gases, where the material produces a measurable response in the presence of the analyte. In this report, we present a combined experimental and theoretical rationalization for the piezochromic response of a robust and porous molecular crystal built from an extensively fluorinated trispyrazole. The electronic response of the material is directly determined by analyte uptake, which provokes a subtle lattice contraction and an observable bathochromic shift in the optical absorption onset. Selectivity for fluorinated absorbates is demonstrated, and toluene is also found to crystallize within the pore. Furthermore, we demonstrate the application of electronic structure calculations to predict a physicochemical response, providing the foundations for the design of electronically tunable porous solids with the chemical properties required for development of novel gas-uptake media

Three and half million year history of moisture availability of South West Africa: Evidence from ODP site 1085 biomarker records

Ocean Drilling Program Site 1085 provides a continuous marine sediment record off southern South West Africa for at least the last three and half million years. The n-alkane ∂13 C record from this site records changes in past vegetation and provides an indication of the moisture availability of SW Africa during this time period. Very little variation, and no apparent trend, is observed in the n-alkane δ13C record, suggesting stable long-term conditions despite significant changes in East African tectonics and global climate. Slightly higher n-alkane δ13C values occur between 3.5 and 2.7 Ma suggesting slightly drier conditions than today. Between 2.5 and 2.7 Ma there is a shift to more negative n-alkane δ13C values suggesting slightly wetter conditions during a ~ 0.2 Ma episode that coincides with the intensification of Northern Hemisphere Glaciation (iNHG). From 2.5 to 0.4 Ma the n-alkane δ13C values are very consistent, varying by less than ± 0.5‰ and suggesting little or no long-term change in the moisture availability of South West Africa over the last 2.5 million years. This is in contrast to the long-term drying trend observed further north offshore from the Namib Desert and in East Africa. A comparison of the climate history of these regions suggests that Southern Africa may have been an area of long-term stability over the last 3.5 Myrs

The application of Bayesian change point detection in UAV fuel systems

AbstractA significant amount of research has been undertaken in statistics to develop and implement various change point detection techniques for different industrial applications. One of the successful change point detection techniques is Bayesian approach because of its strength to cope with uncertainties in the recorded data. The Bayesian Change Point (BCP) detection technique has the ability to overcome the uncertainty in estimating the number and location of change point due to its probabilistic theory. In this paper we implement the BCP detection technique to a laboratory based fuel rig system to detect the change in the pre-valve pressure signal due to a failure in the valve. The laboratory test-bed represents a Unmanned Aerial Vehicle (UAV) fuel system and its associated electrical power supply, control system and sensing capabilities. It is specifically designed in order to replicate a number of component degradation faults with high accuracy and repeatability so that it can produce benchmark datasets to demonstrate and assess the efficiency of the BCP algorithm. Simulation shows satisfactory results of implementing the proposed BCP approach. However, the computational complexity, and the high sensitivity due to the prior distribution on the number and location of the change points are the main disadvantages of the BCP approac

A 30 Gb/s CMOS driver integrated with silicon photonics MZM

A voltage mode modulator driver is proposed in the TSMC 65nm low power CMOS process. In the electrical testing, the driver itself can achieve a bit rate of 40Gb/s with the single-ended output swing of 1.65V. Unlike equivalent CML modulator drivers, when the proposed driver is integrated with the silicon photonic MZM, it does not require an additional biasing network. The integrated electro-optic transmitter can achieve 30Gb/s with an extinction ratio of 4.05dB, with the power consumption of main driver being 323mW