Fast switching of magnetic fields in a magneto-optic trap

Magneto-optic traps which employ current windings to generate pulsed magnetic fields require rapid switch-off times for many applications. Practical difficulties in attaining rapid switch-off of the magnetic field, including the generation of induced currents, are addressed. Several methods for minimizing the switch-off time are presented which do not require complex feedback mechanisms involving direct measurement of the magnetic field

Feedback control of an atom laser

We report the first real-time feedback control of an atom laser. The unique feature of metastable helium atoms, the production of ions in the atom laser outcoupling process, is exploited to actively control the spatial location inside the Bose-Einstein condensate where outcoupling occurs. Unlike alkali atom lasers, this provides almost instantaneous feedback which reduces frequency, amplitude and spatial mode fluctuations in the atom laser beam

Shotgun proteomics reveals temperature-dependent regulation of major nutrient metabolism in coastal Synechococcus sp. WH5701

Marine cyanobacteria are major contributors to the oceanic carbon sink and are predicted to increase in numbers in the future warmed ocean. As a result, the influence of marine cyanobacteria on marine biogeochemical cycling will likely be enhanced. Associated with elevations in temperature the ocean will undergo increased stratification, reducing supply of essential nutrients to upper phototrophic layers. It is therefore critical that we resolve the manners by which cyanobacteria respond to variations in temperature, and consequences for major nutrient metabolism which may ultimately direct global biogeochemistry and trophic transfer. In this study we use the coastal Synechococcus sp. WH5701 to examine proteomic alterations in major nutrient (C, N and P) metabolic pathways following exposure to varying temperature. In response to temperature treatments, Synechococcus displayed higher rates of growth and photosynthetic efficiency when temperatures were raised from 17 °C, to 23 °C and 28 °C, associated with a significant ∼30–40 % alteration in the cellular proteome. As temperatures increased, proteomic investment towards photosynthetic machinery appeared up-regulated, whilst abundance of RuBisCO was reduced, associated with an apparent alteration in CCM composition and carbon metabolism. N demand appeared to increase in-line with temperature, associated with alterations in the GS-GOGAT pathway, likely due to increased demand for and efficiency of protein synthesis. In contrast, P demand at the highest temperature appeared reduced as investment in the ribosome declines due to improved translation efficiency, whilst luxury P-storage appeared a feature of growth at low temperature. It appears likely that as seawater temperatures rise under ocean warming, the biochemical composition of cyanobacteria will be altered, increasing cellular C- and N- to P ratios, ultimately impacting upon their contribution to oceanic biogeochemical cycling

The cellular response to ocean warming in Emiliania huxleyi

Marine phytoplankton contribute substantially to the global flux of carbon from the atmosphere to the deep ocean. Sea surface temperatures will inevitably increase in line with global climate change, altering the performance of marine phytoplankton. Differing sensitivities of photosynthesis and respiration to temperature, will likely shift the strength of the future oceanic carbon sink. To further clarify the molecular mechanisms driving these alterations in phytoplankton function, shotgun proteomic analysis was carried out on the globally-occurring coccolithophore Emiliania huxleyi exposed to moderate- (23°C) and elevated- (28°C) warming. Compared to the control (17°C), growth of E. huxleyi increased under elevated temperatures, with higher rates recorded under moderate- relative to elevated- warming. Proteomic analysis revealed a significant modification of the E. huxleyi cellular proteome as temperatures increased: at lower temperature, ribosomal proteins and photosynthetic machinery appeared abundant, as rates of protein translation and photosynthetic performance are restricted by low temperatures. As temperatures increased, evidence of heat stress was observed in the photosystem, characterized by a relative down-regulation of the Photosystem II oxygen evolving complex and ATP synthase. Acclimation to elevated warming (28°C) revealed a substantial alteration to carbon metabolism. Here, E. huxleyi made use of the glyoxylate cycle and succinate metabolism to optimize carbon use, maintain growth and maximize ATP production in heat-damaged mitochondria, enabling cultures to maintain growth at levels significantly higher than those recorded in the control (17°C). Based on the metabolic changes observed, we can predict that warming may benefit photosynthetic carbon fixation by E. huxleyi in the sub-optimal to optimal thermal range. Past the thermal optima, increasing rates of respiration and costs of repair will likely constrain growth, causing a possible decline in the contribution of this species to the oceanic carbon sink depending on the evolvability of these temperature thresholds

Nano-pollutants – big impact? Investigating the ecotoxicological effects of nanomaterials in our oceans

Engineered nanomaterials (NMs) used for industrial and commercial applications, represent an emerging contaminant of environmental concern. Due to their widespread use, their entry into the environment is believed inevitable, where the ocean represents the sink for contaminants entered into the aquatic environment. In this thesis new insight is provided on the likely environment risk of engineered NMs towards marine microbial organisms which represent the base of the marine food web and play major roles in global climatic and biogeochemical processes. Three commonly used NMs with clear pathways into the aquatic environment were selected for study; silver nanoparticles (AgNPs), titanium dioxide (nTiO2) and cerium oxide (nCeO2). Preliminary investigation exposing a natural phytoplankton community to AgNPs identified the marine cyanobacterium Prochlorococcus as particularly sensitive to NMs, and hence the model Prochlorococcus sp. MED4 was selected for use in ecotoxicity assessments. Toxicity testing and subsequent investigation of toxic mechanisms revealed varying impacts of metal-based NMs such as AgNPs, and metal oxide NMs upon Prochlorococcus, largely determined by their respective fate and behaviour upon entry into saline media. In chapter 2, AgNPs were observed to exert significant cell declines upon Prochlorococcus via the release of toxic silver ions and superoxide. This perturbation was associated with a significant alteration to the cellular proteome and was irreversible in the longer-term. However, cell declines were mitigated by increasing cell density likely due to an increase in production of superoxide dismutase at higher cell numbers. Significant cell declines were observed at concentrations ≥10 μg L-1 under natural conditions, representing the upper limit of AgNPs predicted in the environment. Hence, it is believed that negative impacts of AgNPs upon marine microbial species is only likely in hotspots of contamination. In chapter 3, the potential impacts of metal oxide NMs (nTiO2 and nCeO2) were investigated. Here, little impact upon Prochlorococcus was recorded in extended exposure (240 h) except at extremely high concentrations (100 mg L-1). Temporary declines were observed in the short-term (≤72 h) and were associated with the heteroaggregation and co-precipitation with nanoparticles which were observed to aggregate rapidly upon entry into seawater, as confirmed by dynamic light scattering (DLS) and fluorescent microscopy. The key role of physical interactions in driving cell declines was further supported by shotgun proteomic analysis of Prochlorococcus exposed to nTiO2 (100 μg L-1), revealing no significant alteration to the cellular or exo- proteome. Effective protocols were established to extract and characterise nTiO2 utilised in consumer products such as cosmetics and sunscreen. Use of nTiO2 extracted from consumer sunscreen in exposures with natural marine microbial communities, found negligible impact upon the structure and diversity of prokaryotic or eukaryotic communities. Hence the current environmental risk of nTiO2 and nCeO2 towards marine microbial species is believed low. In the final experimental chapter 4, in collaboration with an industrial partner, the effectiveness of novel nCeO2 antifouling surface coatings was examined by use of amplicon sequencing, nutrient analysis and 3D microscopic imaging. Investigation revealed negligible impact of the addition of nCeO2 upon biofilm community structure, however nutrient analysis suggested a slight reduction in biofouling in the presence of nanoparticles

An ion gating, bunching, and potential re-referencing unit

A novel design to achieve the gating, bunching, and potential re-referencing of an ion beam, suitable for use in a photofragment spectrometer, is presented. The device simultaneously performs all three functions in a simple, compact, and easily aligned unit. It requires only a single digital signal and one high voltage supply for operation, and provides higher flux density than previous designs. The unit uses lensing to perform beam gating, an approach which has not been reported previously. The design does not require grids, and does not introduce divergence into the ion beam. Experimental results for the combined gating, bunching, and re-referencing unit are presented, and compared with modeled performance.This work is funded by a Major Equipment Grant from the Australian National University. One of the authors (E.H.R.) is the recipient of an Australian Postgraduate Award

Fast 1 kV metal-oxide-semiconductor field-effect transistor switch

A fast, high-voltage switch based on cheap and readily available components is described. This simple circuit can switch 1 kV to ground with a fall time of ∼2.5 ns, and has proved a cost-effective means of driving electrostatic gating and rereferencing devices in pulsed ion-beam experiments.This work is funded by a Major Equipment Grant from the Australian National University. One of the authors (E.H.R.) is the recipient of an Australian Postgraduate Award

New magnetic dipole transition of the oxygen molecule: Bʹ³Πg←X ³Σg⁻(0,0)

Through the use of isotopically pure gas at a temperature of 77 K, a weak photoabsorption band of ¹⁶O₂ is found near 1856 Å, underlying the stronger Schumann–Runge (SR) band B³Σ−u←X³Σ−g(8,0). The location, structure, and intensity of this new band are consistent with expectation for the magnetic dipole transitionB′ ³Πg←X³Σ−g(0,0), where the designation B′ is chosen to represent the II ³Πg valence state. This electronic transition contributes to the “excess absorption” underlying the SR bands [B. R. Lewis, S. T. Gibson, and E. H. Roberts, J. Chem. Phys. 115, 245 (2001)]