The effects of pH and aluminum on the growth of the acidophilic diatom Asterionella ralfsii var. americana

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/110027/1/lno19913610123.pd

Deployable Optics for CubeSats

Since the beginning of the space age, many structures with different levels of complexity have been proposed for the deployment of equipment such as solar arrays, antennae, and scientific instruments. By increasing the packaging efficiency, stowing during launch and then deploying in orbit provides an opportunity for the improvement of the capabilities of small satellites payloads while maintaining a contained launch volume. The latter is particularly important when considering the launch of future constellations and, in particular, CubeSats where the volume is significantly constrained by the size of the pod. The focus of this work is the development of a camera/telescope barrel ideally suited for a Cassegrain configured space instrument, hosting the primary mirror at one (satellite side) end and the secondary mirror supported by a cruciform element at the other end (aperture). The barrel is stowed and deployed using a telescopic approach with three coaxial large diameter hollow cylinders making up the segments of the barrel. For an optical telescope, one of the most important challenges is in maintaining a highly accurate distance between the optical elements (in this case, primary and secondary mirrors which are positioned with an accuracy of a few micron). Thermo-mechanical distortions due to on orbit temperature variations and any micro-vibration excitation from sources on the spacecraft can cause significant degradation of the optical performance. To maintain the required shape stability, the main structural parts are made in a thermally invariable material and incorporate features to provide alignment and locking out. The large diameter of the structure, and low coefficient of thermal expansion, give the assembly excellent resilience to thermal and micro-vibration disturbances whilst keeping mass to a minimum. This “tube” arrangement also naturally fulfils the light baffling requirements of the telescope. Another significant challenge is the apparatus to drive the sequential deployment of the cylinders. Systems that use lead screws and gears have been proposed, however they present significant complexities and their mass has a substantial impact on the mass budget of the overall assembly. Here, a novel robust and simple wire-driven system is proposed to operate the deployment. The main advantages being the simplicity, light weight, and robustness with respect to severe vibration environments. This article will describe the development of the device and the testing of the proof of concept/qualification model

Control of Ultracold Collisions with Frequency-Chirped Light

We report on ultracold atomic collision experiments utilizing frequency-chirped laser light. A rapid chirp below the atomic resonance results in adiabatic excitation to an attractive molecular potential over a wide range of internuclear separation. This leads to a transient inelastic collision rate which is large compared to that obtained with fixed-frequency excitation. The combination of high efficiency and temporal control demonstrates the benefit of applying the techniques of coherent control to the ultracold domain

Collective dynamics of fermion clouds in cigar-shaped traps

The propagation of zero sound in a spin-polarized Fermi gas under harmonic confinement is studied as a function of the mean-field interactions with a second Fermi gas. A local-density treatment is compared with the numerical solution of the Vlasov-Landau equations for the propagation of density distortions in a trapped two-component Fermi gas at temperature T=0.2 Tf. The response of the gas to the sudden creation of a sharp hole at its centre is also studied numerically.Comment: 15 pages, 6 figure

Broad Feshbach resonance in the 6Li-40K mixture

We study the widths of interspecies Feshbach resonances in a mixture of the fermionic quantum gases 6Li and 40K. We develop a model to calculate the width and position of all available Feshbach resonances for a system. Using the model we select the optimal resonance to study the 6Li/40K mixture. Experimentally, we obtain the asymmetric Fano lineshape of the interspecies elastic cross section by measuring the distillation rate of 6Li atoms from a potassium-rich 6Li/40K mixture as a function of magnetic field. This provides us with the first experimental determination of the width of a resonance in this mixture, Delta B=1.5(5) G. Our results offer good perspectives for the observation of universal crossover physics using this mass-imbalanced fermionic mixture.Comment: 4 pages, 2 figure

Photoassociative Production and Trapping of Ultracold KRb Molecules

We have produced ultracold heteronuclear KRb molecules by the process of photoassociation in a two-species magneto-optical trap. Following decay of the photoassociated KRb*, the molecules are detected using two-photon ionization and time-of-flight mass spectroscopy of KRb$^+$. A portion of the metastable triplet molecules thus formed are magnetically trapped. Photoassociative spectra down to 91 cm$^{-1}$ below the K(4$s$) + Rb (5$p_{1/2}$) asymptote have been obtained. We have made assignments to all eight of the attractive Hund's case (c) KRb* potential curves in this spectral region.Comment: 4 pages, 4 figure