Structural latches for modular assembly of spacecraft and space mechanisms

Latching techniques are changing from early approaches due to the advent of berthing technology. Latch selection for a given interface may be conducted by evaluating candidate capabilities which meet functional interface requirements. A judgment criteria system is presented along with an example of its use in choosing the Rollerscrew Structural Latch (RSL) for the NASA Flat Plate Interface Prototype (FPIP). Details are given on Rollerscrew operation, design, and development difficulties. A test plan is also outlined for the RSL and FPIP

A study of information & knowledge generated during engineering design meetings

During the design process, there is a wealth of information generated, and although it may not be obvious at the time, this information can be extremely useful at a later instance when it may be no longer available. Many information capture solutions utilise tools such as video and media capture, incorporating the idea that if you capture all information then you will not miss anything. However, this creates another problem. Not all the information captured will be useful, therefore how can you distinguish the information that is useful from information that is not? The challenge many organisations face is how to capture and store valuable informal information in a way that is both simple and efficient, whilst remaining unobtrusive to the designers involved and without inhibiting the design activities. Through the undertaking of a series of case studies and test scenarios, it is possible to observe, identify and evaluate the various degrees of information and knowledge being generated and passed amongst design engineering teams whilst performing design activities in meeting situations. Using multi-media recording equipment and observation techniques, insight can be gained into the decision making process design engineering teams encounter during the course of a design project, and thus it is possible to evaluate where improved techniques can be applied to enhance the recording of information for re-use

Theory of cooling by flow through narrow pores

We consider the possibility of adding a stage to a dilution refrigerator to provide additional cooling by ``filtering out'' hot atoms. Three methods are considered: 1) Effusion, where holes having diameters larger than a mean-free path allow atoms to pass through easily; 2) Particle waveguide-like motion using very narrow channels that greatly restrict the quantum states of the atoms in a channel. 3) Wall-limited diffusion through channels, in which the wall scattering is disordered so that local density equilibrium is established in a channel. We assume that channel dimension are smaller than the mean-free path for atom-atom interactions. The particle waveguide and the wall-limited diffusion methods using channels on order of the de Broglie wavelength give cooling. Recent advances in nano-filters give this method some hope of being practical.Comment: 10 pages, 3 figures. Corrected typos and made some minor wording change

Deciphering the Mechanism of E. coli tat Protein Transport: Kinetic Substeps and Cargo Properties

The Escherichia coli twin-arginine translocation (Tat) system transports fully folded and assembled proteins across the inner membrane into the periplasmic space. The E. coli Tat machinery minimally consists of three integral membrane proteins: TatA, TatB and TatC. A popular model of Tat translocation is that cargo first interacts with a substrate binding complex composed of TatB and TatC and then is transported across the inner membrane through a channel comprised primarily of TatA. The most common method for observing the kinetics of Tat transport, a protease protection assay, lacks the ability to distinguish between individual transport sub-steps and is limited by the inability to observe translocation in real-time. Therefore, a real-time FRET based assay was developed to observe interactions between the cargo protein pre-SufI, and its initial binding site, the TatBC complex. The cargo was found to first associate with the TatBC complex, and then, in the presence of a membrane potential (∆psi), migrate away from the initial binding site after a 20-45 second delay. Since cargo migration away from the TatBC complex was not directly promoted by the presence of a ∆psi, the delay likely represents some preparatory step that results in a transport competent translocon. In addition, the Tat system has long been identified as a potential biotechnological tool for protein production. However, much is still unknown about which cargos are suitable for transport by the Tat system. To probe the Tat system’s ability to transport substrates of different sizes and shapes, 18 different cargos were generated using the natural Tat substrate pre-SufI as a base. Transport efficiencies for these cargos indicate that not only is the Tat machinery’s ability to transport substrates determined by the protein’s molecular weight, as well as by its dimensions. In total, these results suggest a dynamic translocon that undergoes functionally significant, ∆psi-dependent changes during translocation. Moreover, not every protein cargo can be directed through the Tat translocon by a Tat signal peptide, and this selectivity is not only related to the overall size of the protein, but also dependent on shape

Multifrequency EPR Studies of [Cu^(1.5)Cu^(1.5)]+ for Cu_2(μ-NR_2)_2 and Cu_2(μ-PR_2)_2 Diamond Cores

Multifrequency electron paramagnetic resonance (EPR) spectroscopy is used to explore the electronic structures of a series of dicopper complexes of the type {(LXL)Cu}_2^+. These complexes contain two four-coordinate copper centers of highly distorted tetrahedral geometries linked by two [LXL]^− ligands featuring bridging amido or phosphido ligands and associated thioether or phosphine chelate donors. Specific chelating [LXL]^− ligands examined in this study include bis(2-tert-butylsulfanylphenyl)amide (SNS), bis(2-di-iso-butylphosphinophenyl)amide (PNP), and bis(2-di-iso-propylphosphinophenyl)phosphide (PPP). To better map the electronic coupling to copper, nitrogen, and phosphorus in these complexes, X-, S-, and Q-band EPR spectra have been obtained for each complex. The resulting EPR parameters implied by computer simulation are unusual for typical dicopper complexes and are largely consistent with previously published X-ray absorption spectroscopy and density functional theory data, where a highly covalent {Cu_2(μ-XR_2)_2}^+ diamond core has been assigned in which removal of an electron from the neutral {Cu_2(μ-XR_2)_2} can be viewed as ligand-centered to a substantial degree. To our knowledge, this is the first family of dicopper diamond core model complexes for which the compendium of X-, S-, and Q-band EPR spectra have been collected for comparison to Cu_A

A Cu\u3csub\u3e4\u3c/sub\u3eS Model for the Nitrous Oxide Reductase Active Sites Supported Only by Nitrogen Ligands

To model the (His)7Cu4Sn (n = 1 or 2) active sites of nitrous oxide reductase, the first Cu4(μ4-S) cluster supported only by nitrogen donors has been prepared using amidinate supporting ligands. Structural, magnetic, spectroscopic, and computational characterization is reported. Electrochemical data indicates that the 2-hole model complex can be reduced reversibly to the 1-hole state and irreversibly to the fully reduced state

Environmental Racism: Using Environmental Planning to Lift People Out of Poverty, and Re-shape the Effects of Climate Change & Pollution in Communities of Color,

In the mid-1900s the United States began to see a rise in concern for environmental awareness issues. In the early days the movement focused on things like clean air, water and pollution but by the 1970s-1990s many prominent environmental awareness groups began to form focused on the idea that in order to avert climate change the principal goal needed to be to reduce global greenhouse gas emissions. In 1987 a report was released called Toxic Waste and Race, which outlined an intimate link between the placement of environmental hazardous waste sites in communities of color, and greater instances of polluted air, with contaminated water and soil in those communities as well. The concept of “Environmental Justice” soon formed with advocates labelling the above trend to disproportionately burden minority communities with environmentally harmful industries or practices “Environmental Racism.