Feasibility and Performance of the Microwave Thermal Rocket Launcher

Beamed-energy launch concepts employing a microwave thermal thruster are feasible in principle, and microwave sources of sufficient power to launch tons into LEO already exist. Microwave thermal thrusters operate on an analogous principle to nuclear thermal thrusters, which have experimentally demonstrated specific impulses exceeding 850 seconds. Assuming such performance, simple application of the rocket equation suggests that payload fractions of 10% are possible for a single stage to orbit (SSTO) microwave thermal rocket. We present an SSTO concept employing a scaled X-33 aeroshell. The flat aeroshell underside is covered by a thin-layer microwave absorbent heat-exchanger that forms part of the thruster. During ascent, the heat-exchanger faces the microwave beam. A simple ascent trajectory analysis incorporating X-33 aerodynamic data predicts a 10% payload fraction for a 1 ton craft of this type. In contrast, the Saturn V had 3 non-reusable stages and achieved a payload fraction of 4%

Influence of human pressures on large river structure and function

A large river study was conducted as part of the Cross Departmental Research Pool (CDRP) ecological integrity project to (i) provide an overview of the macroinvertebrate faunas of large rivers, including those in deep-water habitats, and (ii) to elucidate links between these faunas, river function and anthropogenic stressors. Eleven sites on 6th-order or 7th-order rivers were sampled; four in the South Island and seven in the North Island. We measured (i) macroinvertebrate communities colonising wood, riffles (where present), littoral habitats (1.5 m deep) (ii) ecosystem metabolism using a single-station open-channel approach based on natural changes in dissolved oxygen concentration over a 24-hour period, and (iii) wood and cellulose breakdown. Relationships were investigated between these response variables and reach-scale assessments of habitat quality, underlying upstream and segment environmental variables provided in the Freshwater Environments of New Zealand (FWENZ) database, and anthropogenic pressure variables provided by the Waters of National Importance (WONI) database

Seeing More than Orange: Organizational Respect and Positive Identity Transformation in a Prison Context

This paper develops grounded theory on how receiving respect at work enables individuals to engage in positive identity transformation and the resulting personal and work-related outcomes. A company that employs inmates at a state prison to perform professional business-to-business marketing services provided a unique context for data collection. Our data indicate that inmates experienced respect in two distinct ways, generalized and particularized, which initiated an identity decoupling process that allowed them to distinguish between their inmate identity and their desired future selves and to construct transitional identities that facilitated positive change. The social context of the organization provided opportunities for personal and social identities to be claimed, respected, and granted, producing social validation and enabling individuals to feel secure in their transitional identities. We find that security in personal identities produces primarily performance-related outcomes, whereas security in the company identity produces primarily well-being-related outcomes. Further, these two types of security together foster an integration of seemingly incompatible identities—”identity holism”—as employees progress toward becoming their desired selves. Our work suggests that organizations can play a generative role in improving the lives of their members through respect-based processes

Anomalous diffusion and the Moses effect in a model of aging

We decompose the anomalous diffusive behavior found in a model of aging into its fundamental constitutive causes. The model process is a sum of increments that are iterates of a chaotic dynamical system, the Pomeau-Manneville map. The increments can have long-time correlations, fat-tailed distributions and be non-stationary. Each of these properties can cause anomalous diffusion through what is known as the Joseph, Noah and Moses effects, respectively. The model can have either sub- or super-diffusive behavior, which we find is generally due to a combination of the three effects. Scaling exponents quantifying each of the three constitutive effects are calculated using analytic methods and confirmed with numerical simulations. They are then related to the scaling of the distribution of the process through a scaling relation. Finally, the importance of the Moses effect in the anomalous diffusion of experimental systems is discussed.Comment: This is an author-created, un-copyedited version of an article accepted for publication in the New Journal of Physics. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.1088/1367-2630/aaeea

The Microwave Thermal Thruster Concept

The microwave thermal thruster heats propellant via a heat-exchanger then expands it through a rocket nozzle to produce thrust. The heat-exchanger is simply a microwave-absorbent structure through which propellant flows in small channels. Nuclear thermal thrusters are based on an analogous principle, using neutrons rather than microwaves, and have experimentally demonstrated specific impulses exceeding 850 seconds. A microwave equivalent will likely have a similar specific impulse, since both nuclear and microwave thermal thrusters are ultimately constrained by material thermal limits, rather than the energy-density limits of chemical propellants. We present the microwave thermal thruster concept by characterizing a novel variation for beamed-energy launch. In reducing the thruster concept to practice, the enabling physical process is microwave absorption by refractory materials, and we examine semiconductor and susceptor-based approaches to achieving this absorption within the heat-exchanger structure

Transfer of Sulfur from IscS to IscU during Fe/S Cluster Assembly

The cysteine desulfurase enzymes NifS and IscS provide sulfur for the biosynthesis of Fe/S proteins. NifU and IscU have been proposed to serve as template or scaffold proteins in the initial Fe/S cluster assembly events, but the mechanism of sulfur transfer from NifS or IscS to NifU or IscU has not been elucidated. We have employed [35S]cysteine radiotracer studies to monitor sulfur transfer between IscS and IscU from Escherichia coli and have used direct binding measurements to investigate interactions between the proteins. IscS catalyzed transfer of 35S from [35S]cysteine to IscU in the absence of additional thiol reagents, suggesting that transfer can occur directly and without involvement of an intermediate carrier. Surface plasmon resonance studies and isothermal titration calorimetry measurements further revealed that IscU binds to IscS with high affinity (Kd ~2 µM) in support of a direct transfer mechanism. Transfer was inhibited by treatment of IscU with iodoacetamide, and 35S was released by reducing reagents, suggesting that transfer of persulfide sulfur occurs to cysteinyl groups of IscU. A deletion mutant of IscS lacking C-terminal residues 376-413 (IscSDelta 376-413) displayed cysteine desulfurase activity similar to the full-length protein but exhibited lower binding affinity for IscU, decreased ability to transfer 35S to IscU, and reduced activity in assays of Fe/S cluster assembly on IscU. The findings with IscSDelta 376-413 provide additional support for a mechanism of sulfur transfer involving a direct interaction between IscS and IscU and suggest that the C-terminal region of IscS may be important for binding IscU