On geometry and kinematics of abrasive processes: The theory of aggressiveness

Due to the stochastic nature of the abrasive-tool topography, abrasive processes are difficult to model and quantify. In contrast, their macro geometry and kinematics are usually well defined and straightforwardly controlled on machine tools. To reconcile this seeming contradiction, a novel unifying modelling framework is defined through the theory of aggressiveness. It encompasses the arbitrary geometry and kinematics of a workpiece moving relative to an abrasive surface. The key parameter is the point-aggressiveness, which is a dimensionless scalar quantity based on the vector field of relative velocity and the vector field of abrasive-surface normals. This fundamental process parameter relates directly to typical process outputs such as specific energy, abrasive-tool wear and surface roughness. The theory of aggressiveness is experimentally validated by its application to a diverse array of abrasive processes, including grinding, diamond truing and dressing, where the aggressiveness number is correlated with the aforementioned measured process outputs

Optimierung von Schleif- und Abrichtprozessen mit Hilfe der Theorie der Aggressivit\ue4t: Fallstudien aus der Praxis

In den ersten sechzig Jahren der Schleifforschung (1914-1974) wurden verschiedene dimensionslose Parameter eingef\ufchrt, um die grundlegende Mechanik eines Schleifkontakts zu beschreiben. Sp\ue4ter wurden diese Parameter durch verschiedene Spandickenmodelle ersetzt, die eine schwierige und oft uneindeutige Quantifizierung der Schleifscheibentopographie erforderten. Der Ansatz der Grundprinzipien ist vor kurzem durch die gro fe vereinheitlichende Theorie der Aggressivit\ue4t und die praktische Aggressivit\ue4tszahl wieder aufgetaucht. Diese ist ein dimensionsloser Parameter, der sich bei der Optimierung jedes beliebigen Schleifprozesses, einschlie flich Schleifen und Abrichten, als leistungsf\ue4hig erwiesen hat. Die Aggressivit\ue4tszahl erfreut sich inzwischen einer gr\uf6 feren Beliebtheit und wird verwendet, da sie die grundlegende Prozessgeometrie und -kinematik erfasst und gleichzeitig eine Quantifizierung der Schleifscheibentopographie \ufcberfl\ufcssig macht. In diesem Beitrag wird die Verwendung der dimensionslosen Aggressivit\ue4tszahl in mehreren Fallstudien aus der realen Produktion untersucht. Dabei wird gezeigt, wie das Konzept zur Optimierung industrieller Prozesse eingesetzt werden kann, z. B. beim Schleifen von Nocken- und Kurbelwellen, S\ue4gespitzenschleifen, Nutenschleifen, Doppelseitenschleifen und Abrichten von Diamantscheiben

The Complete Genome Sequence of Haloferax volcanii DS2, a Model Archaeon

a key model organism, not only for the study of halophilicity, but also for archaeal biology in general. DS2, the type strain of this species. The genome contains a main 2.848 Mb chromosome, three smaller chromosomes pHV1, 3, 4 (85, 438, 636 kb, respectively) and the pHV2 plasmid (6.4 kb).

Cryogenic Optical Position Encoders for Mechanisms in the JWST Optical Telescope Element Simulator (OSIM)

The JWST Optical Telescope Element Simulator (OSIM) is a configurable, cryogenic, optical stimulus for high fidelity ground characterization and calibration of JWST's flight instruments. OSIM and its associated Beam Image Analyzer (BIA) contain several ultra-precise, cryogenic mechanisms that enable OSIM to project point sources into the instruments according to the same optical prescription as the flight telescope images stars - correct in focal surface position and chief ray angle. OSIM's and BIA's fifteen axes of mechanisms navigate according to redundant, cryogenic, absolute, optical encoders - 32 in all operating at or below 100 K. OSIM's encoder subsystem, the engineering challenges met in its development, and the encoders' sub-micron and sub-arcsecond performance are discussed

Space Science Opportunities Augmented by Exploration Telepresence

Since the end of the Apollo missions to the lunar surface in December 1972, humanity has exclusively conducted scientific studies on distant planetary surfaces using teleprogrammed robots. Operations and science return for all of these missions are constrained by two issues related to the great distances between terrestrial scientists and their exploration targets: high communication latencies and limited data bandwidth. Despite the proven successes of in-situ science being conducted using teleprogrammed robotic assets such as Spirit, Opportunity, and Curiosity rovers on the surface of Mars, future planetary field research may substantially overcome latency and bandwidth constraints by employing a variety of alternative strategies that could involve: 1) placing scientists/astronauts directly on planetary surfaces, as was done in the Apollo era; 2) developing fully autonomous robotic systems capable of conducting in-situ field science research; or 3) teleoperation of robotic assets by humans sufficiently proximal to the exploration targets to drastically reduce latencies and significantly increase bandwidth, thereby achieving effective human telepresence. This third strategy has been the focus of experts in telerobotics, telepresence, planetary science, and human spaceflight during two workshops held from October 3–7, 2016, and July 7–13, 2017, at the Keck Institute for Space Studies (KISS). Based on findings from these workshops, this document describes the conceptual and practical foundations of low-latency telepresence (LLT), opportunities for using derivative approaches for scientific exploration of planetary surfaces, and circumstances under which employing telepresence would be especially productive for planetary science. An important finding of these workshops is the conclusion that there has been limited study of the advantages of planetary science via LLT. A major recommendation from these workshops is that space agencies such as NASA should substantially increase science return with greater investments in this promising strategy for human conduct at distant exploration sites

Space Science Opportunities Augmented by Exploration Telepresence

Since the end of the Apollo missions to the lunar surface in December 1972, humanity has exclusively conducted scientific studies on distant planetary surfaces using teleprogrammed robots. Operations and science return for all of these missions are constrained by two issues related to the great distances between terrestrial scientists and their exploration targets: high communication latencies and limited data bandwidth. Despite the proven successes of in-situ science being conducted using teleprogrammed robotic assets such as Spirit, Opportunity, and Curiosity rovers on the surface of Mars, future planetary field research may substantially overcome latency and bandwidth constraints by employing a variety of alternative strategies that could involve: 1) placing scientists/astronauts directly on planetary surfaces, as was done in the Apollo era; 2) developing fully autonomous robotic systems capable of conducting in-situ field science research; or 3) teleoperation of robotic assets by humans sufficiently proximal to the exploration targets to drastically reduce latencies and significantly increase bandwidth, thereby achieving effective human telepresence. This third strategy has been the focus of experts in telerobotics, telepresence, planetary science, and human spaceflight during two workshops held from October 3–7, 2016, and July 7–13, 2017, at the Keck Institute for Space Studies (KISS). Based on findings from these workshops, this document describes the conceptual and practical foundations of low-latency telepresence (LLT), opportunities for using derivative approaches for scientific exploration of planetary surfaces, and circumstances under which employing telepresence would be especially productive for planetary science. An important finding of these workshops is the conclusion that there has been limited study of the advantages of planetary science via LLT. A major recommendation from these workshops is that space agencies such as NASA should substantially increase science return with greater investments in this promising strategy for human conduct at distant exploration sites

A metastable equilibrium model for the relative abundances of microbial phyla in a hot spring

Many studies link the compositions of microbial communities to their environments, but the energetics of organism-specific biomass synthesis as a function of geochemical variables has rarely been assessed. We describe a thermodynamic model that integrates geochemical and metagenomic data for biofilms sampled at five sites along a thermal and chemical gradient in the outflow channel of the hot spring known as ‘‘Bison Pool’’ in Yellowstone National Park. The relative abundances of major phyla in individual communities sampled along the outflow channel are modeled by computing metastable equilibrium among model proteins with amino acid compositions derived from metagenomic sequences. Geochemical conditions are represented by temperature and activities of basis species, including pH and oxidation-reduction potential quantified as the activity of dissolved hydrogen. By adjusting the activity of hydrogen, the model can be tuned to closely approximate the relative abundances of the phyla observed in the community profiles generated from BLAST assignments. The findings reveal an inverse relationship between the energy demand to form the proteins at equal thermodynamic activities and the abundance of phyla in the community.Although the metabolisms used by many members of these communities are driven by chemical disequilibria, the results support the possibility that higher-level patterns of chemotrophic microbial ecosystems are shaped by metastable equilibrium states that depend on both the composition of biomass and the environmental conditions

Future Directions for Postdoctoral Training in Cancer Prevention: Insights from a Panel of Experts

Cancer prevention postdoctoral fellowships have existed since the 1970s. The National Cancer Institute facilitated a meeting by a panel of experts in April 2013 to consider four important topics for future directions for cancer prevention postdoctoral training programs: 1) future research needs; 2) underrepresented disciplines; 3) curriculum; and 4) career preparation. Panelists proffered several areas needing more research or emphasis, ranging from computational science to culture. Health care providers, along with persons from non-traditional disciplines such as engineers and lawyers, were among disciplines recognized as being underrepresented in training programs. Curriculum suggestions were that fellows receive training in topics such as leadership and human relations, in addition to learning the principles of epidemiology, cancer biological mechanisms, and behavioral science. For career preparation, there was a clear recognition of the diversity of employment options available besides academic positions, and that program leaders should do more to help fellows identify and prepare for different career paths. The major topics and strategies covered at this meeting can help form the basis for cancer prevention training program leaders to consider modifications or new directions, and keep them current with the changing scientific and employment climate for doctoral degree recipients and postdoctoral fellows

Evolution of Symbiotic Bacteria in the Distal Human Intestine

The adult human intestine contains trillions of bacteria, representing hundreds of species and thousands of subspecies. Little is known about the selective pressures that have shaped and are shaping this community's component species, which are dominated by members of the Bacteroidetes and Firmicutes divisions. To examine how the intestinal environment affects microbial genome evolution, we have sequenced the genomes of two members of the normal distal human gut microbiota, Bacteroides vulgatus and Bacteroides distasonis, and by comparison with the few other sequenced gut and non-gut Bacteroidetes, analyzed their niche and habitat adaptations. The results show that lateral gene transfer, mobile elements, and gene amplification have played important roles in affecting the ability of gut-dwelling Bacteroidetes to vary their cell surface, sense their environment, and harvest nutrient resources present in the distal intestine. Our findings show that these processes have been a driving force in the adaptation of Bacteroidetes to the distal gut environment, and emphasize the importance of considering the evolution of humans from an additional perspective, namely the evolution of our microbiomes