Rubidium and cesium frequency standards status and performance on the GPS program

The on-oribt operational performance of the frequency standards on the Global Positioning System (GPS) 1 to 10 NAVSTAR satellites are discussed. The history of the Rb frequency standards showing the improvements incorporated at various stages of the program and the corresponding results are presented. Also presented is the operational history of the NAVSTAR cesium frequency standards. The frequency standards configuration data presented covers the chronology of events from the concept validation satellites, NAVSTAR 1 to 10, starting in 1978 to the present, including the configurations of clocks to be used on the GPS Production Program. Data are presented showing the results of long-term laboratory testing of a production Rb frequency standard with the necessary data taken to calculate Delta F, drift, time error, and Allan variance

Production of gaseous fuel by pyrolysis of municipal solid waste

Pilot plant tests were conducted on a simulated solid waste which was a mixture of shredded newspaper, wood waste, polyethylene plastics, crushed glass, steel turnings, and water. Tests were conducted at 1400 F in a lead-bath pyrolyser. Cold feed was deaerated by compression and was dropped onto a moving hearth of molten lead before being transported to a sealed storage container. About 80 percent of the feed's organic content was converted to gaseous products which contain over 90 percent of the potential waste energy; 12 percent was converted to water; and 8 percent remained as partially pyrolyzed char and tars. Nearly half of the carbon in the feed is converted to benzene, toluene and medium-quality fuel gas, a potential credit of over $25 per ton of solid waste. The system was shown to require minimal preprocessing and less sorting then other methods

Within- and between-subject consistency of perceptual segmentation in periodic noise: A combined behavioral tapping and EEG study

The human auditory system is capable of learning unstructured acoustic patterns that occur repeatedly. While most previous studies on perceptual learning focused on seamless pattern repetitions, our study included several presentation formats, which are more typical for memory tasks (involving temporal delays or irrelevant information between pattern presentations), and probed active recognition of learned patterns more directly. We adapted an established implicit learning paradigm and presented three groups of listeners with the same acoustic patterns in different presentation formats, i.e., either back-to-back, separated by a silent interval or by a masker sound. Participants additionally completed an unexpected memory test after the learning phase. We found substantial learning in all groups, measured indirectly via the increased sensitivity in a perceptual task for patterns that occurred repeatedly (compared to patterns that occurred only once) and more directly via above-chance recognition performance in the memory test. Pattern learning and recognition were robust across presentation formats. Therefore, we propose that similar mechanisms might underlie memory formation for initially unfamiliar sounds in everyday listening situations. Moreover, memories for unstructured acoustic patterns that were acquired implicitly through perceptual learning enable subsequent active recognition

Perceptual learning and recognition of random acoustic patterns

The human auditory system is capable of learning unstructured acoustic patterns that occur repeatedly. While most previous studies on perceptual learning focused on seamless pattern repetitions, our study included several presentation formats, which are more typical for memory tasks (involving temporal delays or irrelevant information between pattern presentations), and probed active recognition of learned patterns more directly. We adapted an established implicit learning paradigm and presented three groups of listeners with the same acoustic patterns in different presentation formats, i.e., either back-to-back, separated by a silent interval or by a masker sound. Participants additionally completed an unexpected memory test after the learning phase. We found substantial learning in all groups, measured indirectly via the increased sensitivity in a perceptual task for patterns that occurred repeatedly (compared to patterns that occurred only once) and more directly via above-chance recognition performance in the memory test. Pattern learning and recognition were robust across presentation formats. Therefore, we propose that similar mechanisms might underlie memory formation for initially unfamiliar sounds in everyday listening situations. Moreover, memories for unstructured acoustic patterns that were acquired implicitly through perceptual learning enable subsequent active recognition

Nano-twining and deformation-induced martensitic transformation in a duplex stainless steel 2205 fabricated by laser powder bed fusion

Duplex stainless steels (DSSs) possess desirable combinations of mechanical properties and excellent corrosion resistance due to their composition and equilibrium microstructure of roughly equivalent fractions of ferrite and austenite. They are used in harsh environments such as marine infrastructures, oil & gas, and paper & pulp industries. Components with complex geometries are often required for these applications. Additive manufacturing (AM) techniques such as laser powder bed fusion (LPBF) can be harnessed to fabricate components with greatest complexity. However, AM fabrication is well-known to promote non-equilibrium microstructures with high dislocation densities and Cr2N precipitates, resulting in inferior ductility. This is generally regarded as a challenge, however, short heat treatments of such as-built microstructures have been shown to attain refined duplex equilibrium microstructures. Recently, annealed LPBF DSS 2205 has been reported to possess strength higher than wrought counterparts and ductility properties better than the as-built state. However, the microstructural phenomena and deformation mechanisms behind these attractive properties remain poorly understood. Through multi-scale microstructural characterization, we show that the improved strength results not only from the hard ferrite phase, but also fine austenite grain size and nanoscale oxide dispersion strengthening. The enhanced ductility may be attributed to a combination of deformation mechanisms including dislocation slip, stacking fault formation, deformation twinning, and a deformation-induced martensitic transformation. We discuss how the level of microstructural complexity and solid-state phase transformations during LPBF and annealing can unlock multiple strengthening mechanisms during tensile deformation. Such fundamental understanding is crucial for designing AM parts with reproducible and optimised mechanical properties

Enhancement of Transition Temperature in FexSe0.5Te0.5 Film via Iron Vacancies

The effects of iron deficiency in FexSe0.5Te0.5 thin films (0.8<x<1) on superconductivity and electronic properties have been studied. A significant enhancement of the superconducting transition temperature (TC) up to 21K was observed in the most Fe deficient film (x=0.8). Based on the observed and simulated structural variation results, there is a high possibility that Fe vacancies can be formed in the FexSe0.5Te0.5 films. The enhancement of TC shows a strong relationship with the lattice strain effect induced by Fe vacancies. Importantly, the presence of Fe vacancies alters the charge carrier population by introducing electron charge carriers, with the Fe deficient film showing more metallic behavior than the defect-free film. Our study provides a means to enhance the superconductivity and tune the charge carriers via Fe vacancy, with no reliance on chemical doping.Comment: 15 pages, 4 figure

Lateral prefrontal cortex is a hub for music production from structural rules to movements

Complex sequential behaviours, such as speaking or playing music, entail flexible rule-based chaining of single acts. However, it remains unclear how the brain translates abstract structural rules into movements. We combined music production with multi-modal neuroimaging to dissociate high-level structural and low-level motor planning. Pianists played novel musical chord sequences on a muted MR-compatible piano by imitating a model hand on screen. Chord sequences were manipulated in terms of musical harmony and context length to assess structural planning, and in terms of fingers used for playing to assess motor planning. A model of probabilistic sequence processing confirmed temporally extended dependencies between chords, as opposed to local dependencies between movements. Violations of structural plans activated the left inferior frontal and middle temporal gyrus, and the fractional anisotropy of the ventral pathway connecting these two regions positively predicted behavioural measures of structural planning. A bilateral fronto-parietal network was instead activated by violations of motor plans. Both structural and motor networks converged in lateral prefrontal cortex, with anterior regions contributing to musical structure building, and posterior areas to movement planning. These results establish a promising approach to study sequence production at different levels of action representation