Compliant Metal Enhanced Convection Cooled Reverse-Flow Annular Combustor

A joint Army/NASA program was conducted to design, fabricate, and test an advanced, reverse-flow, small gas turbine combustor using a compliant metal enhanced (CME) convection wall cooling concept. The objectives of this effort were to develop a design method (basic design data base and analysis) for the CME cooling technique and tben demonstrate its application to an advanced cycle, small, reverse-flow combustor with 3000 F (1922 K) burner outlet temperature (BOT). The CME concept offers significant improvements in wall cooling effectiveness resulting in a large reduction in cooling air requirements. Therefore, more air is available for control of burner outlet temperature pattern in addition to the benefit of improved efficiency, reduced emissions, and smoke levels. Rig test results demonstrated the benefits and viability of the CME concept meeting or exceeding the aerothermal performance and liner wall temperature characteristics of similar lower temperature-rise combustors, achieving 0.15 pattern factor at 3000 F (1922 K) BOT, while utilizing approximately 80 percent less cooling air than conventional, film-cooled combustion systems

Robust Probabilistic Inference in Distributed Systems

Probabilistic inference problems arise naturally in distributed systems such as sensor networks and teams of mobile robots. Inference algorithms that use message passing are a natural fit for distributed systems, but they must be robust to the failure situations that arise in real-world settings, such as unreliable communication and node failures. Unfortunately, the popular sum--product algorithm can yield very poor estimates in these settings because the nodes' beliefs before convergence can be arbitrarily different from the correct posteriors. In this paper, we present a new message passing algorithm for probabilistic inference which provides several crucial guarantees that the standard sum--product algorithm does not. Not only does it converge to the correct posteriors, but it is also guaranteed to yield a principled approximation at any point before convergence. In addition, the computational complexity of the message passing updates depends only upon the model, and is independent of the network topology of the distributed system. We demonstrate the approach with detailed experimental results on a distributed sensor calibration task using data from an actual sensor network deployment

Authigenic minerals reflect microbial control on pore waters in a ferruginous analogue

Ferruginous conditions prevailed in the oceans through much of Earth's history. However, minerals recording these conditions remain difficult to interpret in terms of biogeochemical processes prior to lithification. In Lake Towuti, Indonesia, ferruginous sediments are deposited under anoxic sulfate-poor conditions similar to the Proterozoic oceans, allowing the study of mineralogical (trans)formations during microbial diagenesis. Comprehensive pore water geochemistry, high resolution geochemical core profiles, and electron microscopy of authigenic minerals revealed in situ formation of magnetite, millerite, and abundant siderite and vivianite along a 100 m long sequence. Framboidal magnetites represent primary pelagic precipitates, whereas millerite, a sulfide mineral often overlooked under sulfate-poor conditions, shows acicular aggregates entangled with siderite and vivianite resulting from saturated pore waters and continuous growth during burial. These phases act as biosignatures of microbial iron and sulfate reduction, fermentation and methanogenesis, processes clearly traceable in pore water profiles. Variability in metal and organic substrates attests to environment driven processes, differentially sustaining microbial processes along the stratigraphy. Geochemical profiles resulting from microbial activity over 200 kyr after deposition provide constraints on the depth and age of mineral formation within ferruginous records

Authigenic minerals reflect microbial control on pore waters in a ferruginous analogue

Ferruginous conditions prevailed in the oceans through much of Earth’s history. However, minerals recording these conditions remain difficult to interpret in terms of biogeochemical processes prior to lithification. In Lake Towuti, Indonesia, ferruginous sediments are deposited under anoxic sulfate-poor conditions similar to the Proterozoic oceans, allowing the study of mineralogical (trans)formations during microbial diagenesis. Comprehensive pore water geochemistry, high resolution geochemical core profiles, and electron microscopy of authigenic minerals revealed in situ formation of magnetite, millerite, and abundant siderite and vivianite along a 100 m long sequence. Framboidal magnetites represent primary pelagic precipitates, whereas millerite, a sulfide mineral often overlooked under sulfate-poor conditions, shows acicular aggregates entangled with siderite and vivianite resulting from saturated pore waters and continuous growth during burial. These phases act as biosignatures of microbial iron and sulfate reduction, fermentation and methanogenesis, processes clearly traceable in pore water profiles. Variability in metal and organic substrates attests to environment driven processes, differentially sustaining microbial processes along the stratigraphy. Geochemical profiles resulting from microbial activity over 200 kyr after deposition provide constraints on the depth and age of mineral formation within ferruginous records

Evolution and overview of Linked USDL

For more than 10 years, research on service descriptions has mainly studied software-based services and provided languages such as WSDL, OWL-S, WSMO for SOAP, and hREST for REST. Nonetheless, recent developments from service management (e.g., ITIL and COBIT) and cloud computing (e.g. Software-as-a-Service) have brought new re- quirements to service descriptions languages: the need to also model business services and account for the multi-faceted nature of services. Business-orientation, co-creation, pricing, legal aspects, and security issues are all elements which must also be part of service descriptions. While ontologies such as e service and e value provided a first modeling attempt to capture a business perspective, concerns on how to contract services and the agreements entailed by a contract also need to be taken into account. This has for the most part been disregarded by the e family of ontologies. In this paper, we review the evolution and provide an overview of Linked USDL, a comprehensive language which provides a (multi-faceted) description to enable the commercialization of (business and technical) services over the web

Nonlinear lattice model of viscoelastic Mode III fracture

We study the effect of general nonlinear force laws in viscoelastic lattice models of fracture, focusing on the existence and stability of steady-state Mode III cracks. We show that the hysteretic behavior at small driving is very sensitive to the smoothness of the force law. At large driving, we find a Hopf bifurcation to a straight crack whose velocity is periodic in time. The frequency of the unstable bifurcating mode depends on the smoothness of the potential, but is very close to an exact period-doubling instability. Slightly above the onset of the instability, the system settles into a exactly period-doubled state, presumably connected to the aforementioned bifurcation structure. We explicitly solve for this new state and map out its velocity-driving relation

Role of confined phonons in thin film superconductivity

We calculate the critical temperature $T_c$ and the superconducting energy gaps $\Delta_n$ of a thin film superconductor system, where $\Delta_n$ is the superconducting energy gap of the $n$-th subband. Since the quantization of both the electron energy and phonon spectrum arises due to dimensional confinement in one direction, the effective electron-electron interaction mediated by the quantized confined phonons is different from that mediated by the bulk phonon, leading to the modification of $T_c$ in the thin film system. We investigate the dependence of $T_c$ and $\Delta_n$ on the film thickness $d$ with this modified interaction.Comment: 4 pages, 2 figure

Effects of crack tip geometry on dislocation emission and cleavage: A possible path to enhanced ductility

We present a systematic study of the effect of crack blunting on subsequent crack propagation and dislocation emission. We show that the stress intensity factor required to propagate the crack is increased as the crack is blunted by up to thirteen atomic layers, but only by a relatively modest amount for a crack with a sharp 60$^\circ$ corner. The effect of the blunting is far less than would be expected from a smoothly blunted crack; the sharp corners preserve the stress concentration, reducing the effect of the blunting. However, for some material parameters blunting changes the preferred deformation mode from brittle cleavage to dislocation emission. In such materials, the absorption of preexisting dislocations by the crack tip can cause the crack tip to be locally arrested, causing a significant increase in the microscopic toughness of the crack tip. Continuum plasticity models have shown that even a moderate increase in the microscopic toughness can lead to an increase in the macroscopic fracture toughness of the material by several orders of magnitude. We thus propose an atomic-scale mechanism at the crack tip, that ultimately may lead to a high fracture toughness in some materials where a sharp crack would seem to be able to propagate in a brittle manner. Results for blunt cracks loaded in mode II are also presented.Comment: 12 pages, REVTeX using epsfig.sty. 13 PostScript figures. Final version to appear in Phys. Rev. B. Main changes: Discussion slightly shortened, one figure remove