35,347 research outputs found
Constitutive response of Rene 80 under thermal mechanical loads
The applicability of a classical constitutive model for stress-strain analysis of a nickel base superalloy, Rene' 80, in the gas turbine thermomechanical fatigue (TMF) environment is examined. A variety of tests were conducted to generate basic material data and to investigate the material response under cyclic thermomechanical loading. Isothermal stress-strain data were acquired at a variety of strain rates over the TMF temperature range. Creep curves were examined at 2 temperature ranges, 871 to 982 C and 760 to 871 C. The results provide optimism on the ability of the classical constitutive model for high temperature applications
Quantifying fusion born ion populations in magnetically confined plasmas using ion cyclotron emission
Ion cyclotron emission (ICE) offers unique promise as a diagnostic of the
fusion born alpha-particle population in magnetically confined plasmas.
Pioneering observations from JET and TFTR found that ICE intensity
scales approximately linearly with the measured neutron flux from fusion
reactions, and with the inferred concentration, , of fusion-born
alpha-particles confined within the plasma. We present fully nonlinear
self-consistent kinetic simulations that reproduce this scaling for the first
time. This resolves a longstanding question in the physics of fusion
alpha-particle confinement and stability in MCF plasmas. It confirms the
magnetoacoustic cyclotron instability (MCI) as the likely emission mechanism
and greatly strengthens the basis for diagnostic exploitation of ICE in future
burning plasmas
Adaptive laser link reconfiguration using constraint propagation
This paper describes Harris AI research performed on the Adaptive Link Reconfiguration (ALR) study for Rome Lab, and focuses on the application of constraint propagation to the problem of link reconfiguration for the proposed space based Strategic Defense System (SDS) Brilliant Pebbles (BP) communications system. According to the concept of operations at the time of the study, laser communications will exist between BP's and to ground entry points. Long-term links typical of RF transmission will not exist. This study addressed an initial implementation of BP's based on the Global Protection Against Limited Strikes (GPALS) SDI mission. The number of satellites and rings studied was representative of this problem. An orbital dynamics program was used to generate line-of-site data for the modeled architecture. This was input into a discrete event simulation implemented in the Harris developed COnstraint Propagation Expert System (COPES) Shell, developed initially on the Rome Lab BM/C3 study. Using a model of the network and several heuristics, the COPES shell was used to develop the Heuristic Adaptive Link Ordering (HALO) Algorithm to rank and order potential laser links according to probability of communication. A reduced set of links based on this ranking would then be used by a routing algorithm to select the next hop. This paper includes an overview of Constraint Propagation as an Artificial Intelligence technique and its embodiment in the COPES shell. It describes the design and implementation of both the simulation of the GPALS BP network and the HALO algorithm in COPES. This is described using a 59 Data Flow Diagram, State Transition Diagrams, and Structured English PDL. It describes a laser communications model and the heuristics involved in rank-ordering the potential communication links. The generation of simulation data is described along with its interface via COPES to the Harris developed View Net graphical tool for visual analysis of communications networks. Conclusions are presented, including a graphical analysis of results depicting the ordered set of links versus the set of all possible links based on the computed Bit Error Rate (BER). Finally, future research is discussed which includes enhancements to the HALO algorithm, network simulation, and the addition of an intelligent routing algorithm for BP
Testing a Simplified Version of Einstein's Equations for Numerical Relativity
Solving dynamical problems in general relativity requires the full machinery
of numerical relativity. Wilson has proposed a simpler but approximate scheme
for systems near equilibrium, like binary neutron stars. We test the scheme on
isolated, rapidly rotating, relativistic stars. Since these objects are in
equilibrium, it is crucial that the approximation work well if we are to
believe its predictions for more complicated systems like binaries. Our results
are very encouraging.Comment: 9 pages (RevTeX 3.0 with 6 uuencoded figures), CRSR-107
Immune compromise in HIV-1/HTLV-1 coinfection with paradoxical resolution of CD4 lymphocytosis during antiretroviral therapy: a case report
Human immunodeficiency virus type-1 (HIV-1) and human T lymphotropic virus type-1 (HTLV-1) infections have complex effects on adaptive immunity, with specific tropism for, but contrasting effects on, CD4 T lymphocytes: depletion with HIV-1, proliferation with HTLV-1. Impaired T lymphocyte function occurs early in HIV-1 infection but opportunistic infections (OIs) rarely occur in the absence of CD4 lymphopenia. In the unusual case where a HIV-1 infected individual with a high CD4 count presents with recurrent OIs, a clinician is faced with the possibility of a second underlying comorbidity. We present a case of pseudo-adult T cell leukemia/lymphoma (ATLL) in HIV-1/HTLV-1 coinfection where the individual fulfilled Shimoyama criteria for chronic ATLL and had pulmonary Mycobacterium kansasii, despite a high CD4 lymphocyte count. However, there was no evidence of clonal T-cell proliferation by T-cell receptor gene rearrangement studies nor of monoclonal HTLV-1 integration by high-throughput sequencing. Mutually beneficial interplay between HIV-1 and HTLV-1, maintaining high level HIV-1 and HTLV-1 viremia and proliferation of poorly functional CD4 cells despite chronicity of infection is a postulated mechanism. Despite good microbiological response to antimycobacterial therapy, the patient remained systemically unwell with refractory anemia. Subsequent initiation of combined antiretroviral therapy led to paradoxical resolution of CD4 T lymphocytosis as well as HIV-1 viral suppression and decreased HTLV-1 proviral load. This is proposed to be the result of attenuation of immune activation post-HIV virological control. This case illustrates the importance of screening for HTLV-1 in HIV-1 patients with appropriate clinical presentation and epidemiological risk factors and explores mechanisms for the complex interactions on HIV-1/HTLV-1 adaptive immunity
Stability and collapse of rapidly rotating, supramassive neutron stars: 3D simulations in general relativity
We perform 3D numerical simulations in full general relativity to study the
stability of rapidly rotating, supramassive neutron stars at the mass-shedding
limit to dynamical collapse. We adopt an adiabatic equation of state with
and focus on uniformly rotating stars. We find that the onset of
dynamical instability along mass-shedding sequences nearly coincides with the
onset of secular instability. Unstable stars collapse to rotating black holes
within about one rotation period. We also study the collapse of stable stars
which have been destabilized by pressure depletion (e.g. via a phase
transition) or mass accretion. In no case do we find evidence for the formation
of massive disks or any ejecta around the newly formed Kerr black holes, even
though the progenitors are rapidly rotating.Comment: 16 pages, to appear in Phys. Rev.
Implementation of the FAA research and development electromagnetic database
The Idaho National Engineering Laboratory (INEL) has been assisting the FAA in developing a database of information about lightning. The FAA Research and Development Electromagnetic Database (FRED) will ultimately contain data from a variety of airborne and ground-based lightning research projects. An outline of the data currently available in FRED is presented. The data sources which the FAA intends to incorporate into FRED are listed. In addition, it describes how the researchers may access and use the FRED menu system
What cost reslience?
Air traffic management research lacks a framework for modelling the cost of resilience during disturbance. There is no universally accepted metric for cost resilience. The design of such a framework is presented and the modelling to date is reported. The framework allows performance assessment as a function of differential stakeholder uptake of strategic mechanisms designed to mitigate disturbance. Advanced metrics, cost- and non-cost-based, disaggregated by stakeholder subtypes, will be deployed. A new cost resilience metric is proposed
Controller time and delay costs - a trade-off analysis
Air traffic controller shortages remain a significant challenge in European ATM. Comparing different rules, we quantify the cost effectiveness of adding controller hours to Area Control Centre regulations to avert the delay cost impact on airlines. Typically, adding controller hours results in a net benefit. Distributions of delay duration and aircraft weight play an important role in determining the total cost of a regulation. Errors are likely to be incurred when analysing performance based on average delay values, particularly at the disaggregate level
ComplexityCosts D4.5 - Final Technical Report
Using traffic and passenger itinerary data for the European network, the cost resilience of four mechanisms, with phased stakeholder uptake, has been assessed under explicit, local and disperse disturbance: industrial action and weather. A novel cost resilience metric has demonstrated logical properties and captured cost impacts sensitively. Of these mechanisms, only A-CDM has been cost-benefit analysed in SESAR, yet the other three each demonstrate particular utility. Flight-, passenger- and cost-centric metrics are deployed to assess the mechanisms, with fully costed results presented, based on extensive industry consultation. Initial work on assessing mechanism payback periods has begun
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