6,359 research outputs found
OMS FDIR: Initial prototyping
The Space Station Freedom Program (SSFP) Operations Management System (OMS) will automate major management functions which coordinate the operations of onboard systems, elements and payloads. The objectives of OMS are to improve safety, reliability and productivity while reducing maintenance and operations cost. This will be accomplished by using advanced automation techniques to automate much of the activity currently performed by the flight crew and ground personnel. OMS requirements have been organized into five task groups: (1) Planning, Execution and Replanning; (2) Data Gathering, Preprocessing and Storage; (3) Testing and Training; (4) Resource Management; and (5) Caution and Warning and Fault Management for onboard subsystems. The scope of this prototyping effort falls within the Fault Management requirements group. The prototyping will be performed in two phases. Phase 1 is the development of an onboard communications network fault detection, isolation, and reconfiguration (FDIR) system. Phase 2 will incorporate global FDIR for onboard systems. Research into the applicability of expert systems, object-oriented programming, fuzzy sets, neural networks and other advanced techniques will be conducted. The goals and technical approach for this new SSFP research project are discussed here
Compton scattering in strong magnetic fields: Spin-dependent influences at the cyclotron resonance
The quantum electrodynamical (QED) process of Compton scattering in strong
magnetic fields is commonly invoked in atmospheric and inner magnetospheric
models of x-ray and soft gamma-ray emission in high-field pulsars and
magnetars. A major influence of the field is to introduce resonances at the
cyclotron frequency and its harmonics, where the incoming photon accesses
thresholds for the creation of virtual electrons or positrons in intermediate
states with excited Landau levels. At these resonances, the effective cross
section typically exceeds the classical Thomson value by over 2 orders of
magnitude. Near and above the quantum critical magnetic field of 44.13
TeraGauss, relativistic corrections must be incorporated when computing this
cross section. This paper presents formalism for the QED magnetic Compton
differential cross section valid for both subcritical and supercritical fields,
yet restricted to scattered photons that are below pair creation threshold.
Calculations are developed for the particular case of photons initially
propagating along the field, mathematically simple specializations that are
germane to interactions involving relativistic electrons frequently found in
neutron star magnetospheres. This exposition of relativistic, quantum, magnetic
Compton cross sections treats electron spin dependence fully, since this is a
critical feature for describing the finite decay lifetimes of the intermediate
states. The formalism employs both the Johnson and Lippmann (JL) wave functions
and the Sokolov and Ternov (ST) electron eigenfunctions of the magnetic Dirac
equation. The ST states are formally correct for self-consistently treating
spin-dependent effects that are so important in the resonances. Relatively
compact analytic forms for the cross sections are presented that will prove
useful for astrophysical modelers.Comment: 45 pages, 10 figures, accepted for publication in Phys. Rev.
Reconciling transport models across scales: the role of volume exclusion
Diffusive transport is a universal phenomenon, throughout both biological and
physical sciences, and models of diffusion are routinely used to interrogate
diffusion-driven processes. However, most models neglect to take into account
the role of volume exclusion, which can significantly alter diffusive
transport, particularly within biological systems where the diffusing particles
might occupy a significant fraction of the available space. In this work we use
a random walk approach to provide a means to reconcile models that incorporate
crowding effects on different spatial scales. Our work demonstrates that
coarse-grained models incorporating simplified descriptions of excluded volume
can be used in many circumstances, but that care must be taken in pushing the
coarse-graining process too far
SPIRAL Phase A: A Prototype Integral Field Spectrograph for the AAT
We present details of a prototype fiber feed for use on the Anglo-Australian
Telescope (AAT) that uses a dedicated fiber-fed medium/high resolution (R >
10000) visible-band spectrograph to give integral field spectroscopy (IFS) of
an extended object. A focal reducer couples light from the telescope to the
close-packed lenslet array and fiber feed, allowing the spectrograph be used on
other telescopes with the change of a single lens. By considering the
properties of the fibers in the design of the spectrograph, an efficient design
can be realised, and we present the first scientific results of a prototype
spectrograph using a fiber feed with 37 spatial elements, namely the detection
of Lithium confirming a brown dwarf candidate and IFS of the supernova remnant
SN1987A.Comment: 41 pages, 15 figures, 3 tables; accepted by PAS
Suppression of allergic airway inflammation by helminth-induced regulatory T cells
Allergic diseases mediated by T helper type (Th) 2 cell immune responses are rising dramatically in most developed countries. Exaggerated Th2 cell reactivity could result, for example, from diminished exposure to Th1 cell–inducing microbial infections. Epidemiological studies, however, indicate that Th2 cell–stimulating helminth parasites may also counteract allergies, possibly by generating regulatory T cells which suppress both Th1 and Th2 arms of immunity. We therefore tested the ability of the Th2 cell–inducing gastrointestinal nematode Heligmosomoides polygyrus to influence experimentally induced airway allergy to ovalbumin and the house dust mite allergen Der p 1. Inflammatory cell infiltrates in the lung were suppressed in infected mice compared with uninfected controls. Suppression was reversed in mice treated with antibodies to CD25. Most notably, suppression was transferable with mesenteric lymph node cells (MLNC) from infected animals to uninfected sensitized mice, demonstrating that the effector phase was targeted. MLNC from infected animals contained elevated numbers of CD4(+)CD25(+)Foxp3(+) T cells, higher TGF-β expression, and produced strong interleukin (IL)-10 responses to parasite antigen. However, MLNC from IL-10–deficient animals transferred suppression to sensitized hosts, indicating that IL-10 is not the primary modulator of the allergic response. Suppression was associated with CD4(+) T cells from MLNC, with the CD4(+)CD25(+) marker defining the most active population. These data support the contention that helminth infections elicit a regulatory T cell population able to down-regulate allergen induced lung pathology in vivo
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