3,930 research outputs found
A ground track control algorithm for the Topographic Mapping Laser Altimeter (TMLA)
The results of an analysis of an algorithm that will provide autonomous onboard orbit control using orbits determined with Global Positioning System (GPS) data. The algorithm uses the GPS data to (1) compute the ground track error relative to a fixed longitude grid, and (2) determine the altitude adjustment required to correct the longitude error. A program was written on a personal computer (PC) to test the concept for numerous altitudes and values of solar flux using a simplified orbit model including only the J sub 2 zonal harmonic and simple orbit decay computations. The algorithm was then implemented in a precision orbit propagation program having a full range of perturbations. The analysis showed that, even with all perturbations (including actual time histories of solar flux variation), the algorithm could effectively control the spacecraft ground track and yield more than 99 percent Earth coverage in the time required to complete one coverage cycle on the fixed grid (220 to 230 days depending on altitude and overlap allowance)
Knowledge-Driven Contrast Gain Control is Characterized by Two Distinct Electrocortical Markers
Sensitivity to variations in luminance (contrast) is fundamental to perception because contrasts define the edges and textures of visual objects. Recent research has shown that contrast sensitivity, in addition to being controlled by purely stimulus-driven mechanisms, is also affected by expectations and prior knowledge about the contrast of upcoming stimuli. The ability to adjust contrast sensitivity based on expectations and prior knowledge could help to maximize the information extracted when scanning familiar visual scenes. In the present study we used the event-related potentials (ERP) technique to resolve the stages that mediate knowledge-driven aspects of contrast gain control. Using groupwise independent components analysis and multivariate partial least squares, we isolated two robust spatiotemporal patterns of electrical brain activity associated with preparation for upcoming targets whose contrast was predicted by a cue. The patterns were sensitive to the informative value of the cue. When the cues were informative, these patterns were also able to differentiate among cues that predicted low-contrast targets and cues that predicted high-contrast targets. Both patterns were localized to parts of occipitotemporal cortex, and their morphology, latency, and topography resembled P2/N2 and P3 potentials. These two patterns provide electrophysiological markers of knowledge-driven preparation for impending changes in contrast and shed new light on the manner in which top-down factors modulate sensory processing
LCDG4 and DigiSim - Simulation activities at NICADD/NIU
We present two software packages developed to support detector R&D studies
for the International Linear Collider. LCDG4 is a full-detector simulator that
provides energy deposits from particles traversing the sensitive volumes of the
detector. It has been extensively used within the American ILC community,
providing data for algorithm development and detector optimization studies.
DigiSim models real-life digitization effects, converting the idealized
response into simulated detector readout. It has many useful features to
improve the realism in modeling detector response. The main characteristics of
these two complementary packages are discussed.Comment: 8 pages, 7 figures, submitted to LCWS05 conference proceedings. Uses
slac_one.rt
Empirical Solar Wind Forecasting from the Chromosphere
Recently, we correlated the inferred structure of the solar chromospheric
plasma topography with solar wind velocity and composition data measured at
1AU. We now offer a physical justification of these relationships and present
initial results of a empirical prediction model based on them. While still
limited by the fundamentally complex physics behind the origins of the solar
wind and how its structure develops in the magnetic photosphere and expands
into the heliosphere, our model provides a near continuous range of solar wind
speeds and composition quantities that are simply estimated from the inferred
structure of the chromosphere. We suggest that the derived quantities may
provide input to other, more sophisticated, prediction tools or models such as
those to study Coronal Mass Ejections (CME) propagation and Solar Energetic
Particle (SEP) generation.Comment: In Press ApJ [March 2007] - 14 pages, 4 figures, one movie [available
on request
Temporary inhibition of Moloney-murine sarcoma virus (M-MSV) induced-tumours by adoptive transfer of ricin-treated T-lymphocytes.
The potential use of tumour-specific T-lymphocytes loaded with ricin in cell targeting experiments was investigated. Moloney-murine sarcoma virus (M-MSV)-specific T-lymphocytes, obtained in mass mixed leucocyte-tumour cell culture (MLTC) and a M-MSV-specific cytotoxic T-lymphocyte (CTL) clone, were incubated with 125I-labelled ricin in order to evaluate toxin uptake and release. The internalized ricin (4.5 X 10(-17) mol and 6.5 X 10(-17) mol per 10(2) MLTC and CTL clone cells, respectively) was released rapidly during the first 30 min following treatment, and at a constant but slower rate over the next few hours. The cytotoxic activity of ricin-treated cells evaluated against antigen-related target cells, in a short term incubation 51Cr release assay, was unaffected during the first 30 min after treatment but decreased with time over the next few hours. However, the growth of antigen related as well as of unrelated tumour cells was strongly inhibited by the addition of ricin-treated cells to the culture system, thus indicating that released ricin is toxic for untreated target cells. The in vivo localization pattern of ricin-treated radiolabelled MLTC cells was found to be comparable with that of untreated cells 1 h after i.v. injection into syngeneic sublethally irradiated mice. After 6 h, however, more radiolabel was recovered from the liver of mice receiving ricin-treated MLTC cells. Ricin-treated M-MSV-specific T-lymphocytes were injected i.v. into tumour bearing sublethally irradiated mice. A temporary tumour growth inhibition (up to 6 days) was achieved following transfer of low doses of ricin-treated MLTC or CTL clone cells (1 X 10(6) and 0.5 X 10(6), respectively). In contrast, in M-MSV injected control mice, receiving only free toxin (from 5 to 20 ng) or untreated tumour-specific effector cell tumours grew progressively. The therapeutic effect was apparently specific since the injection of ricin-treated alloreactive T-lymphocytes did not influence tumour growth. These results suggest that M-MSV-specific T-lymphocytes loaded with ricin can deliver toxin to the target tumour mass and have a transient therapeutic effect
Spatiotemporal Dependency of Age-Related Changes in Brain Signal Variability
Recent theoretical and empirical work has focused on the variability of network dynamics in maturation. Such variability seems to reflect the spontaneous formation and dissolution of different functional networks. We sought to extend these observations into healthy aging. Two different data sets, one EEG (total n = 48, ages 18-72) and one magnetoencephalography (n = 31, ages 20-75) were analyzed for such spatiotemporal dependency using multiscale entropy (MSE) from regional brain sources. In both data sets, the changes in MSE were timescale dependent, with higher entropy at fine scales and lower at more coarse scales with greater age. The signals were parsed further into local entropy, related to information processed within a regional source, and distributed entropy (information shared between two sources, i.e., functional connectivity). Local entropy increased for most regions, whereas the dominant change in distributed entropy was age-related reductions across hemispheres. These data further the understanding of changes in brain signal variability across the lifespan, suggesting an inverted U-shaped curve, but with an important qualifier. Unlike earlier in maturation, where the changes are more widespread, changes in adulthood show strong spatiotemporal dependenc
LCDG4 and DigiSim – Simulation activities at NICADD/NIU
We present two software packages developed to support detector R&D studies for the International Linear Collider.
LCDG4 is a full-detector simulator that provides energy deposits from particles traversing the sensitive volumes of the
detector. It has been extensively used within the American ILC community, providing data for algorithm development
and detector optimization studies. DigiSim models real-life digitization effects, converting the idealized response into
simulated detector readout. It has many useful features to improve the realism in modeling detector response. The
main characteristics of these two complementary packages are discussed
Evolution of optically faint AGN from COMBO-17 and GEMS
We have mapped the AGN luminosity function and its evolution between z=1 and
z=5 down to apparent magnitudes of . Within the GEMS project we have
analysed HST-ACS images of many AGN in the Extended Chandra Deep Field South,
enabling us to assess the evolution of AGN host galaxy properties with cosmic
time.Comment: to appear in proceedings 'Multiwavelength AGN Surveys', Cozumel 200
Extended matrix Gelfand-Dickey hierarchies: reduction to classical Lie algebras
The Drinfeld-Sokolov reduction method has been used to associate with
extensions of the matrix r-KdV system. Reductions of these systems to the fixed
point sets of involutive Poisson maps, implementing reduction of to
classical Lie algebras of type , are here presented. Modifications
corresponding, in the first place to factorisation of the Lax operator, and
then to Wakimoto realisations of the current algebra components of the
factorisation, are also described.Comment: plain TeX, 12 page
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