7,155 research outputs found
NASA ground terminal communication equipment automated fault isolation expert systems
The prototype expert systems are described that diagnose the Distribution and Switching System I and II (DSS1 and DSS2), Statistical Multiplexers (SM), and Multiplexer and Demultiplexer systems (MDM) at the NASA Ground Terminal (NGT). A system level fault isolation expert system monitors the activities of a selected data stream, verifies that the fault exists in the NGT and identifies the faulty equipment. Equipment level fault isolation expert systems are invoked to isolate the fault to a Line Replaceable Unit (LRU) level. Input and sometimes output data stream activities for the equipment are available. The system level fault isolation expert system compares the equipment input and output status for a data stream and performs loopback tests (if necessary) to isolate the faulty equipment. The equipment level fault isolation system utilizes the process of elimination and/or the maintenance personnel's fault isolation experience stored in its knowledge base. The DSS1, DSS2 and SM fault isolation systems, using the knowledge of the current equipment configuration and the equipment circuitry issues a set of test connections according to the predefined rules. The faulty component or board can be identified by the expert system by analyzing the test results. The MDM fault isolation system correlates the failure symptoms with the faulty component based on maintenance personnel experience. The faulty component can be determined by knowing the failure symptoms. The DSS1, DSS2, SM, and MDM equipment simulators are implemented in PASCAL. The DSS1 fault isolation expert system was converted to C language from VP-Expert and integrated into the NGT automation software for offline switch diagnoses. Potentially, the NGT fault isolation algorithms can be used for the DSS1, SM, amd MDM located at Goddard Space Flight Center (GSFC)
Commissioning of the GEM-CSC Integrated Local Trigger for Run-3 of the CMS Experiment at the Large Hadron Collider
The high luminosity upgrade to the Large Hadron Collider (LHC), means a significant increase in data, which the existing muon trigger system’s bandwidth is inadequate to process. The solution for enabling the muon system to handle this increase in data is the installation of thin Gas Electron Multiplier (GEM) detectors in front of the existing Cathode Strip Chambers (CSC), where the magnetic field is strong allowing for best measurement of the transverse momentum (p). By combining the data from the new GE1/1 system with the ME1/1, we can increase the p resolution of the Level one (L1) trigger, allowing us to filter out many soft muons which otherwise would have been incorrectly reconstructed by the ME1/1 system alone, thus reducing the load on the higher level triggering system to catch these poor quality muons. In order to successfully implement this combined triggering system in time for the scheduled run-3, there must be an efficient means of commission the combined trigger system. This thesis describes the software and hardware developed to verify proper operation of this combined triggering system. This will vastly speed up the process of commissioning the combined Integrated Local Trigger (ILT), which will reduce the time wasted during installation, optimizing the amount of useful data collected by the CMS experiment
Characterization of photomultiplier tubes in a novel operation mode for Secondary Emission Ionization Calorimetry
Hamamatsu single anode R7761 and multi-anode R5900-00-M16 Photomultiplier
Tubes have been characterized for use in a Secondary Emission (SE) Ionization
Calorimetry study. SE Ionization Calorimetry is a novel technique to measure
electromagnetic shower particles in extreme radiation environments. The
different operation modes used in these tests were developed by modifying the
conventional PMT bias circuit. These modifications were simple changes to the
arrangement of the voltage dividers of the baseboard circuits. The PMTs with
modified bases, referred to as operating in SE mode, are used as an SE detector
module in an SE calorimeter prototype, and placed between absorber materials
(Fe, Cu, Pb, W, etc.). Here, the technical design of different operation modes,
as well as the characterization measurements of both SE modes and the
conventional PMT mode are reported
The origin of ultra diffuse galaxies: stellar feedback and quenching
We test if the cosmological zoom-in simulations of isolated galaxies from the
FIRE project reproduce the properties of ultra diffuse galaxies. We show that
stellar feedback-generated outflows that dynamically heat galactic stars,
together with a passively aging stellar population after imposed quenching
(from e.g. infall into a galaxy cluster), naturally reproduce the observed
population of red UDGs, without the need for high spin halos or dynamical
influence from their host cluster. We reproduce the range of surface
brightness, radius and absolute magnitude of the observed z=0 red UDGs by
quenching simulated galaxies at a range of different times. They represent a
mostly uniform population of dark matter-dominated galaxies with M_star ~1e8
Msun, low metallicity and a broad range of ages. The most massive simulated
UDGs require earliest quenching and are therefore the oldest. Our simulations
provide a good match to the central enclosed masses and the velocity
dispersions of the observed UDGs (20-50 km/s). The enclosed masses of the
simulated UDGs remain largely fixed across a broad range of quenching times
because the central regions of their dark matter halos complete their growth
early. A typical UDG forms in a dwarf halo mass range of Mh~4e10-1e11 Msun. The
most massive red UDG in our sample requires quenching at z~3 when its halo
reached Mh ~ 1e11 Msun. If it, instead, continues growing in the field, by z=0
its halo mass reaches > 5e11 Msun, comparable to the halo of an L* galaxy. If
our simulated dwarfs are not quenched, they evolve into bluer low-surface
brightness galaxies with mass-to-light ratios similar to observed field dwarfs.
While our simulation sample covers a limited range of formation histories and
halo masses, we predict that UDG is a common, and perhaps even dominant, galaxy
type around Ms~1e8 Msun, both in the field and in clusters.Comment: 20 pages, 13 figures; match the MNRAS accepted versio
Breathing FIRE: How Stellar Feedback Drives Radial Migration, Rapid Size Fluctuations, and Population Gradients in Low-Mass Galaxies
We examine the effects of stellar feedback and bursty star formation on
low-mass galaxies ()
using the FIRE (Feedback in Realistic Environments) simulations. While previous
studies emphasized the impact of feedback on dark matter profiles, we
investigate the impact on the stellar component: kinematics, radial migration,
size evolution, and population gradients. Feedback-driven outflows/inflows
drive significant radial stellar migration over both short and long timescales
via two processes: (1) outflowing/infalling gas can remain star-forming,
producing young stars that migrate within their first , and (2) gas outflows/inflows drive strong fluctuations in the
global potential, transferring energy to all stars. These processes produce
several dramatic effects. First, galaxies' effective radii can fluctuate by
factors of over , and these rapid size fluctuations
can account for much of the observed scatter in radius at fixed
Second, the cumulative effects of many outflow/infall episodes steadily heat
stellar orbits, causing old stars to migrate outward most strongly. This
age-dependent radial migration mixes---and even inverts---intrinsic age and
metallicity gradients. Thus, the galactic-archaeology approach of calculating
radial star-formation histories from stellar populations at can be
severely biased. These effects are strongest at , the same regime where feedback most
efficiently cores galaxies. Thus, detailed measurements of stellar kinematics
in low-mass galaxies can strongly constrain feedback models and test baryonic
solutions to small-scale problems in CDM.Comment: Accepted to ApJ (820, 131) with minor revisions from v1. Figure 4 now
includes dark matter. Main results in Figures 7 and 1
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