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Morris, D.

Publications and source records attributed to Morris, D..

33 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Progress towards the Facility for Rare Isotope Beams

Muon-based facilities offer a unique potential to provide capabilities at both the Intensity Frontier with Neutrino Factories and the Energy Frontier with Muon Colliders ranging from the Higgs energy to the multi-TeV energy range. They rely on novel technology with challenging parameters, for which the feasibility is currently being assessed by the U.S. Muon Accelerator Program (MAP) [1]. A realistic scenario for a complementary series of staged facilities with increasing complexity and significant physics potential at each stage has been developed. It takes advantage of and leverages the capabilities already planned at Fermilab, especially Project X and LBNE. Each stage is defined in such a way as to provide an R&D platform to validate the technologies required for subsequent stages. The rationale and sequence of a realistic staging process are presented.

Wei, J.↗
NASA NTRS1996

Optimization of Operations Resources via Discrete Event Simulation Modeling

The resource levels required for operation and support of reusable launch vehicles are typically defined through discrete event simulation modeling. Minimizing these resources constitutes an optimization problem involving discrete variables and simulation. Conventional approaches to solve such optimization problems involving integer valued decision variables are the pattern search and statistical methods. However, in a simulation environment that is characterized by search spaces of unknown topology and stochastic measures, these optimization approaches often prove inadequate. In this paper, we have explored the applicability of genetic algorithms to the simulation domain. Genetic algorithms provide a robust search strategy that does not require continuity and differentiability of the problem domain. The genetic algorithm successfully minimized the operation and support activities for a space vehicle, through a discrete event simulation model. The practical issues associated with simulation optimization, such as stochastic variables and constraints, were also taken into consideration.

Joshi, B.↗
NASA NTRS1995

CGRO-Comptel observations of the Centaurus A region

The sky region containing the active radio-galaxy Centaurus A has repeatedly been observed with the (COMPTEL) instrument onboard the Compton Gamma Ray Observatory (CGRO). The nine observation periods during the CGRO phases I and II in which Cen A was in the field of view of COMPTEL are spread over 18 months in the years 1991 to 1993. The energy range 0.75 to 30 MeV is covered. Clear evidence for a source with emission up to several MeV is seen from a region coinciding with the position of Cen A. The spectra change significantly over approximately 6 months between the two observation phases. A possible source confusion with the nearby gamma-ray source MS1312.1-4221 is discussed.

Steinle, H.↗
NASA NTRS1994

Diffuse continuum gamma rays from the Galaxy observed by COMPTEL

The diffuse Galactic continuum gamma-ray emission has been studied using the full Sky Survey from COMPTEL on the Compton Observatory CGRO. The diffuse emission appears to be visible in the whole 0.75-30 MeV range covered by the instrument, although a considerable contribution from unresolved point sources cannot be excluded. A correlation analysis using HI and CO surveys of the Galaxy is used to derive the Galactic emissivity spectrum, and this is consistent with a smooth continuation to the spectrum at higher energies derived by a similar analysis of COS-B data. The apparent conversion factor from integrated CO temperature to molecular hydrogen column density can also be determined from the correlation analysis. The value obtained is consistent with results from COS-B and other non-gamma-ray methods. Calculations of the emissivity spectrum from bremsstrahlung from a cosmic-ray electron spectrum based on propagation models are compared with the observations.

Strong, A. W.↗
NASA NTRS1994

COMPTEL upper limits on gamma-ray line emission from Supernova 1991T

The imaging Compton telescope COMPTEL on board the Compton Gamma-Ray Observatory (CGRO) measures gamma-rays in the energy range 0.75-30 MeV with an energy resolution of 9.7% full width at half maximum (FWHM) at 1 MeV. From June 15 to 28, 1991 and again from October 3 to 17, 1991 the region containing the supernova SN 1991T was observed. A search for gamma-ray line emission from the supernova yields no detection of line emission from the supernova. 2 sigma upper limits for the two predicted lines at 847 keV and at 1.238 MeV of approximately equal to 3 x 10(exp -5) photons/(sq cm)(s) were derived. These limits are compared with the predictions of some theoretical models and constraints imposed by these limits on these models are discussed.

Lichti, G. G.↗
NASA NTRS1994

Diffuse galactic continuum emission measured by COMPTEL and the cosmic-ray electron spectrum

Diffuse galactic continuum gamma-ray emission in the 0.75-30 MeV range from the inner Galaxy has been studied using data from COMPTEL on the Compton Gamma-Ray Observatory. Observations of the inner Galaxy from the Sky Survey have been used. The imaging properties of COMPTEL enable spatial analysis of the gamma-ray distribution using model fitting. A model based on atomic and molecular gas distributions in the Galaxy has been used to derive the emissivity spectrum of the gamma-ray emission and this spectrum is compared with theoretical estimates of bremsstrahlung emission from cosmic-ray electrons.

Strong, A. W.↗
NASA NTRS1994

COMPTEL observations of the 1.809 MeV gamma-ray line from galactic Al-26

The COMPTEL experiment on the Compton Gamma-Ray Observatory (CGRO) has been demonstrated to be capable of imaging the Galaxy within its field of view of about 1 steradian in the 1.809 MeV gamma-ray line originating from radioactive Al-26. The combined data from the CGRO sky survey in 1991/1992 have been analyzed to provide a first map of the inner Galaxy in this gamma-ray line. The 1.809 MeV emission appears extended along the inner 70 deg of the Galactic plane, with a relatively sharp falloff outside this regime. Correlations with massive stars and supernova remnants as possible tracers of the candidate Al-26 sources are discussed.

Diehl, R.↗
NASA NTRS1994

Hydrogen masers and cesium fountains at NRC

The NRC masers H-3 and H-4 have been operating since June 1993 with cavity servo control. These low-flux active H masers are showing stabilities of about 10(exp -15) from 1 hour to several days. Stability results are presented, and the current and planned uses of the masers are discussed. A cesium fountain primary frequency standard project has been started at NRC. Trapping and launching experiments with the goal of 7 m/s launches are beginning. We discuss our plans for a local oscillator and servo that exploit the pulsed aspect of cesium fountain standards, and meet the challenge of 10(exp -14) tau(exp -1/2) stability without requiring masers. At best, we expect to run this frequency standard initially for periods of hours each working day rather than continuously for years, and so frequency transfer to outside laboratories has been carefully considered. We conclude that masers (or other even better secondary clocks) are required to exploit this potential accuracy of the cesium fountain. We present and discuss our conclusion that it is feasible to transfer frequency in this way with a transfer-induced uncertainty of less than 10(exp -15), even in the presence of maser frequency drift and random walk noise.

Boulanger, J.-S.↗
NASA NTRS1994

COMPTEL observations of Ti-44 gamma-ray line emission from Cas A

The Compton Telescope (COMPTEL) telescope aboard the Compton Gamma-Ray Observatory (CGRO) is capable of imaging gamma-ray line sources in the MeV region with a sensitivity of the order 10(exp -5) photons/(sq cm s). During two observations periods in July 1992 and February 1993 the Galactic plane in the region of the young supernova remnant Cas A was observed, showing evidence for line emission at 1.16 MeV from the decay of Ti-44 at a significance level of approximately 4 sigma. This is the first time a supernova remnant has been detected in the gamma-ray line from Ti-44 decay. Adopting a distance of 2.8 kpc to the Cas A remnant, the measured line flux (7.0 +/- 1.7) x 10(exp -5) photons/(sq cm s), can be translated into a Ti-44 mass ejected during the Cas A supernova explosion, between (1.4 +/- 0.4) x 10(exp -4) solar mass and (3.2 +/- 0.8) x 10(exp -4) solar mass, depending on the precise value of the Ti-44 mean life time and on the precise date of the event. Implications of this result for supernova nucleosynthesis models are discussed.

Iyudin, A. F.↗
NASA NTRS1993

Time scale algorithms for an inhomogeneous group of atomic clocks

Through the past 17 years, the time scale requirements at the National Research Council (NRC) have been met by the unsteered output of its primary laboratory cesium clocks, supplemented by hydrogen masers when short-term stability better than 2 x 10(exp -12)tau(sup -1/2) has been required. NRC now operates three primary laboratory cesium clocks, three hydrogen masers, and two commercial cesium clocks. NRC has been using ensemble averages for internal purposes for the past several years, and has a realtime algorithm operating on the outputs of its high-resolution (2 x 10(exp -13) s at 1 s) phase comparators. The slow frequency drift of the hydrogen masers has presented difficulties in incorporating their short-term stability into the ensemble average, while retaining the long-term stability of the laboratory cesium frequency standards. We report on this work on algorithms for an inhomogeneous ensemble of atomic clocks, and on our initial work on time scale algorithms that could incorporate frequency calibrations at NRC from the next generation of Zacharias fountain cesium frequency standards having frequency accuracies that might surpass 10(exp -15), or from single-trapped-ion frequency standards (Ba+, Sr+,...) with even higher potential accuracies. The requirements for redundancy in all the elements (including the algorithms) of an inhomogeneous ensemble that would give a robust real-time output of the algorithms are presented and discussed.

Jacques, C.↗
NASA NTRS1993

The advanced cosmic microwave explorer - A millimeter-wave telescope and stabilized platform

We have developed and flown a 1 m diameter Gregorian telescope system for measurements of anisotropy in the Cosmic Background Radiation (CBR). The telescope is incorporated in a balloon-borne stabilized platform with arcminute stabilization capability. To date, the system has flown four times and observed from the ground at the South Pole twice. The telescope has used both coherent and incoherent detectors. We describe the development of the telescope, pointing platform, and one of the receivers employed in making measurements of the CBR. Performance of the system during the first flight and operation on the ground at the South Pole are described, and the quality of the South Pole as a millimeter wave observing site is discussed.

Meinhold, P. R.↗
NASA NTRS1992

Anisotropy in InGaAs/GaAs heterostructures grown by low-pressure MOVPE and CBE

InGaAs/GaAs heterostructures grown on (001) substrates by low-pressure MOVPE exhibit a measurable anisotropy in their structural, optical and electrical properties. This anisotropy occurs in structures which have undergone partial or complete strain relaxation and it can be strongly reduced by using slightly misoriented substrates. A comparison with similar structures grown by CBE indicates that this anisotropy is less important. This study suggests that strain relaxation is achieved by a combination of several mechanisms whose relative importance depends on the orientation of the substrate and on growth temperature which varies with the growth technique.

Roth, A. P.↗
NASA NTRS1986

ICE encounter operations

The operations encompassing the International Cometary Explorer's (ICE) encounter with the Comet Giacobini-Zinner on September 11, 1985 are documented. The ICE mission presented new challenges for the Deep Space Network (DSN) 64 meter subnetwork. Because of poor telemetry link margin predicted for Giacobini-Zinner (GZ) encounter, supplemental support by the Japanese Institute for Space and Astronautical Sciences 64-meter antenna at Usuda, Japan and the 305-meter Arecibo Radio Observatory in Puerto Rico was required. To improve the 64 meter subnetwork telemetry performance the following were also implemented: (1) Real time antenna array of 64 meter and 34 meter at a single complex and the required performance testing; and (2) Nonreal time antenna array of two complexes was implemented as a backup in the event of ground or spacecraft failure.

Fanelli, N.↗