360 research outputs found
Numerical Integration Through Concavity Analysis
We introduce a relationship between the concavity of a C2 func- tion and the area bounded by its graph and secant line. We utilize this relationship to develop a method of numerical integration. We then bound the error of the approximation, and compare to known methods, finding an improvement in error bound over methods of comparable computational complexity
Independent Orbiter Assessment (IOA): Analysis of the DPS subsystem
The results of the Independent Orbiter Assessment (IOA) of the Failure Modes and Effects Analysis/Critical Items List (FMEA/CIL) is presented. The IOA approach features a top-down analysis of the hardware to independently determine failure modes, criticality, and potential critical items. The independent analysis results corresponding to the Orbiter Data Processing System (DPS) hardware are documented. The DPS hardware is required for performing critical functions of data acquisition, data manipulation, data display, and data transfer throughout the Orbiter. Specifically, the DPS hardware consists of the following components: Multiplexer/Demultiplexer (MDM); General Purpose Computer (GPC); Multifunction CRT Display System (MCDS); Data Buses and Data Bus Couplers (DBC); Data Bus Isolation Amplifiers (DBIA); Mass Memory Unit (MMU); and Engine Interface Unit (EIU). The IOA analysis process utilized available DPS hardware drawings and schematics for defining hardware assemblies, components, and hardware items. Each level of hardware was evaluated and analyzed for possible failure modes and effects. Criticality was assigned based upon the severity of the effect for each failure mode. Due to the extensive redundancy built into the DPS the number of critical items are few. Those identified resulted from premature operation and erroneous output of the GPCs
Independent Orbiter Assessment (IOA): Analysis of the guidance, navigation, and control subsystem
The results of the Independent Orbiter Assessment (IOA) of the Failure Modes and Effects Analysis (FMEA) and Critical Items List (CIL) is presented. The IOA approach features a top-down analysis of the hardware to determine failure modes, criticality, and potential critical items. To preserve independence, this analysis was accomplished without reliance upon the results contained within the NASA FMEA/CIL documentation. The independent analysis results corresponding to the Orbiter Guidance, Navigation, and Control (GNC) Subsystem hardware are documented. The function of the GNC hardware is to respond to guidance, navigation, and control software commands to effect vehicle control and to provide sensor and controller data to GNC software. Some of the GNC hardware for which failure modes analysis was performed includes: hand controllers; Rudder Pedal Transducer Assembly (RPTA); Speed Brake Thrust Controller (SBTC); Inertial Measurement Unit (IMU); Star Tracker (ST); Crew Optical Alignment Site (COAS); Air Data Transducer Assembly (ADTA); Rate Gyro Assemblies; Accelerometer Assembly (AA); Aerosurface Servo Amplifier (ASA); and Ascent Thrust Vector Control (ATVC). The IOA analysis process utilized available GNC hardware drawings, workbooks, specifications, schematics, and systems briefs for defining hardware assemblies, components, and circuits. Each hardware item was evaluated and analyzed for possible failure modes and effects. Criticality was assigned based upon the severity of the effect for each failure mode
A search for soft X-ray emission associated with prominent high-velocity-cloud complexes
We correlate the ROSAT 1/4 keV all-sky survey with the Leiden/Dwingeloo HI
survey, looking for soft X-ray signatures of prominent high-velocity-cloud
(HVC) complexes. We study the transfer of 1/4 keV photons through the
interstellar medium in order to distinguish variations in the soft X-ray
background (SXRB) intensity caused by photoelectric absorption effects from
those due to excess X-ray emission. The X-ray data are modelled as a
combination of emission from the Local Hot Bubble (LHB) and emission from a
distant plasma in the galactic halo and extragalactic sources. The X-ray
radiation intensity of the galactic halo and extragalactic X-ray background is
modulated by the photoelectric absorption of the intervening galactic
interstellar matter. We show that large- and small-scale intensity variations
of the 1/4 keV SXRB are caused by photoelectric absorption which is
predominantly traced by the total N(HI) distribution. The extensive coverage of
the two surveys supports evidence for a hot, X-ray emitting corona. We show
that this leads to a good representation of the SXRB observations. For four
large areas on the sky, we search for regions where the modelled and observed
X-ray emission differ. We find that there is excess X-ray emission towards
regions near HVC complexes C, D, and GCN. We suggest that the excess X-ray
emission is positionally correlated with the high-velocity clouds. Some lines
of sight towards HVCs also pass through significant amounts of
intermediate-velocity gas, so we cannot constrain the possible role played by
IVC gas in these directions of HVC and IVC overlap, in determining the X-ray
excesses.Comment: 16 pages, 8 figures, accepted for publication in Astronomy &
Astrophysics main journa
Superhumps of CC Cancri Revisited
We observed the 2001 November superoutburst of CC Cnc. This observation makes
the first detailed coverage of a superoutburst of this object. The
best-determined mean superhump period is 0.075518 +/- 0.000018 d, which is 2.7%
longer than the reported orbital period. This fractional superhump excess is a
quite typical value for a normal SU UMa-type dwarf nova, excluding the
previously raised possibility that CC Cnc may have an anomalously large
fractional superhump excess. During the superoutburst plateau, the object
showed a decrease of the superhump period at dot(P)/P = -10.2(1.3) x 10^(-5),
which is one of the largest negative period derivative known in all SU UMa-type
dwarf novae.Comment: 5 pages, 5 figures, to appear in Publ. Astron. Soc. Japa
Kilo-Second Quasi-Periodic Oscillations in the Cataclysmic Variable DW Cancri
Our photometric monitoring revealed that DW Cnc, which was originally
classified as a dwarf nova (V=15--17.5), remained at a bright state of
Rc=14.68+/-0.07 for 61 days. In conjunction with optical spectra lacking a
strong He II emission line, we propose that the object is not a dwarf nova, but
a non-magnetic nova-like variable. Throughout our monitoring, the object showed
strong quasi-periodic oscillations (QPOs) with amplitudes reaching about 0.3
mag. Our period analysis yielded a power spectrum with two peaks of QPOs, whose
center periods are 37.5+/-0.1 and 73.4+/-0.4 min and, furthermore, with a
significant power in frequencies lower than the QPOs. DW Cnc is a unique
cataclysmic variable in which kilo-second QPOs were continuously detected for
61 days. We propose two possible interpretations of DW Cnc: (i) A permanent
superhumper below the period minimum of hydrogen-rich cataclysmic variables.
(ii) A nova-like variable having an orbital period over 3 hours. In this case,
the QPOs may be caused by trapped disk oscillations.Comment: 6 pages, 4 figures, PASJ in pres
Photometric Observations of an SU UMa-type Dwarf Nova VW Coronae Borealis during Outbursts
We report the photometric observations of an SU UMa-type dwarf nova VW CrB
during two superoutbursts in 2001 and 2003 and a normal outburst in 2003.
Superhumps with a period of 0.07287(1) d were observed during the 2003
superoutburst. The change rate of the superhump period was positive. During the
normal outburst, there are some hint of modulation up to a 0.2-mag amplitude.
However, any periodicity was not found. The recurrence cycles of the normal
outburst and the superoutburst, and the distance were estimated to be > ~50 d,
270-500 d, and 690(+230, -170) pc, respectively. These recurrence cycles are
usual values for an SU UMa-type dwarf nova having this superhump period. The
superhump period of VW CrB was the longest among those of the SU UMa stars with
positive derivatives of the superhump period. The coverage of our observations
was, however, not enough, and the variation of the Psh change rate of VW CrB is
still unknown. A superhump regrowth and a brightening were seen near the end of
the plateau phase. Measuring the deviation of the start timings of the
brightening and the superhump regrowth (>2 days in VW CrB) will be a key to
reveal the mechanism of these phenomena.Comment: 7 pages, 8 figures, to appear in PAS
High Velocity Cloud Complex H: A Satellite of the Milky Way in a Retrograde Orbit?
Observations with the Green Bank Telescope of 21cm HI emission from the
high-velocity cloud Complex H suggest that it is interacting with the Milky
Way. A model in which the cloud is a satellite of the Galaxy in an inclined,
retrograde circular orbit reproduces both the cloud's average velocity and its
velocity gradient with latitude. The model places Complex H at approximately 33
kpc from the Galactic Center on a retrograde orbit inclined about 45 degrees to
the Galactic plane. At this location it has an HI mass > 6 10^6 Msun and
dimensions of at least 10 by 5 kpc. Some of the diffuse HI associated with the
cloud has apparently been decelerated by interaction with Galactic gas. Complex
H has similarities to the dwarf irregular galaxy Leo A and to some compact
high-velocity clouds, and has an internal structure nearly identical to parts
of the Magellanic Stream, with a pressure P/k about 100 cm^{-3} K.Comment: 12 pages includes 4 figures. To be published in Astrophysical Journal
Letters, 1 July 200
Parent based language intervention for 2-year-old children with specific expressive language delay: a randomised controlled trial
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