1,193 research outputs found
Development of a drive system for a sequential space camera
An electronically commutated dc motor is reported for driving the camera claw and magazine, and a stepper motor is described for driving the shutter with the two motors synchronized electrically. Subsequent tests on the breadboard positively proved the concept, but further development beyond this study should be done. The breadboard testing also established that the electronically commutated motor can control speed over a wide dynamic range, and has a high torque capability for accelerating loads. This performance suggested the possibility of eliminating the clutch from the system while retaining all of the other mechanical features of the DAC, if the requirement for independent shutter speeds and frame rates can be removed. Therefore, as a final step in the study, the breadboard shutter and shutter drive were returned to the original DAC configuration, while retaining the brushless dc motor drive
Development of a drive system for a sequential space camera
Breadboard models of single and dual motor drives for the shutter, claw and magazine of a space camera system were designed and tested. The single motor technique utilizes a single electronically commutated motor to drive the claw and shutter without resorting to a solenoid actuated clutch for pulse operation. Shutter speed is established by a combination of the cinemode speed and the opening of the conventional DAC two piece shutter. Pulse mode operation is obtained by applying power at a fixed clock rate and removing power at an appropriate point in the mechanical cycle such that the motor comes to rest by system friction. The dual motor approach utilizes a stepper motor to drive the shutter and an electronically commutated dc motor to drive the claw and magazine functions. The motors are synchronized electronically
Development of a drive system for a sequential space camera contract modification 4(S)
The brush type dc motor and clutch were eliminated from the design of the 16 mm space sequential camera design and replaced by an electronically commutated motor. The new drive system reduces the current consumption at 24 fps to 220 mA. The drive can be programmed and controlled externally from the multipurpose programmable timer/intervalometer, as well as being controlled locally from the camera
Automatic exposure control for space sequential camera
The final report for the automatic exposure control study for space sequential cameras, for the NASA Johnson Space Center is presented. The material is shown in the same sequence that the work was performed. The purpose of the automatic exposure control is to automatically control the lens iris as well as the camera shutter so that the subject is properly exposed on the film. A study of design approaches is presented. Analysis of the light range of the spectrum covered indicates that the practical range would be from approximately 20 to 6,000 foot-lamberts, or about nine f-stops. Observation of film available from space flights shows that optimum scene illumination is apparently not present in vehicle interior photography as well as in vehicle-to-vehicle situations. The evaluation test procedure for a breadboard, and the results, which provided information for the design of a brassboard are given
Automatic Exposure Iris Control (AEIC) for data acquisition camera
A lens design capable of operating over a total range of f/1.4 to f/11.0 with through the lens light sensing is presented along with a system which compensates for ASA film speeds as well as shutter openings. The space shuttle camera system package is designed so that it can be assembled on the existing 16 mm DAC with a minimum of alteration to the camera
Neutron imaging and modelling inclined vortex driven thin films.
The vortex fluidic device (VFD) is a thin film microfluidic platform which has a wide range of applications in synthesis and other areas of science, and it is important to understand the nature of the thin film of liquid in its inclined rapidly rotating tube. Neutron imaging has been used to determine the thickness of the film in a quartz tube with its shape modelled mathematically, showing good agreement between the model and experiments. The resultant equations are useful for studying VFD mediated processing in general, for which the optimal tilt angle of the tube is typically 45°. This includes its utility for the intelligent scale-up of organic syntheses, as demonstrated in the present study by the scaling up of an imine and amide synthesis to >1âg/min
On the possible existence of short-period g-mode instabilities powered by nuclear burning shells in post-AGB H-deficient (PG1159-type) stars
We present a pulsational stability analysis of hot post-AGB H-deficient
pre-white dwarf stars with active He-burning shells. The stellar models
employed are state-of-the-art equilibrium structures representative of PG1159
stars derived from the complete evolution of the progenitor stars. On the basis
of fully nonadiabatic pulsation computations, we confirmed theoretical evidence
for the existence of a separate PG1159 instability strip in the diagram characterized by short-period -modes excited by the
-mechanism. This instability strip partially overlaps the already
known GW Vir instability strip of intermediate/long period -modes
destabilized by the classical -mechanism acting on the partial
ionization of C and/or O in the envelope of PG1159 stars. We found that PG1159
stars characterized by thick He-rich envelopes and located inside this
overlapping region could exhibit both short and intermediate/long periods
simultaneously. we study the particular case of VV 47, a pulsating planetary
nebula nucleus that has been reported to exhibit a series of unusually short
pulsation periods. We found that the long periods exhibited by VV 47 can be
readily explained by the classical -mechanism, while the observed
short-period branch below s could correspond to modes triggered
by the He-burning shell through the -mechanism, although more
observational work is needed to confirm the reality of these short-period
modes. Were the existence of short-period -modes in this star convincingly
confirmed by future observations, VV 47 could be the first known pulsating star
in which both the -mechanism and the -mechanism of mode
driving are simultaneously operating.Comment: 9 pages, 5 figures, 2 tables. To be published in The Astrophysical
Journa
Anodic dissolution of metals in oxide-free cryolite melts
The anodic behavior of metals in molten cryolite-alumina melts has been investigated mostly for use as inert anodes for the Hall-HĂ©roult process. In the present work, gold, platinum, palladium, copper, tungsten, nickel, cobalt and iron metal electrodes were anodically polarized in an oxide-free cryolite melt (11%wt. excess AlF3 ; 5%wt. CaF2) at 1273 K. The aim of the experiments was to characterize the oxidation reactions of the metals occurring without the effect of oxygen-containing dissolved species. The anodic dissolution of each metal was demonstrated, and electrochemical reactions were assigned using reversible potential calculation. The relative stability of metals as well as the possibility of generating pure fluorine is discussed
Modeling Dyslexic Studentsâ Motivation for Enhanced Learning in E-learning Systems
E-Learning systems can support real-time monitoring of learnersâ learning desires and effects, thus offering opportunities for enhanced personalized learning. Recognition of the determinants of dyslexic usersâ motivation to use e-learning systems is important to help developers improve the design of e-learning systems and educators direct their efforts to relevant factors to enhance dyslexic studentsâ motivation. Existing research has rarely attempted to model dyslexic usersâ motivation in e-learning context from a comprehensive perspective. The present work has conceived a hybrid approach, namely, combining the strengths of qualitative and quantitative analysis methods, to motivation modeling. It examines a variety of factors that affect dyslexic studentsâ motivation to engage in e-learning systems from psychological, behavioral, and technical perspectives, and establishes their interrelationships. Specifically, the study collects data from a multi-item
Likert-style questionnaire to measure relevant factors for conceptual motivation modeling. It then applies both covariance-based (CB-SEM) and variance-based structural equation modeling (PLS-SEM) approaches to
determine the quantitative mapping between dyslexic studentsâ continued use intention and motivational factors, followed by discussions about theoretical findings and design instructions according to our motivation model. Our research has led to a novel motivation model with new constructs of Learning Experience, Reading Experience, Perceived Control, and Perceived Privacy. From both the CB-SEM and PLS-SEM analyses, results on the total effects have indicated consistently that Visual Attractiveness, Reading Experience, and Feedback have the strongest effects on continued use intentio
First Attempt at Spectroscopic Detection of Gravity Modes in a Long-Period Pulsating Subdwarf B Star -- PG 1627+017
In the first spectroscopic campaign for a PG 1716 variable (or long-period
pulsating subdwarf B star), we succeeded in detecting velocity variations due
to g-mode pulsations at a level of 1.0-1.5 km/s.The observations were obtained
during 40 nights on 2-m class telescopes in Arizona, South Africa,and
Australia. The target,PG1627+017, is one of the brightest and largest amplitude
stars in its class.It is also the visible component of a post-common envelope
binary.Our final radial velocity data set includes 84 hours of time-series
spectroscopy over a time baseline of 53 days. Our derived radial velocity
amplitude spectrum, after subtracting the orbital motion, shows three potential
pulsational modes 3-4 sigma above the mean noise level, at 7201.0s,7014.6s and
7037.3s.Only one of the features is statistically likely to be real,but all
three are tantalizingly close to, or a one day alias of, the three strongest
periodicities found in the concurrent photometric campaign. We further
attempted to detect pulsational variations in the Balmer line amplitudes. The
single detected periodicity of 7209 s, although weak, is consistent with
theoretical expectations as a function of wavelength.Furthermore, it allows us
to rule out a degree index of l= 3 or l= 5 for that mode. Given the extreme
weakness of g-mode pulsations in these stars,we conclude that anything beyond
simply detecting their presence will require larger telescopes,higher
efficiency spectral monitoring over longer time baselines,improved longitude
coverage, and increased radial velocity precision.Comment: 39 pages, 9 figures, 4 tables, ApJ accepted. See postscript for full
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