The diffraction of waves by slits and strips
Plane wave diffraction by infinite strips and slitted planes, obtaining asymptotic expansions valid for HF
Wolfe, P.↗
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Annular slit colloid thruster research and development
Research in optimization of performance, and performance characteristics of annular slit colloid thruster
Burton, W. A.↗
Single stage evaluation of highly loaded high Mach number compressor stages. 4: Data and performance of hub slit suction stator
Performance tests and efficiency measurement of hub-slit-suction stator in single stage compressor
Burger, G. D.↗
Cancellation of slit-width and doppler broadening effects in the spectroscopy of fast ion beams
Spectrometer slit-width cancellation by Doppler shift of light emission by fast ion beams, resulting in spectral lines increased intensities
Leavitt, J. A.↗
A tool for cutting ultra thin slits in metals
Tool produces slits of 0.0305 mm widths in materials up to RC 50 hardness, minimizes material waste and improves precision. Device may be used for general metal cutting and for producing simulated cracks in metal samples used in fatigue tests.
Mcmahon, W.↗
Two-phase choked flow of subcooled nitrogen through a slit
Two-phase choked flow rate and pressure distribution data are reported for subcooled nitrogen flowing through a slit. The slip was a narrow rectangular passage of equal length and width. The inlet stagnation pressure ranged from slightly above saturation to twice the thermodynamic critical pressure. Four stagnation isotherms were investigated covering a range which spanned the critical temperature. The results suggested a uniform two-phase flow pattern with vaporization occurring at or near the exit in most cases. The results compared favorably with the theory of Henry for nonequilibrium subcooled two-phase choked flow in long tubes.
Simoneau, R. J.↗
Process for manufacturing slit collimators
Peculiarities are described of the manufacturing process and the control of elements of slit collimators, the structural design of the required equipment and the process or assembling the collimators.
Romanenko, V. P.↗
The scattering of electromagnetic pulses by a slit in a conducting screen
A direct method for calculating the impulse response of a slit in a conducting screen is presented which is derived specifically for the analysis of transient scattering by two-dimensional objects illuminated by a plane incident wave. The impulse response is obtained by assuming that the total response is composed of two sequences of diffracted waves. The solution is determined for the first two waves in one sequence by using Green's functions and the equivalence principle, for additional waves in the sequence by iteration, and for the other sequence by a transformation of coordinates. The cases of E-polarization and H-polarization are considered.
Ackerknecht, W. E., III↗
Parameter estimation for slit-type scanning sensors
The Infrared Astronomical Satellite, scheduled for launch into a 900 km near-polar orbit in August 1982, will perform an infrared point source survey by scanning the sky with slit-type sensors. The description of position information is shown to require the use of a non-Gaussian random variable. Methods are described for deciding whether separate detections stem from a single common source, and a formulism is developed for the scan-to-scan problems of identifying multiple sightings of inertially fixed point sources for combining their individual measurements into a refined estimate. Several cases are given where the general theory yields results which are quite different from the corresponding Gaussian applications, showing that argument by Gaussian analogy would lead to error.
Fowler, J. W.↗
Solid particle impingement erosion characteristics of cylindrical surfaces, pre-existing holes and slits
The erosion characteristics of aluminum cylinders sand-blasted with both spherical and angular erodent particles were studied and compared with results from previously studied flat surfaces. The cylindrical results are discussed with respect to impact conditions. The relationship between erosion rate and pit morphology (width, depth, and width to depth ratio) is established. The aspects of (1) erosion rate versus time curves on cylindrical surfaces; (2) long-term exposures; and (3) erosion rate versus time curves with spherical and angular particles are presented. The erosion morphology and characteristics of aluminum surfaces with pre-existing circular cylindrical and conical holes of different sizes were examined using weight loss measurements, scanning electron microscopy, a profilometer, and a depth gage. The morphological features (radial and concentric rings) are discussed with reference to flat surfaces, and the erosion features with spherical microglass beads. The similarities and differences of erosion and morphological features are highlighted. The erosion versus time curves of various shapes of holes are discussed and are compared with those of a flat surface. The erosion process at slits is considered.
Rao, P. V.↗
Modulated Multiple Slit Camera for improved localization of gamma ray bursts
An instrument is described in which a cylindrical modulation collimator is added to one half of a Multiple Slit Camera (MSC) coded-aperture imaging system. The instrument provides gamma-ray burst positions from a single spacecraft that are as precise as the best positions from the long-baseline network of interplanetary spacecraft. The determination of fine positions is described, and the fine-position capability is shown to operate over about two-thirds of the MSC's nearly all-sky field of view. It is noted that the addition of the modulation collimator only slightly reduces the system's sensitivity and can improve the location precision for gamma-ray bursts and slower hard-X-ray transients to about 0.1 sq arcmin.
Gorenstein, P.↗
Long-slit spectroscopy of gas in the cores of X-ray luminous clusters
The results of long-slit spectroscopy obtained for the core regions of 14 clusters of galaxies are reported. The data are presented in detail. It is shown that the presence of optical emission is tied to the properties of the hot gas in the cluster and not to the morphology of the central galaxy or cluster, demonstrating that the optical systems are indeed formed by the cooling of hot gas. Cooling flows occur when the gas density exceeds a critical central value which corresponds to a cooling time scale which, it is argued, weakly favors low values of H(0). The kinematics of the gas flows are discussed. The excitation mechanisms, correlation of optical emission with radio properties, and upper limits on coronal line strengths from the hot gas are discussed.
Hu, E. M.↗
A faint-object grism spectrograph with multiple slits and CCD detector
A high-efficiency spectrograph for research on faint astronomical objects has been successfully built and is in regular use on the Multiple-Mirror Telescope (MMT). It is equipped with a motorized multi-slit mechanism to allow simultaneous observations of several objects. The combination of high throughput, multiple object capability, and low-noise CCD detector has allowed routine work to be extended to objects of V magnitude 23 and fainter.
Geary, John C.↗
Wavelength-precise slit spectroscopy with optical fiber image scramblers
The application of optical-fiber image scramblers in wavelength-precise slit spectroscopy is discussed together with the design strategy for the optimal instrument configuration incorporating an optical-fiber image scrambler. Particular attention is given to the aspects of data analysis and interpretation techniques which must be specially designed for high-precision spectroscopy. In a specific application to an existing coude spectrograph, the instrumentation and data reduction techniques described in this paper demonstrate an achievable precision corresponding to a systematic radial velocity error of about 30 m/sec.
Heacox, William D.↗
Numerical simulation of rarefied gas flow through a slit
Two different approaches, the finite-difference method coupled with the discrete-ordinate method (FDDO), and the direct-simulation Monte Carlo (DSMC) method, are used in the analysis of the flow of a rarefied gas from one reservoir to another through a two-dimensional slit. The cases considered are for hard vacuum downstream pressure, finite pressure ratios, and isobaric pressure with thermal diffusion, which are not well established in spite of the simplicity of the flow field. In the FDDO analysis, by employing the discrete-ordinate method, the Boltzmann equation simplified by a model collision integral is transformed to a set of partial differential equations which are continuous in physical space but are point functions in molecular velocity space. The set of partial differential equations are solved by means of a finite-difference approximation. In the DSMC analysis, three kinds of collision sampling techniques, the time counter (TC) method, the null collision (NC) method, and the no time counter (NTC) method, are used.
Keith, Theo G., Jr.↗
Long slit spectroscopy of NGC 5506
The galaxy NGC 5506 hosts an active nucleus, that presents characteristics that are intermediate between Sy1 and Sy2. We discuss long slit spectra of NGC 5506 in the ranges 4675-5475 A and 6300-7125 A, that were obtained at three different position angles, in Apr. 1991 at the WHT 4.2 m telescope. The peculiar kinematics of the emitting gas has already been observed by other researchers; following the model proposed by the other researchers, that the emitting gas is located in two cones, we determined the aperture of the cones. The data, moreover, support the hypothesis that the gas is receding from the nucleus. We modelled the intensity and the ratios of the emission lines, and verified that the active nucleus of NGC 5506 can be described as a Sy1 nucleus, with the UV-X source that is partially obscured to our line of sight. On the contrary, a good fraction of the interstellar gas of the galaxy is directly illuminated and photoionized by the central source. Our data show evidence of star formation close to the nucleus; we estimated the star formation rate, that is high with respect to 'normal' spirals, but not high enough to be comparable to star formation rates in a starburst galaxy.
Stanga, R. M.↗
Numerical simulation of rarefied flow through a slit. I - Direct simulation Monte Carlo results
The pressure-driven flow of a rarefied monatomic gas through a two-dimensional slit is simulated using the direct simulation Monte Carlo technique. Of particular interest is the change in flow field structure as pressure ratio and Knudsen number are varied. Comparisons are made to quantify the limits of validity of free-molecular theory and approximate, nearly free-molecular iterative methods. Also addressed is the sensitivity of the numerical solutions to grid structure and boundary conditions. The free-molecular theory is found to predict quantitative flow field properties (e.g., centerline velocities or downstream flux profiles) reasonably well for large finite Knudsen number with the error dependent on the pressure ratio. The nearly free-molecular corrections are shown to have limited range of applicability. A previously derived parameter is found to correlate total mass flux well as a function of pressure ratio and Knudsen number over a large portion of the transitional regime.
Wadsworth, D. C.↗
Lick slit spectra of thirty-eight objective prism quasar candidates and low metallicity halo stars
Lick Observatory slit spectra of 38 objects which were claimed to have pronounced UV excess and emission lines are presented. Eleven QSOs, four galaxies at z of about 0.1, 22 stars, and one unidentified object with a low S/N spectrum were found. Of 11 objects which Zhan and Chen (1987, 1989) suggested were QSO with z(prism) not greater than 2.8; eight are QSOs. Six of the QSOs show absorption systems, including Q0000+027A with a relatively strong associated C IV absorption system, and Q0008+008 with a damped Ly-alpha system with an H I column density of 10 exp 21/sq cm. The equivalent widths of the Ca II K line, the G band, and the Balmer lines in 10 stars with the best spectra are measured, and metallicities are derived. Seven of them are in the range -2.5 to -1.7, while the others are less metal-poor.
Tytler, David↗