Narrow Gaussian Research Articles

The Hβ line shape of Akn 120

We present here the Akn 120 H? line profiles from 97 spectra observed from 1977 till 1990 at Crimean Astrophysical Observatory (Appendix 1). The H? line has been fitted with three broad and one narrow Gaussian throughout the whole considered period. The central broad components of the H? and a shelf cause the H? line shape variation. Three broad Gaussians may suggest the existence of three broad line regions in the central part of the Akn 120. Long-term H? line shape variations in spectra of this galaxy are discussed.

Spatial structures in optical parametric amplification

We analyze the spatial aspects of the down-converted field emitted by a cavityless optical parametric amplifier, both from theoretical/numerical and experimental viewpoints. Our model neglects pump depletion and includes a classical description of the noise which initiates the process. The ringshaped angular distribution in the far field is determined basically by the phase-matching conditions. In the near field, the configuration arises from the superposition of contributions from a broad frequency band; it is shown that the finite duration of the pump pulse introduces a correlation among neighboring frequencies that allows for the appearance of a spotlike spatial modulation. When the spatial configuration of the pump field is changed from a plane wave to a narrow Gaussian, the near-field pattern assumes the form of a roll structure. The experimental observations obtained with a lithium triborate crystal agree qualitatively well with the theoretical picture.

Broadband X‐Ray Observations of the Narrow‐Line X‐Ray Galaxy NGC 5506

To address the nature of the Fe Kα line profile and the X-ray in the Seyfert 2 galaxy NGC 5506, we have performed a broadband X-ray analysis of data obtained with ASCA and ROSAT. Variations of up to 70% in the 2-10 keV band flux are detected during a 1 day ASCA observation performed in 1997 January, while no significant change in the 2-10 keV continuum shape is found. The ASCA spectrum consists of an absorbed power law, a soft excess below 2 keV, and an Fe Kα emission line at 6.4 keV. The soft excess can be well described either by thermal emission from very low-abundance material at a temperature kT0.8 keV or by scattered/leaking flux from the primary power law plus a small amount of thermal emission. The luminosity of the thermal emission in the former case is 1.2 × 1040 ergs s-1 over the 0.5-2 keV band, while the is ~1% of the intrinsic hard X-ray continuum in the latter case. Analysis of ROSAT HRI data confirms that the X-ray emission is extended on kpc scales in this object, and the extended component may account for most of the X-ray observed by the ASCA. The result suggests that in type 2 active galactic nuclei (AGNs), the soft excess comes at least partly from an extended region, causing a serious problem for the model in which the source is partially covered. We argue that the generally low abundances are a drawback for the single temperature thermal model and favor a scattering-dominated model. The scatterer is likely to be relatively cold (kT1 keV) in this object. The Fe Kα profile is complex and cannot be satisfactorily modeled by a single Gaussian. Models of either double Gaussians, or a narrow Gaussian plus a line from a relativistic accretion disk viewed at an inclination of about 40° ± 10° provide good fits to the data. However, the inclination of the disk can be substantially larger if there is a small amount of excessive Fe K edge absorption. The intermediate inclinations for narrow-line X-ray galaxies are consistent with a model in which the inner accretion disk is aligned with an outer obscuring torus.

Viscometric Functions for a Dilute Solution of Polymers in a Good Solvent

A dilute polymer solution is modeled as a suspension of non-interacting Hookean dumbbells and the effect of excluded volume is taken into account by incorporating a narrow Gaussian repulsive potential between the beads of each dumbbell. The narrow Gaussian potential is a means of regularising a delta-function potential---it tends to the delta-function potential in the limit of the width parameter going to zero. Exact predictions of viscometric functions in simple shear flow are obtained with the help of a retarded motion expansion and by Brownian dynamics simulations. It is shown that for relatively small non-zero values of the width parameter, the presence of excluded volume causes a swelling of the dumbbell at equilibrium, and shear thinning in simple shear flow. On the other hand, a delta function excluded volume potential does not lead to either swelling or to shear thinning. Approximate viscometric functions, obtained by assuming that the bead-connector vector is described by a Gaussian non-equilibrium distribution function, are found to be accurate above a threshold value of the width parameter, for a given value of the strength of excluded volume interaction. A first order perturbation expansion reveals that the Gaussian approximation is exact to first order in the strength of excluded volume interaction. The predictions of an alternative quadratic excluded volume potential suggested earlier by Fixman (J. Chem. Phys., 1966, 45, 785; 793) are also compared with those of the narrow Gaussian potential.

ASCA and ROSAT observations of the NLXG NGC 5506

Results of the analysis of the ASCA and ROSAT HRI data are presented. We find: (1) The flux in the 2–10 keV band varies by a factor of 70% during 1 day of ASCA observation. (2) The ASCA spectrum consists of a main power-law typical of Seyfert 1 galaxies absorbed by a column density ⋍ 3 × 10 22 cm −2 , a soft excess below 2 keV and an Fe Kα emission line. (3) The Fe Kα line profile is complicated and can be well fitted with a double gaussian or a narrow gaussian plus an emission line from a relativistic acrretion disk viewed at an inclination of ⋍ 40°. (4) The soft X-ray can be described by either thermal emission from very low abundant gas at temperature kT⋍ 0.8 keV or scattered/leaking flux from the primary power-law plus a small amount of thermal emission. (5) ROSAT HRI data reveal that the soft X-ray emission is extended on kpc scales, and the extent emission may account for the ASCA soft excess. These results are consistent with predictions from the unification model.

Diffraction by volume gratings with imaginary potentials

A medium described by an imaginary potential (or imaginary (refractive index) 2 ), that varies sinusoidally in one direction, acts as a volume grating for plane waves incident on it obliquely or normally. Two peculiar features are identified. First, if the potential is weak, so that there are only two significant diffracted beams near the Bragg angle, and three for normal incidence, diffraction is strongly affected by degeneracies of the non-Hermitian matrix generating the 'Bloch waves' in the grating; the effect of these degeneracies is very different from that of the Hermitian degeneracies for transparent gratings. Second, if the potential is strong and the grating thick, the asymptotic distribution of intensities among the diffracted beams (momentum distribution) is a rather narrow Gaussian, and dominated by a single set of complex rays; this is very different from the semiclassical limit for transparent gratings, where the rays form families of caustics proliferating with thickness, and with a wider momentum distribution.

Edge detection using local histogram analysis

A novel automatic edge extraction algorithm, based on investigation of local histograms of small non-overlapping blocks of the output of the first derivative of a narrow 2D Gaussian filter, is presented. It is shown that the proposed algorithm provides the best trade-off between noise suppression and correct edge localisation.

Surface charges and zeta potentials on polyethersulphone heteroporous membranes

Two microporous polyethersulphone filters are studied. The pore size distributions are obtained by an air-liquid displacement method. These distributions are narrow Gaussians with mean pore sizes over the nominal ones. The membranes are bathed by several diluted aqueous solutions of NaCl at 298 K. The equations of transport through the Gaussian distributed capillary pores of these membranes (Nernst-Planck, Navier-Stokes, Poisson, and charge and mass conservation laws) are numerically solved with the adequate limit conditions and used to obtain the electrokinetic coefficients for an assumed pore charge. The streaming potential is measured allowing to obtain the adsorbed surface charge density as a function of concentration (adsorption isotherm). The so obtained results are seen to deviate only slightly from those that should be obtained if all the pores were assumed equal to the most probable one (homoporous membrane). A Langmuir chloride adsorption mechanism fits well to the complete adsorption isotherm obtained; while a Freundlich or heterogeneous adsorption pattern could be assumed for low concentrations. Moreover, by an adequate correction of both the Langmuir and Freundlich equations to take into account the complex structure of the electrical double layer, the proper charges of the membranes are evaluated. These proper charges seem to be negligible in our case. Whereas, the average adsorption free energy and the maximum number of accessible sites are evaluated being relatively small, according to the hydrophillic character assumed for the membranes.

Iron Kα Evidence for Two X‐Ray Reprocessors in MCG −5‐23‐16

We report a remarkable Fe Kα fluorescence line profile in the Seyfert 1.9 galaxy MCG -5-23-16. The line is complex, consisting of a narrow core located at the galaxy's systemic velocity and wings to the red and blue sides of the core. This represents only the second detection with ASCA of an Fe Kα line profile with significant broadening blueward of 6.4 keV, consistent with Doppler boosting. The line core has an EW of ~60 eV and the wings have a combined EW of ~200 eV. The entire profile cannot be easily modeled with an emission line predicted from standard accretion disk theories. Instead, the line is marginally triple-peaked and is best described with three Gaussians having rest energies of 5.37+ 0.23−0.19 keV (FWHM = 30,200 km s-1), 6.37 ± 0.04 keV (FWHM < 6,600 km s-1), and 6.58+ 0.35−0.38 keV (FWHM = 75,300 km s-1). The line can also be modeled with a narrow Gaussian at ~6.4 keV and an emission line from an accretion disk viewed at an inclination angle of ~30° to 65°, depending on the ionization state of the gas. Within the context of the unified model, the most likely physical description of the complex profile is a superposition of an emission line from an accretion disk and a line that arises far from the disk in either the obscuring torus or the broad line region. This represents the first strong evidence for emission from two distinct X-ray reprocessors within a single Seyfert 1-type galaxy.

THE SUPERCRITICAL ACCRETION DISK OF SS 433

The structure of the SS 433 supercritical accretion disk derived from spectral and photometric data is described. In the disk plane, gas outflows at a velocity of about 100-150 km/s, while above the disk plane, the velocity increases sharply and reaches ≈ 1500 km/s at polar angle ≉ 60°. The outer parts of the accretion disk are involved in the precessional motion, which means that the slaved disk precession model is correct. There is complex periodic variability in the radial velocities of SS 433. Apart from the well-known precessional and orbital variability, the strongest cycle is 1/7 of the precession period, P7 = 23.228 ± 0.005 days. This is interpreted as evidence for a spiral shock in the accretion disk. The He II λ4686 line consists of two components: a stream-formed narrow Gaussian profile and a broad double-peaked one. The latter is completely eclipsed at phase 0.0. Its blue and red peaks are probably emitted in gaseous cocoons around the bases of the relativistic jets. A correct value of the mass function has been found, which shows that the optical star is massive. The relativistic star's mass is estimated to be Mx ≳ 6M⊙.

Spontaneous optical patterns in an atomic vapor: observation and simulation

Abstract Optical pattern formation in an experiment with single mirror feedback is described. The nonlinear medium is sodium vapor in a buffer gas atmosphere. A microscopic model is given and a stability analysis and numerical simulations are performed. Good agreement between the results of the experiment and the simulation is obtained. By numerical treatment of the model for the case of a plane incident wave (large aspect ratio), the results obtained with a narrow Gaussian beam (small aspect ratio) are traced back to the transition from hexagon to roll formation via ‘mixed’ states.

A neutralization-reionization mass spectrometric study of alkyl hydroperoxide cation radicals and four distinguishable [C,H 3,O 2] + isomers

The cation radicals of simple alkyl hydroperoxides ROOH + (R = CH 3, C 2H 5, iso-C 3H 7, tert-C 4H 9) have been studied by various mass spectrometric techniques, and neutralization-reionization (NR) methods in particular. Collisional activation (CA) of the beam of fast neutrals before reionization (NCR) and collision experiments with the mass-selected survivor ions (NR/CA) demonstrate that the peroxide OO bond remains intact in ionized methyl hydroperoxide. In the series of hydroperoxides, the abundances of the survivor ions decrease with α-substitution, which can be traced back to increasing contributions of [ R + OOH ] ion/dipole complexes to the parent ion beam. For the elucidation of ion structures, +NR − experiments are shown to be particularly helpful; in addition, they also provide insight into the bonding situations in hydroperoxides. Unimolecular loss of H' from metastable ions (MI) of CH 3OOH + leads to hydroperoxy methyl cations, CH 2OOH +, which are characterized by their MI/CA mass spectra. For comparison, four distinguishable [C,H 3,O 2] + isomers (CH 2OOH +, CH 3OO +, HC(OH) 2 , and H 3O +·CO) have been generated and examined by MI, CA, and NR experiments. With the exception of the proton-bound species H 3O +·CO, the corresponding neutral [C,H 3,O 2] . radicals exist as well and do not interconvert into each other. In addition, HOCH 2O . radicals can be probed by −NR + experiments with HOCH 2O − anions. Unimolecular and collision-induced decomposition of CH 2OOH + gives rise inter alia to a composite [C,H 2,O] + peak, which consists of a narrow gaussian and a broad, dish-topped component. The narrow component vanishes in the +NR + experiment.

New description of charged particle propagation in random magnetic fields

When charged particles spiral along a large constant magnetic field, their trajectories are scattered by random components that are superposed on the guiding field. In the simplest analysis of this situation, scattering causes the particles to diffuse parallel to the guiding field. At the next level of approximation, moving pulses that correspond to a coherent mode of propagation are present, but they are represented by delta-functions whose infinitely narrow width makes no sense physically and is inconsistent with the finite duration of coherent pulses observed in solar energetic particle events. To derive a more realistic description, the transport problem is formulated in terms of 4 x 4 matrices, which derive from a representation of the particle distribution function in terms of eigenfunctions of the scattering operator, and which lead to useful approximations that give explicit predictions of the detailed evolution not only of the coherent pulses, but also of the diffusive wake. More specifically, the new description embodies a simple convolution of a narrow Gaussian with the solutions above that involve delta-functions, but with a slightly reduced coherent velocity. The validity of these approximations, which can easily be calculated on a desktop computer, has been exhaustively confirmed by comparison with results of Monte Carlo simulations which kept track of 50 million particles and which were carried out on the Maspar computer at Goddard Space Flight Center.

Optically detected magnetic resonance (ODMR) study of poly(3-hexylthiophenacetylene (P3HTA) films

The photoluminescence (PL) and X-band ODMR of poly(3-hexylthiopheneacetylene) (P3HTA) films is descried and discussed. As in poly(3-alkylthiophenes) (P3ATs), poly(p-phenylenevinylenes) (PPVs), poly( p-phenyleneacetylenes) (PPAs), and their derivatives, three PL-enhancing ODMR features are observed. The strongest is a narrow assymetric ( Δ H 1 2 t 14 G ) line which is the sum of a broad Gaussian at g ≈ 2.0032 ± 0.0007 and a narrow Gaussian at g ≈ 2.0022 ± 0.0007. This asymmetry is slightly weaker than that found in P3ATs, but much stronger than in PPVs and PPAs. Since the resonance is attributed to polaron-polaron fusion into nongeminate singlet excitons, the lineshape thus indicates that P3HTA is more charge conjugation symmetric than P3ATs but less than PPVs and PPAs. The other two features are a broad full-field and a narrower half-field triplet powder pattern, attributed singlet exciton generation via triplet-triplet exciton fusion. However, while the half-field resonance of P3ATs, PPVs, and PPAs displays a single line, that of P3HTA is clearly resolved into two peaks. The nature of these observations is discussed in relation to disorder effects.

Doppler ultrasound spectral shape in the poststenotic velocity field

The shape of averaged and smoothed pulsed Doppler spectra from the shear layer between jet and recirculation zones, one diameter downstream of three acrylic stenosis (27, 47 and 65% diameter reduction) in a steady flow dialysis tubing model, were found to be complex. Their shape contrasted with the shape of spectra from regions of jet breakup. The latter had a shape suggesting a Gaussian distribution of apparent velocities consistent with varying magnitude and direction in turbulent flow. In contrast, the least complex spectra from the shear layer had a double-peaked shape suggestive of two distinct major velocity components or streamline groups. A subtraction method was used to resolve the least complex spectra into two relatively narrow Gaussian components. More complex spectra could be resolved into multiple components by serially subtracting individual Gaussian components. Comparison with the pattern of particles revealed by flow visualization studies suggests that most of the components are due to axially directed streamline groups of different velocities but that some may be due to radially directed streamline groups. Broadened spectral components, which are apparent at higher flow rates, are consistent with development of vortices in the shear layer.

Optically detected magnetic resonance (ODMR) of polarons and charge-conjugation symmetry in conducting polymers

The main narrow photoluminescence(PL)-enhancing g = 2.0025 ± 0.0010 X-band ODMR of poly(3-alkylthiophene) (P3AT) and poly(2,5-dialkoxy paraphenylenevinylene) (PDOPV) films, solutions, and blends is described and discussed. The resonances all closely match a sum of narrow and broad Gaussians. In P3AT the narrow Gaussian saturates at a lower power than the broad Gaussian. While this ODMR is believed to result from intrachain ‘distant pair’ polaron recombination, the assignment of each Gaussian to the proper polaron is undecided. The g-values of the two Gaussians are nearly identical in PDOPV, apparently reflecting a very high degree of charge-conjugation symmetry (CCS). They are, however, quite distinct ( g = 2.0032, 2.0019, respectively) in P3AT, possibly due to the sulphur heteroatom on the thiophene rings. The ramifications of this CCS violation for the PL quantum yield are discussed. In all cases, the spectral dependence of the narrow resonance is similar to the PL spectrum, indicating that the polaron levels are close to the band edges and to the levels of the (presumably) short-lived geminate singlet excitons. The sensitivity of the ODMR intensity to sample processing suggests that it may possibly be affected by an unidentified native, possibly conformational, defect. The decay modes competing with polaron recombination are also discussed.

Effect of Small Stress Ranges on Fatigue Crack Propagation under Random Loading

This is a part of the serial studies on the experimental method to infer fatigue life of a structural member under service loadings. When a load profile can be approximated by a narrow band stationary Gaussian random process, it has been pointed out that random fatigue tests are easily done with a personal computer by simulating the envelope of the process by FFT. However, it may not be realistic to repeat a time and cost consuming test to get the probability distribution function of fatigue life. In this study a method is proposed to make the total experimental hours as short as possible by eliminating small amplitude cycles, that is, an experimental procedure is established to see the effect of the elimination and determine the cut-off-level beforehand.

Tangential breast irradiation: influence of technique of set-up on transfer errors and reproducibility

Using conventional portal films, the influence of the technique of set-up on the transfer error from simulator to treatment couch and on the subsequent reproducibility was made for the irradiated volume in the treatment of breast cancer. A total number of 376 portal films have been performed on 14 patients. All the patients were treated on a 6 MV Linac supplied with an automatic verification system excluding, however, the couch parameters. The overall precision of the treatment delivery is evaluated by the global analysis of the discrepancies between the simulator films and the different portal films. For the patient group lying on a inclined plane with (group 2) or without (group 1) fixed arm support, a narrow gaussian distribution is obtained in the anteroposterior (AP) direction with a SD of 4 mm. In the craniocaudal (CC) direction, the frequency of distribution of the patients treated without fixed arm support is much larger than in the other group: the SD is respectively 15.5 mm for the first and 5.5 mm for the second one. The reproducibility of the series of set-ups of the two groups estimated by reference to the mean value are similar in the AP direction. The SD within the series of portal films in the CC direction is 5.8 mm for the first group and 3.7 mm for the second group. Their comparison with the discrepancies of 15.5 mm and 5.5 mm when assessing the deviation between the simulated and portal films shows the importance of systematic errors. The localisation of the irradiation port can be improved by using support systems with fixed arm indicators.

Vernier acuity: Effects of chromatic content, blur and contrast

Offset thresholds were measured for targets whose horizontal profiles were either Gaussian or odd-symmetric Gabor functions. The targets were defined either by variation along the constant B or the constant R & G axes of color space or by luminance variation. Blur was varied in the case of the Gaussian targets by varying the standard deviation of the distribution and in the case of the Gabor functions by varying the spatial frequency of the sinusoidal component. Detection thresholds for all the stimuli were measured. The contrast of the targets used in the measurement of offset thresholds was varied from just above detection threshold to the maximum that could be produced. The offset thresholds obtained with targets of different chromatic composition are nearly identical when blur and contrast relative to detection threshold are held constant. We attribute the slight advantage held by luminance targets over chromatic targets for narrow Gaussians to the detectability of low frequency components of the chromatic targets which are of little use in the assessment of offsets. This conjecture is supported by the complete absence of such an advantage in the case of Gabor targets.

A signature of the intermittency of interstellar turbulence - The wings of molecular line profiles

Ensembles of line profiles of molecular clouds are presented, and it is shown that most of the profiles can be fitted by a strong and narrow Gaussian plus a weak and broad Gaussian. The remarkably self-similar scaling of the wing widths to that of the cores is shown and the available information on the density and velocity structure of the fast gas is discussed. It is shown that the line wings can be used as tracers of the probability distribution of the projected velocity field within the cloud volume sampled by the profile. The statistical properties of this distribution are compared with that of the velocity in atmospheric turbulence and recent duct flow measurements. 62 refs.