Apparent Wavelength Research Articles

Purkinje-muscle reentry as a mechanism of polymorphic ventricular arrhythmias in a 3-dimensional model of the ventricles.

Multiple electrode mapping of the ventricles during complex tachyarrhythmias has revealed focal subendocardial activation whose mechanism remains unexplained. We hypothesized that reentry involving the Purkinje-muscle junctions (PMJs) may be a mechanism for such focal excitations. We have constructed an anatomically appropriate computerized 3-dimensional model of the mammalian ventricles that includes the Purkinje conduction system and 214 PMJs distributed throughout the endocardium. Isochronal maps during normal excitation, as well as during right or left bundle branch block, resembled experimental measurements and compared well with isochronal maps of propagation in the human heart. Activity observed at both sides of a PMJ in the model showed that propagation from Purkinje fibers to muscle was slower than in the opposite direction. Under these realistic and normal conditions, the evolution of reentrant activity involving muscle and the Purkinje network was simulated. The reentry pattern was independent of the initiation site. It evolved with drifting epicardial breakthroughs and transformed on the endocardium from focal activity to figure-of-8 reentry. In addition, the ECG amplitude undulated during the evolution, and decrease in the cycle period, apparent wavelength, and propagation velocity were observed. Finally, the reentry was terminated if the Purkinje system was disconnected from the muscle before it reached a relative steady state. The simulation results suggest the following: (1) Epicardial breakthroughs and endocardial focal activity may originate at the PMJs. (2) The ECG amplitude may decrease as the reentry stabilizes and the excitation wavelength decreases. (3) The Purkinje system may have a double role in the evolution of reentry: first, it is essential to the reentry at the initial stage; second, it may lead to the establishment of intramyocardial reentry, at which time the Purkinje system becomes irrelevant.

Multiphoton excitation of the DNA stains DAPI and Hoechst

,6-diamidino-2-phenylindole hydrochloride (DAPI) andHoechst 33342 were found to display two- or three-photon excitation from 810 to 910nm. We examined the effect of excitation wavelength on the mode of excitation forDAPI and Hoechst 33342 in the solvent isobutanol and when bound to double helicalDNA. For DAPI and Hoechst 33342 in isobutanol the mode of excitation changed fromtwo- to three-photon excitation over this wavelength range, with apparent transitionwavelengths of 855 and 880 nm, respectively. However, when bound to DNA, thetransition wavelength from two- to three-photon excitation increased for both probes.In the case of DAPI–DNA, the apparent transition wavelength increased to 868 nm,and three-photon excitation occurred above 900 nm. For Hoechst 33342–DNA themode of excitation was a mixture of two- and three-photon excitation to the longestexcitation wavelength of 910 nm, and we were unable to observe pure three-photonexcitation for Hoechst 33342–DNA. In the transition region the anisotropy of DAPIwas dependent on laser power, illustrating that the mode of excitation and transitionwavelengths will depend on the precise experimental conditions. Higher spatialresolution was observed for three-photon excitation of DAPI than for two-photonexcitation of Hoechst 33342. These results suggest that these probes can be used foreither two- or three-photon imaging of DNA or chromosomes.Keywords: fluorescence, spectroscopy, imaging, time-resolved fluorescence,two-photon excitation, three-photon excitation, DAPI, Hoechst 33342, two-photonmicroscopy

Spectrofluorometric trace determination of cerium(III) in sodium hexametaphosphate solutions.

The use of sodium hexametaphosphate in the spectrofluorometric determination of trace amounts of cerium(III) ions is described. Sodium hexametaphosphate acts as a specific reagent for enhancing the fluorescence intensity of cerium(III) in aqueous solutions. The apparent excitation and fluorescence wavelength used are 304 and 344 nm, respectively. Maximum fluorescence intensity is obtained by irradiating Ce(III) dissolved in 5.346 g/l sodium hexametaphosphate solution at room temperature. The fluorescence varies linearly with the concentration of cerium(III) in the range of 0.001-60 microg/ml. The coefficient of variation for 45 microg/ml Ce(III) in 5.346 g/l sodium hexametaphosphate solution is 1. The quenching effects of other lanthanides and some inorganic anions are given. This technique permits a direct and rapid determination of cerium(III) in rare earth mixtures and cerium concentrates.

Experimental demonstration of the "apparent wavelength"

In this paper, an experimental demonstration of the apparent using microwaves incident on a plane conductive surface obliquely, with the electric field polarization parallel to a reflecting plane, is presented. Standing wave measurements were obtained by utilizing the interaction between the transmitting and the receiving rectangular horn antennas using the receiving horn antenna as a probe. This technique demonstrates to the students that the wavelength along the normal, the apparent is longer than the wavelength of the free-space incident or reflected waves and is in agreement with the theory. Finally, the proposed technique demonstrates high sensitivity and accuracy for tutorial demonstrations of standing wave pattern measurements despite the large cross-section of the receiving antenna. >

The Choice of a Vertical Grid for a 2.5D Numerical Model of the Middle Atmosphere

Abstract The consequences of choosing an unstaggered grid (UG), Charney-Phillips-type grid (CPG), or Lorenz-type grid (LG) in the vertical for a 2.5D model are examined. Analytical solutions for the linearized and scaled eddy equations in spherical coordinates are compared to solutions obtained by finite-difference methods. Waves with vertical structure greater than six gridpoint intervals are reliably reproduced by the model using any of these three grids. Waves with vertical structure between four and six gridpoint intervals appear in the model with shorter vertical wavelengths using the UG and CPG, and with longer vertical wavelengths using the LG. Waves with vertical structure less than four gridpoint intervals will be evanescent using the UG and CPG. Waves with vertical structure less than four gridpoint intervals will be propagated vertically using the LG; however, waves unresolved by the LG will spuriously appear and will be vertically propagated with an apparent vertical wavelength of three gridpo...

Development of a Supermirror Neutron Guide Tube.

A supermirror neutron guide tube with a characteristic wavelength of 1.2 A was developed and installed at the Kyoto University Reactor (KUR). The apparent critical wavelength of the present supermirrors is about 250 A. The geometrical parameters of the guide tube are: 11.7 m total length, and 10 mm wide X74 mm high beam cross section. The supermirror neutron guide tube presents decisive advantages over the conventional nickel mirror guide tube higher transmission of neutrons, brought about through the contribution of neutrons of shorter wavelengths and of those presenting large divergent angles. The total neutron flux obtained from the KUR supermirror guide tube is about 5x107n/cm2·s, which is about 25 times what is obtainable with the conventional KUR nickel mirror neutron guide tube of the same geometrical parameters.

Fluctuation in structure of inclusion complexes of cyclodextrins with fluorescent probes

The lifetime distribution of the fluorescence from inclusion complexes of cyclodextrins with anilinonaphthalenesulfonates (ANSs) was analyzed by time-correlated single-photon counting measurements. The very large width of the lifetime distribution as well as the dependence of the apparent maximum wavelength of the fluorescence on the excitation wavelength indicates that the conformation of the excited TNS molecules in cyclodextrin cavities is distributed within a wide range. These observations indicate a striking similarity between the fluorescence of fluorophores in proteins and that in the inclusion complexes.

On the directional sensitivity of motion detectors

The output of a motion detector depends on the direction of pattern motion, relative to the axis defined by its two input elements. Usually a cosine shaped directional sensitivity characteristics is assumed: The response is strongest for pattern motion along the detector axis, reversing its sign for motion in opposite direction; for motion perpendicular to the detector axis it is expected to be zero, with intermediate values for oblique motion directions. However, geometric considerations show that this expectation is by no means trivial. When a periodic pattern moves along a direction a relative to the detector axis, the spatiotemporal intensity distribution along the detector axis can be described by its apparent spatial wavelength and its apparent velocity, which both vary with 1/cos?. In consequence, a motion detector depending exclusively on the apparent velocity of the stimulus would respond strongest to gratings moving perpendicular to the detector axis, whereas motion along the detector axis would yield the smallest response in such a detector. The response of a motion detector of the correlation type, on the other hand, is determined by the ratio between velocity and wavelength, the temporal frequency, which is not influenced by the direction of pattern motion, and by the ratio between sampling base and the wavelength. The latter feature leads to a cosine-shaped directional characteristics for large pattern wavelengths. However, for smaller wavelengths specific deviations from a simple harmonic are expected. These expectations were confirmed by the simulation of an elementary motion detector model and extended for a slightly more elaborated model. Representing a biological motion detecting unit of the correlation type, the directional characteristics of the H1 interneuron in the fly's brain was investigated electrophysiologically, and compared to the simulations.

Relation of the spectroscopic reflectance of olivine to mineral chemistry and some remote sensing implications

Using high‐resolution visible and near‐infrared diffuse spectral reflectance, we have systematically investigated apparent wavelength shifts as a function of mineral chemistry in the Fe/Mg olivine series from Fo11 to Fo91. The study also shows that trace amounts of nickel can be spectrally detected in the olivine structure. We show that significant compositional information can only be extracted at relatively high resolution, because the overall spectral characteristics of the olivines change only subtly as a function of the Fe/Mg ratio. Significant spectral variation as a function of grain size is also demonstrated, adding a further complication to the interpretation of remotely sensed data from olivine‐rich surfaces. This laboratory study is expected to aid in the interpretation of remotely sensed data from both terrestrial and extraterrestrial bodies. Terrestrial applications may include the recognition of ultramafic, ultrabasic, and basaltic terrains which in themselves may have mineral potential. Among extraterrestrial applications, the asteroids are obvious candidates for further examination if instrumentation can provide the necessary wavelength coverage, resolution, and signal‐to‐noise ratio so that spectra can be compared to those laboratory data discussed here. Some permutations of Fe‐Mg‐Ni relations in olivines are discussed as they apply to the interpretation of asteroid surfaces and other extraterrestrial bodies.

Plasma wave wigglers for free-electron lasers

We explore the possibility of using a relativistic plasma density wave as a wiggler for producing free-electron laser radiation. Such a wiggler is a purely electric wiggler with frequency ω <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</inf> (plasma frequency) and wavenumber k <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</inf> . If an electron beam is injected parallel to the plasma wave wavefront, it is wiggled transversely with an apparent wiggler wavelength <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\lambda_{w} = 2\pi c/\omega_{p}</tex> . Using plasma densities in the 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sup> (cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> ) range, λ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">w</inf> of order 100 μm may be obtained, thereby permitting generation of short wavelength radiation with modest energy beams. The effective wiggler strength <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a_{w} = eA/mc^{2} \sim 0.5</tex> can be extremely large. We discuss the excitation methods for such wigglers and examine the constraints imposed by the plasma medium on FEL gain in this scheme.

To: “High‐resolution common‐depth‐point reflection profiling: Field acquisition parameter design,” by R. W. Knapp and D. W. Steeples, which appeared in February 1986, GEOPHYSICS, p. 283–294

The following errors have been detected. p. 288, left column, 3rd paragraph: Change (Figure 4, Knapp and Steeples, 1986, this issue) to (Figure 3, Knapp and Steeples, 1986, this issue). p. 288, right column, 3rd complete paragraph, 3rd sentence: Change “…when the length of the array is equal to about one‐fourth the apparent surface wavelength…” to “…when the length of the array is equal to about one‐half the apparent surface wavelength…”. Next line, change “ [Formula: see text]” to “[Formula: see text]”. Next line, change “[Formula: see text].” to “[Formula: see text]”. Next line, change “one‐fourth” to “one‐half”. Next 2 equations, change “L ⩽ .25…” to “L ⩽ .5…” and [Formula: see text]…” to “[Formula: see text]…”. p. 289, left column: Change [Formula: see text] to [Formula: see text] Following paragraph, 4th line: Change “.75 m.” to “1.4 m.”; and change “When the maximum frequency value approaches and exceeds 100 Hz (apparent frequency equal to about 70 Hz),…” to “When the maximum frequency value approaches and exceeds 200 Hz (apparent frequency equal to about 140 Hz),…”.

High-resolution photography of the solar chromosphere. XXI Determination of the physical conditions in an H-alpha active-region loop

Values of the electron temperature, electron density, gas density, gas pressure, degree of hydrogen ionization, and other physical conditions are determined at seven locations along the axis of an H..cap alpha.. active-region loop observed on the solar disk. Combining these data with earlier results we present for the first time a fairly complete description of the true geometry, flow velocities, and thermodynamic conditions in such a loop at one moment of time. The physical conditions show a marked variation along the loop. The variations in density and pressure exhibit a wavelike nature, with an apparent wavelength of some 50,000--60,000 km. The results offer the prospect of putting observational constraints on theoretical models of coronal loops and of identifying the types of flows and waves present.

Global large scale structures in the F region

Measurements of neutral densities, neutral temperature, ion density and ion temperature by the Atmosphere Explorer C and E satellites exhibit fluctuations made up of coherent waves of scale sizes from hundreds to thousands of kilometers. The fluctuations in the AE‐C data are found at times of low magnetic activity to extend from the auroral region in one hemisphere across the equator to the corresponding region in the other hemisphere with little change in apparent wavelength. The fluctuations in the AE‐E data similarly exhibit at times of low magnetic activity nearly uniform wave structure encircling the equatorial belt. Typical examples of 2000 km waves in the AE‐C data and 1500 km waves in the AE‐E data are discussed. To explain these observations, it is suggested that during quiet periods the auroral belts excite quasi‐stationary waves distributed about the earth with coherent periods, possibly tidal, and scale lengths determined by the structure of the belts. According to this interpretation, TID's are manifestations of the transient waves that result from changes in magnetic activity with periods and scale sizes associated with the auroral excitation.

Optical Doppler imaging of the Aurora Borealis

The Fabry‐Perot spectrometer method of measuring upper atmospheric winds and temperatures has now been firmly established. The Michelson interferometer offers an alternative approach that has so far received little attention. A brief description is given of a stable achromatic field‐widened Michelson interferometer, that uses a CCD detector. Four phase‐stepped images are reduced to images of phase (leading to velocity), of fringe visibility (leading to temperature), and intensity. Preliminary results on the 557.7 nm emission in aurora, made during field trials in February, 1984 are presented. During an auroral brightening three scale sizes of event were observed in the velocity images: a "pulsation" filling the whole field of view and having a period of 200 s, a linear structure with an apparent wavelength of about 50 km, and a linear wavelike structure with an apparent wavelength of 10 km.

Noise attenuation by Vibroseis whitening (VSW) processing

Reflection seismic data recorded on the Atlantic Coastal Plain to examine suspected faulting of the shallow (200 m) basement were contaminated by severe ground roll noise with an apparent velocity of 587 m/sec, 25 Hz dominant frequency, and 23 m apparent wavelength. A receiver interval of 5 m and a total spread length of 285 m were used to obtain 24‐fold coverage. Although the noise problem was severe, overlapping source and/or receiver arrays on the surface were not used for the recording geometry in order to avoid a decrease in resolution caused by the smoothing effect of overlapping subsurface coverage. Instead, the large‐amplitude surface waves were attenuated by a process called Vibroseis® whitening (VSW). VSW is based on the application of time‐varying amplitude scaling before Vibroseis crosscorrelation. A conventional method of automatic digital gain control was found to be effective for this purpose. This scaling results in a signal‐to‐noise ratio improvement equal to the gain expected from crosscorrelation. The scaling window length and the length of sweep are the only parameters required to define the signal‐to‐noise improvement for a given swept‐frequency band. A shorter scaling window and longer sweep length give better results because of the higher gain obtained by crosscorrelation. An increase in the quality of Atlantic Coastal Plain data clearly showed that VSW processing resulted in high resolution on stacked sections and made it possible to map shallow basement reflections at 0.2 sec, revealing faults with up to 10 m offset. Reflections from the sedimentary section above basement also became distinct.

Attempt to determine some properties of the semidiurnal internal tide on the continental slope, Great Barrier Reef

An experiment designed to determine wave parameters of the internal semidiurnal tide near 18�S. off the Great Barrier Reef is described. It suffered from inaccuracy in position fixing, so no information on the vertical component of the phase speed was gained. Results for the horizontal component show an internal tide of wavelength 15 nautical miles and phase speed 60 cm s-1 propagating east to south-east, at a small angle to the isobaths. A mean current of 50 cm s-1 flowing towards the south-east along the isobaths deflects the outgoing wave; the apparent (observed) direction of propagation is eastward, the apparent phase speed is increased to 80 cm s-1 and the apparent wavelength to 20 nautical miles.

Ultraviolet continuum absorption /less than about 1000 A/ above the quiet sun transition region

view Abstract Citations (20) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Ultraviolet continuum absorption /less than about 1000 A/ above the quiet sun transition region Doschek, G. A. ; Feldman, U. Abstract Lyman continuum absorption shortward of 912 A in the quiet sun solar transition region is investigated by combining spectra obtained from the Apollo Telescope Mount experiments on Skylab. The most recent atomic data are used to compute line intensities for lines that fall on both sides of the Lyman limit. Lines of O III, O IV, O V, and S IV are considered. The computed intensity ratios of most lines from O IV, O V, and S IV agree with the experimental ratios to within a factor of 2. However, the discrepancies show no apparent wavelength dependence. From this fact, it is concluded that at least part of the discrepancy between theory and observation for lines of these ions can be accounted for by uncertainties in instrumental calibration and atomic data. However, difficulties remain in reconciling observation and theory, particularly for lines of O III, and one line of S IV. The other recent results of Schmahl and Orrall (1979) are also discussed in terms of newer atomic data. Publication: The Astrophysical Journal Pub Date: March 1982 DOI: 10.1086/159741 Bibcode: 1982ApJ...254..371D Keywords: Emission Spectra; Lyman Spectra; Oxygen Spectra; Solar Atmosphere; Solar Spectra; Ultraviolet Absorption; Calibrating; Opacity; Resonance Lines; Solar Physics full text sources ADS |

Effects of approximations in processing light scattering from rough surfaces by the stationary phase method

Electromagnetic field disturbance in the vicinity of a very rough interface is approached from two different points of view; first, by assuming that a large height roughness interface can be treated starting from a small height roughness model and second by gradually increasing from zero the difference in refractive index of both media separating a rough interface. Far-field diffraction from a ridge is also discussed when the incident field is not significantly disturbed as in the case of an immersion. Results derived from the stationary phase method are shown to be valid for various surface shapes of models, as long as the roughness height is larger than the apparent wavelength of the radiation (wavelength measured along the normal to the mean surface).

Apparent wavelength of a source to a moving observer

Apparent wavelength of a source to a moving observer

Bed Forms on West Florida Shelf as Detected with Side-Scan Sonar: ABSTRACT

A Side-Scan Sonar investigation on the west Florida shelf reveals a multitude of bed-form types. A nongenetic classification was devised based on apparent wavelength and ripple index (R.I. = Wavelength/wave height). This system divides the observed features into four groups: Giant--wavelength greater than 30 m, R.I. 30 to 100; Large--wavelength less than 30 m but greater than 1 m, R.I. 15 to 30; Small--wavelength less than 1 m, R.I. 5 to 15; and low-relief swells--wavelength greater than 300 m and relief only a few meters. Five major zones roughly parallel to the coast are delineated according to the distribution of bed-form types. Zone A, parallels the coastline out to approximately 20 m depth and is characterized by giant to large-scale bed forms. These features are observed on the sonographs as long, sinuous, and sometimes bifurcating, troughs of high reflectivity (coarse-grained?) sediment, interspaced with mounds of presumably finer grained material. Similar bed forms described in the literature have been labeled lineations. Zone B extends out to mid-shelf depth (40 to 100 m) and is characterized by low-relief swells and a few patches of giant to large-scale features. The low-relief swells at times correlate with large elliptical patches of apparently fine sand on a relatively coarser grained, flat, sea floor. Zone C is centered around the Florida Middle Grounds region and is characterized by small-scale bed forms and low-relief swells. These small-scale bed forms observed on the sonographs resemble current ripples. The orientation of these ripples varies from predominantly north-south across the Florida Middle Grounds to an east-west orientation in areas farther south. Zone D is situated offshore Cape San Blas along the Florida panhandle. The bed forms in this zone are characterized by high relief (2.0 to 8.0 m) giant-scale features. Superimposed on the giant-scale bed forms and on the sea floor fringing this zone are small-scale bed forms resembling current ripples. Zone E encompasses the outer shelf and is generally void of bed forms. However, a few unusual giant to large-scale features are observed. Most of the giant, giant to large, and large-scale bed forms on the west Florida shelf are considered to be storm-related features. Some giant-scale features and the low-relief swells may be relict structures left over from times of lowered sea level. The small-scale bed forms within Zone C are possibly the results of either internal waves or tides set up on the summer thermocline and/or currents created by Loop Current intrusion on the shelf. The latter event may also generate strong shelf-edge currents creating the bed forms in Zone E. End_of_Article - Last_Page 1687------------