Oblique Cone Research Articles

A novel filter with low angle effect

The filters with low angle effect are composed of high index dielectric layers and metallic layers laid alternately. When used in the case of oblique incidence or large cone angle incidence, this filter reduces shift of central wavelength significantly while still maintaining its filter characteristics. Theoretical and experimental studies show that such a novel filter can be used in the situation of both large incident angle and cone angle.This effect is due to the usage of high index material and its induced transmittance.

Oblique View Cone Beam Tomography for Inspection of Flat-Shape Objects

Oblique View Cone Beam Tomography for Inspection of Flat-Shape Objects

<i>Ankumia</i> van Veen, 1932 <i>(nomen dubium):</i> pathological moult retention in the Cytherellidae (Platycopida: Ostracoda)

Abstract. The monotypic genus Ankumia is associated with the rich cytherellid fauna described by van Veen (1932) from the Upper Cretaceous (late Maastrichtian) rocks of South Limburg, The Netherlands. The type species (A. bosqueti van Veen, 1932) is redescribed because the genus possesses the enigmatic combination of cytherellid (posterior sex-dimorphism and R/L overlap) and eridostracan (several concentric bands) characters. As no holotype was designated, the redescription is based on a detailed SEM examination of the syntypes in the Bonnema/van Veen composite collection. Most syntypes show that the outer layer of coarse, concentric, rings, which form an oblique cone, are retained moults of a species of cytherellid. The point of retention in the early instars is along the posteroventral margin, contrary to the dorsal position of successive lamellae in eridostracan Cryptophyllus. Other syntypes possess the typical lateral outline of adult species of Cytherellidae. The ontogeny of each individual of retained moults (‘Ankumia’) has a nine-instar pattern, with a growth increment between successive moults about 1.15, slightly less than that (about 1.20) observed by Shaver (1953) for Cytherella bullata. The name Ankumia is abandonned, and a new combination proposed for the previous type species, Platella bosqueti (van Veen, 1932).

Transmission of waves near the lower oblique resonance using dipoles in the ionosphere

The observations in the OEDIPUS‐C experiment of bistatic propagation along the lower oblique resonance cone between a separated transmitter and receiver in the ionosphere are explained through detailed calculations of the radiated field of the V‐dipole antenna used in the experiment and by a novel theory of the receiving antenna under resonance conditions. Unexpectedly high values of 25 kHz signal observed at the resonance and its structure agree well with calculations of the transmission between the exciter and receiver, when antenna layout and dispersive properties of the plasma at resonance are taken into account.

Electromagnetic whistler‐mode radiation from a dipole in the ionosphere

Dipole‐antenna radiation theory has been tested for electromagnetic whistler‐mode waves in the frequency range 0.1–1.3 MHz using data from the two‐point rocket experiment Observations of Electric‐field Distributions in the Ionospheric Plasma; a Unique Strategy (OEDIPUS) C. Waves were emitted from a double‐V dipole on a transmitting subpayload and received at a distance of about 1200 m on a similar dipole connected to a synchronized receiver. The magnitudes of transmitted signals predicted by a theory for short dipoles have been found to be in good agreement with observations. The agreement is very good in the top two thirds of the frequency range where the dispersion relation and the geometry provide only one saddle‐point solution with the required group direction. In this part of the parameter space studied, the transmitter‐receiver separation is at least 10 wavelengths. This is not always true at the lowest frequencies, where the expected effects of interference of multiple saddle‐point rays and of the oblique resonance cone are observed.

Potential structure near a probe in a flowing magnetoplasma and current collection

The distributions of plasma and potential near an electric probe in a relative motion with respect to a magnetized plasma are studied by means of three‐dimensional (3‐D) numerical simulations. The relative motion is simulated by a plasma flowing past the probe across the ambient magnetic field. The plasma flow is imposed by a convection electric field . A probe with a positive potential bias is considered. The prominent features of the potential distribution include (1) wings of positive potential perturbations extending along the magnetic field and swept forward in the direction of the plasma flow and (2) a “fan” shaped structure in planes transverse to the magnetic field in the region where the convection electric field is opposed by space charge electric fields. The wing‐like structure can be interpreted in terms of electrostatic plasma waves belonging to the oblique resonance cone in a magnetized plasma. The relative flow causes the formation of a “bow shock” in front of the probe, where plasma density is enhanced due to the combined effect of the retardation of the flowing ions and the modification in the drift of the electrons in the sheath of a positive probe. The electron collection by the probe is significantly enhanced above the theoretical upper bound current obtained from the conservation of energy and the canonical angular momentum for the case without the relative motion. The current in the plasma, contributing to the collection of electrons by the probe, flows in a magnetic field‐aligned channel in the vicinity of the probe where electric fields parallel to the magneitc field are relativley strong. Electron flux is fed into the channel all along its length by the drift in the self‐consistent electric field, considerably enhancing the current collected by the probe. The field‐aligned current channel is localized near the probe where parallel electric fields dominate; it does not extend to infinity along the probe's magnetic shadow, unlike that for the case of a nonflowing plasma.

A three-dimensional morphometrical study of the distal human femur.

The objective of this paper is to present a method to describe the three-dimensional variations of the geometry of the three portions forming the distal part of the human femur: the medial and lateral femoral condyles and the intercondylar fossa. The contours of equally spaced sagittal slices were digitized on the distal femur to determine its surface topography. Data collection was performed using a digitizer system which utilizes low-frequency, magnetic field technology to determine the position and orientation of a magnetic field sensor in relation to a specified reference frame. The generalized reduced gradient optimization method was used to reconstruct the profile of each slice utilizing two primitives: straight-line segments and circular arcs. The profile of each slice within the medial femoral condyle was reconstructed using two circular arcs: posterior and distal. The profile of each slice within the lateral femoral condyle was reconstructed using three circular arcs: posterior, distal and anterior. Finally, the profile of each slice within the intercondylar fossa was reconstructed using two circular arcs: proximal-posterior and anterior, and a distal-posterior straight-line segment tangent to the proximal-posterior circular arc. Combining the data describing the profiles of the different slices forming the distal femur, the posterior portions of each of the medial and lateral femoral condyles were modelled using parts of spheres having an average radius of 20 mm. The anterior portion of the lateral condyle was approximated to a right cylinder having its circular base parallel to the sagittal plane with an average radius of 26 mm. The anterior portion of the intercondylar fossa was modelled using an oblique cylinder having its circular base parallel to the sagittal plane with an average radius of 22 mm. Furthermore, it is suggested that the distal portion of the lateral femoral condyle could be modelled using parts of two oblique cones while the distal portion of the medial femoral condyle could be modelled using a part of a single oblique cone, all cones having their circular bases parallel to the sagittal plane. It is also suggested that the posterior portion of the intercondylar fossa could be modelled using two oblique cones: a proximal cone having its base parallel to the sagittal plane and a distal cone having its base parallel to the frontal plane.

Oblique cone formation in Ge by Ar + sputtering

Sharp oblique cones are only formed on polished germanium surfaces by 30 keV Ar + bombardment, in the presence of tungsten seed atoms; substantiating Wehner's hypothesis that higher melting point seed material is the crucial factor for come formation. The morphology of the cone is characterized by the formation of a sloped ridge, consistent with the observations of earlier workers. Moreover, some strange wing-like structures are associated with these cones.

Redeposition behavior of seeds in oblique cone evolution

Cones developed on Cu surfaces bombarded with an obliquely incident Ar+ –ion beam, while simultaneously supplying Mo ‘‘seeds’’ by sputtering, were observed by scanning and transmission electron microscopy. Seed atoms were found to preferentially deposit on the cone slopes which received high fluxes of these species, forming crystalline thin layers there. The seed overlayers thus grown were ribbon-like in configuration and composed of Mo crystallites arranged in a preferred orientation. An explicit relationship was found between the crystallographic orientations of overlayer and substrate, but it was inconsistent with the existing model of epitaxy. Also, the cone population decreased with decreasing local seed flux and vice versa for the average cone dimension. This may indicate that the key role of seeds is to promote the nucleation of cones, not to enhance the development of nucleated cones.

Ray-tracing study of the propagation in the magnetosphere of whistler-mode VLF emissions with frequency above one half the gyrofrequency

High-frequency whistler-mode VLF emissions are excited at the equator of the magnetosphere, at frequency above one half the electron gyrofrequency and with wave normals close to the oblique resonance cone for whistler propagation. This finding has been evidenced by our measurements of wave normal directions of those waves at the equatorial and off-equatorial regions of the outer magnetosphere. The present paper deals with the propagation characteristics of high-frequency whistler-mode waves in the whole magnetosphere, by means of three-dimensional ray-tracing computations. The waves are traced, starting at the equatorial source, and the wave frequency is fixed as 0.6 times the electron gyrofrequency at the injection point. However, the initial L value is widely varied (not only outside but also inside the plasmasphere), and the initial wave normal direction is varied, but close to the oblique resonance cone. It is found that high-frequency whistler-mode VLF emissions, initially quasi-electrostatic at the equatorial source region, excited outside the plasmasphere, can propagate to a lower altitude at L ≳ 5, and then take the paths of multiple magnetospheric reflections around the equator within the plasmasphere. The characteristics of ray paths ( L value and longitude) and of the corresponding wave normal behaviour have been studied in detail, as a function of the initial azimuthal direction. Finally, the importance of these VLF emissions is discussed.

Direction finding of half‐gyrofrequency VLF emissions in the off‐equatorial region of the magnetosphere and their generation and propagation

The spectra of VLF/ELF emissions in the off‐equatorial region in the outer magnetosphere are, on occasion, found to consist of upper and lower bands with a frequency gap between them. The wave normal directions of the upper band VLF emissions have been determined by means of wave distribution function analyses based first on the measurement of three magnetic field components only, and then with the additional use of an electric field component. It is found that the wave distribution functions are composed of two peaks whose central wave normal angles θ with respect to the magnetic field at a geomagnetic latitude of ∼17° are close to the local oblique resonance cone θres but whose values of θ are always about 15°–20° less than θres at a higher latitude of ∼26°. This observed wave normal behavior is compared with the theoretical prediction from direct ray tracing studies using the hypothesis deduced from a previous investigation that the waves are generated at the equator with wave normals close to θres. A combination of this comparison and inverse ray tracing in which the initial wave normal directions are those determined from the wave distribution analysis has yielded the result that the θ values of the upper band VLF emissions are very close to θres at the equator and that the normalized frequency there, Λeq, is above 0.5. Hence the upper band VLF emissions are identified as being “half‐gyrofrequency” VLF emissions generated in the vicinity of the magnetic equator, with their wave normals close to θres. The characteristics of propagation between the equatorial source region and the observing positions have been investigated by direct ray tracing. The generation mechanism is also discussed.

On the Polarization of Half-Gyrofrequency Whistler-Mode Waves in the Two-Component Magnetospheric Plasma

Quasi-electrostatic half-gyrofrequency whistler-mode VLF emissions with wave normals close to the oblique resonance cone (θ res ) have been found to be unstable for the two-component (cold and anisotropic lower-energy hot electrons) magnetospheric plasma. The present paper deals theoretically with the electric field polarization of half-gyrofrequency whistler-mode waves in such an unstable plasma, by means of numerically solving the full dispersion relation. At wave normal angles relatively away from θ res , there exists no effect of hot electrons on the polarization. When the wave normal angle further increases above a specific value (smaller by 5–10° from θ res ) where we have wave growth, we expect the deformation of electric field polarization from that predicted by cold plasma theory; the wave becomes more transverse. The deformation becomes more pronounced for more populated hot electrons with fixed cold plasma density.

The wave normals of magnetospheric chorus emissions observed on board GEOS 2

The wave normal directions of magnetospheric chorus emissions have been analyzed by using data from the geostationary GEOS 2 satellite which is located in the equatorial region at L = 6.6. As the result of analyses for a specific day of December 19, 1979, chorus is found to be generated in conjunction with substorms and at local times from around midnight to afternoon. Two types of chorus are observed: impulsive burstlike and rising tone. The chorus during midnight to late morning hours is impulsive, and at local times from noon to dusk we notice an increase in the occurrence of rising tone chorus. The chorus spectra have shown the importance of the characteristic frequency of fH/2 (fH is the electron gyrofrequency). We notice the impulsive chorus only in the lower band (f<fH/2; f is the emission frequency) at local times from ∼0300 to ∼0700, and then at LT = ∼0800 to ∼1600 the predominant frequency of the emissions, whether impulsive or rising tone, lies in the upper band (f>fH/2) with infrequent occurrence in the lower band, and there is obviously no correlation between the elements in both bands. However, there are several intense tones which seem to be correlated in both bands for the strong two‐banded impulsive chorus emissions observed only at LT ≃ 0800. This correlation might be related with a notch in chorus risers at f ≃ fH/2 caused by Landau damping, as previously suggested. The wave normals are determined by using only the magnetic field data. The direction finding studies have been made for impulsive and rising tone chorus, separately, which have yielded different results. The lower band is discussed first. The wave normals of the rising tones having values of df/dt as normally observed are found to take very small angles (5°–20°). Then it is found that the rising tones with increased values of df/dt have shown larger wave normal angles of 30°–45°. These relatively small wave normal angles for the lower band give further support to the loss cone instability as the generation mechanism. The impulsive chorus is found to take slightly larger wave normal angles (about 5°) than most rising tones. Further, it may be suggested that different types of chorus are associated with different wave normals. Next we are concerned with the upper band chorus, whose generation mechanism is not well agreed upon. It is shown that the impulsive chorus in the upper band is generated with its wave normal close to the oblique resonance cone. This suggests that the upper band chorus is quasi‐electrostatic, and it is furthermore confirmed by the estimated ratio, c|B|/|E| (|E| and |B| are the total electric and magnetic field intensities; c is the light velocity). The rising tones in the upper band, however, have indicated a difference such that the closeness of their wave normals to the oblique resonance cone is much less distinct. An intensive comparison is made between the direction finding results for the upper band and the theoretical mechanisms so far proposed in order to elucidate the possible generation mechanism of the upper band chorus.

Further observations on resonance cones in non‐Maxwellian plasmas

Resonance cones in a hot magnetized non‐Maxwellian plasma are investigated. The non‐Maxwellian nature of the plasma is described by two electron populations: a background population and an electron beam with variable beam parameters. It is shown that the Cerenkov cone occurs at angles much smaller than the group velocity cone angle θc for the lower branch of the oblique resonance cone irrespective of the magnitude of the biasing magnetic field. When the beam velocity is sufficiently large with respect to the thermal velocity of the background electrons, a characteristic wave pattern appears outside the resonance cones. It is shown that this pattern occurs because of a propagating wave for θc ≲ θ ≲ 180°‐θc. When the beam density is low (nB ≈ 1%), the upstream resonance cone structure remains nearly unmodified, and it can be used for plasma diagnostics to deduce electron temperature and density using theoretical results based on a Maxwellian plasma.

The influence of surface stress on the shapes of ion bombarded surface asperities

In recent years considerable effort has been devoted to the observation and interpretation of microasperities which emerge on surfaces under ion bombardment. The ultimate morphologies discussed up to now have been either the right circular cone or the right pyramid. Both have been supposed essentially to owe their forms to the ion erosion process alone. In this article we examine the influence of self stress (surface tension) on morphological evolution and show that it can contribute to the development of the distorted tapered forms observed in some recent scanning electron microscopy (SEM) studies. The self stress concept is applied to a microcrystal which is assumed, for generality, to have originally had the form of an oblique cone. Cone angles and surface tension values appropriate to argon bombarded copper indicate that the stress within the ⦅111⦆ planes (i.e. the slip planes) can exceed the critical shear stress at about 1 μm or less, from the apex. Onset of deformation by slip is probable if the crystal orientation is such that there is anisotropy amongst the resolved shear stresses and the maximum resolved shear stress is aligned with the slip direction. This theory is supported by observations in which we find that cones respond to an intense ultrasonic field by bending plastically. The bent forms are identical to those reported for unvibrated cones, thus lending credence to the above interpretation of spontaneous bending.

Location of the interference structure near the lower oblique (whistler) resonance cone

By numerically solving the dispersion relation for electrostatic waves in a Maxwellian magnetoplasma with stationary ions, it is shown that above a certain frequency fα the interference structure may be either inside or outside the resonance cone, depending on the distance from the source.

The marginal fiber mass in the utricle of the pigeon

The marginal fiber mass (MFM) that Werner 26 described in the utricle ofAves was observed and analyzed in the pigeon using light, scanning electron, and transmission electron microscopic techniques. Morphologically, the MFM is a gelatinous, fibrous mass which has the shape of an oblique cone. The basal end terminates as a foot-like structure on the macula utriculi while the apical end attaches the statoconial membrane securely to the wall of the utricle. Specific tests for elastin, collagen and a ‘connective tissue type’ of reticulum indicated that none of these components were present in the MFM. The MFM did, however, stain positively with PAS, Alcian blue and a PAS-Alcian blue combination. The extent and location of the staining suggest that the main bulk of the MFM is comprised primarily of neutral mucopolysaccharides with traces of acid mucopolysaccharides on its surfaces. Based on these facts, and on other morphological observations, it is suggested that the MFM is a marginal extension of the cupular zone of the statoconial membrane which has folded back over on itself and, in the process, has sandwiched the statoconial (otolithic 7) zone between itself and the cupular zone. As a well-developed structure of the avian utricle, the MFM must be considered as a functional component in any biodynamical model of statoconial membrane displacement.

The Convex Surface of an Oblique Cone

The Convex Surface of an Oblique Cone

III.—On the Palæontology of the Selachian Genus Notidanus, Cuvier

Of the upper dental series, Probst attempts to give a tolerably complete account, but it is only illustrated by very imperfect woodcuts. Two of the foremost awl-shaped teeth are figured by Lawley (l.c. figs. 2, 3), and the same author ascribes to the upper jaw of this species three other of the Pliocene specimens. Fig. 19 represents an anterior upper tooth from the Middle Eocene of Hampshire, and the original of Fig. 20 is another from the Miocene of Baltringen, Wurtemberg. The former (B. M., p. 4707) exhibits a short thick base with an oblique principal cone, in front of which are a number of minute denticulations; posteriorly there is only one secondary cone, pointing sharply backwards, and about half the size of the principal cone; and this is followed by another small denticle. The second specimen (B. M. 35533) has also a short thick root, and shows a somewhat similar crown; the large principal cone is followed by one small secondary and a terminal denticle, and in front there are a few coarse serrations at its base.