Oblique Entry Research Articles

Oblique entry of a wedge into an ideal incompressible fluid

A new approach to the solution of the self-similar problem of the entry of a wedge into an ideal fluid at an arbitrary angle to the free surface is proposed. The method is based on the construction of the expressions for the complex velocity and the derivative of the complex potential in a parametric variable domain. An integral and an integro-differential equation are obtained for determining the absolute magnitude and the angle of the velocity vector at the free boundary. The calculated results for the free surface shape, the angles of contact between the free surface and the wedge, and the coefficients of the hydrodynamic forces are presented.

History, identity, and security: Producing and consuming nationalism in China

Chinese nationalism has ignited much debate among academics and the general public in both China and the West. Rather than search for the true core of Chinese nationalism, this essay will examine the curious custom of National Humiliation Day as an oblique entry into the politics of identity. The nation is not simply a question of people or territory, the author contends, but of time: the national time scripted by events such as National Humiliation Day. By comparing the differing practices of the holiday as it was celebrated in the early twentieth century and is observed in the early twenty-first century, the author argues that in the early twentieth century the political performances aimed to produce a proper Chinese nation out of the clashes between the Qing dynasty, northern warlords, and foreign empires. The goal was to construct a “China” worthy of being saved. When National Humiliation Day was revived in China at the turn of the twenty-first century, the political performances were more focused on containing the nation through a commemoration of the various crises of the early twentieth century. Thus the essay will argue that the nation does not arise from the ideology of its leaders, as much as through popular performances such as National Humiliation Day. Hence it shows how politics is best analyzed as a series of performances, not just by state actors in official sites like the Foreign Ministry, but also through the cultural governance of less official sites in art, film, literature — and public holidays. In this way, National Humiliation Day activities go beyond producing and containing nationalism; Chinese people are also consuming nationalism as part of a symbolic economy that generates identity.

Sequence stratigraphy, structural style, and age of deformation of the Malaita accretionary prism (Solomon arc–Ontong Java Plateau convergent zone)

Possibilities for the fate of oceanic plateaus at subduction zones range from complete subduction of the plateau beneath the arc to complete plateau–arc accretion and resulting collisional orogenesis. Deep penetration, multi-channel seismic reflection (MCS) data from the northern flank of the Solomon Islands reveal the sequence stratigraphy, structural style, and age of deformation of an accretionary prism formed during late Neogene (5–0 Ma) convergence between the ∼33-km-thick crust of the Ontong Java oceanic plateau and the ∼15-km-thick Solomon island arc. Correlation of MCS data with the satellite-derived, free-air gravity field defines the tectonic boundaries and internal structure of the 800-km-long, 140-km-wide accretionary prism. We name this prism the “Malaita accretionary prism” or “MAP” after Malaita, the largest and best-studied island exposure of the accretionary prism in the Solomon Islands. MCS data, gravity data, and stratigraphic correlations to islands and ODP sites on the Ontong Java Plateau (OJP) reveal that the offshore MAP is composed of folded and thrust faulted sedimentary rocks and upper crystalline crust offscraped from the Solomon the subducting Ontong Java Plateau (Pacific plate) and transferred to the Solomon arc. With the exception of an upper, sequence of Quaternary? island-derived terrigenous sediments, the deformed stratigraphy of the MAP is identical to that of the incoming Ontong Java Plateau in the North Solomon trench. We divide the MAP into four distinct, folded and thrust fault-bounded structural domains interpreted to have formed by diachronous, southeast-to-northwest, and highly oblique entry of the Ontong Java Plateau into a former trench now marked by the Kia–Kaipito–Korigole (KKK) left-lateral strike-slip fault zone along the suture between the Solomon arc and the MAP. The structural style within each of the four structural domains consists of a parallel series of three to four fault propagation folds formed by the seaward propagation of thrust faults roughly parallel to sub-horizontal layering in the upper crystalline part of the OJP. Thrust fault offsets, spacing between thrusts, and the amplitude of related fault propagation folds progressively decrease to the west in the youngest zone of active MAP accretion (Choiseul structural domain). Surficial faulting and folding in the most recently deformed, northwestern domain show active accretion of greater than 1 km of sedimentary rock and 6 km, or about 20%, of the upper crystalline part of the OJP. The eastern MAP (Malaita and Ulawa domains) underwent an earlier, similar style of partial plateau accretion. A pre-late Pliocene age of accretion (∼3.4 Ma) is constrained by an onshore and offshore major angular unconformity separating Pliocene reefal limestone and conglomerate from folded and faulted pelagic limestone of Cretaceous to Miocene age. The lower 80% of the Ontong Java Plateau crust beneath the MAP thrust decollement appears unfaulted and unfolded and is continuous with a southwestward-dipping subducted slab of presumably denser plateau material beneath most of the MAP, and is traceable to depths >200 km in the mantle beneath the Solomon Islands.

Predicting the flow field inside a close-coupled catalyst—the effect of entrance losses

A methodology is described for improving the prediction of the flow distribution in automotive close-coupled catalysts using computational fluid dynamics (CFD). Steady and pulsating flow simulations have been performed and compared with measurements obtained on an isothermal flow rig. By incorporating an extra pressure loss due to oblique entry at the monolith improved flow predictions are obtained. This work extends the methodology that has previously been developed for axisymmetric systems.

Microendoscopic Decompressive Laminotomy for the Treatment of Lumbar Stenosis

By modifying existing microendoscopic discectomy techniques, we previously developed a novel surgical treatment of lumbar stenosis and validated its ability to achieve a thorough decompression in a cadaveric study. We now describe our clinical experience with this new, minimally invasive microendoscopic decompressive laminotomy (MEDL) technique. A MEDL was performed in 25 patients with classic features of lumbar stenosis. By use of a fluoroscopically guided percutaneous technique, the working portal was docked on the lamina with minimal soft-tissue injury. With the angle of the endoscope combined with an oblique entry, a bilateral bony and ligamentous decompression was achieved under the midline, thereby preserving the supraspinous-interspinous ligaments and contralateral musculature. A second group of 25 patients treated with open decompression was used for comparison. Effective circumferential decompression was achieved in the majority of patients. The results for the MEDL group were as follows: operative time, 109 minutes per single level; blood loss, 68 ml; and postoperative stay, 42 hours. The results for the open-surgery group were as follows: operative time, 88 minutes; blood loss, 193 ml; and postoperative stay, 94 hours. The MEDL group needed significantly less narcotic medication after surgery. Overall, 16% of the MEDL patients reported resolution of their back pain, 68% improved symptomatically, and 16% remained unchanged. The outcome of the open group was very similar. Compared with an equivalent open technique, MEDL appears to offer a similar short-term clinical outcome with a significant reduction in operative blood loss, postoperative stay, and use of narcotics. This lower surgical stress, decreased tissue trauma, and quicker recovery are particularly important in this elderly population of patients.

Entry flow of a low-density-polyethylene melt into a slit die: An experimental study by laser-Doppler velocimetry

The flow behavior of a low-density-polyethylene melt in a 14:1 planar contraction was investigated by laser-Doppler velocimetry. The velocity field in the central plane of the flow channel is composed of the measurement of the velocity components in and perpendicular to the direction of extrusion. Two dies differing in their entrance angles are compared. In the case of the flat entry die large recirculating vortices are found in front of the die entry plane. Under stable flow conditions there is no material exchange between the vortices and the primary flow. It is shown that very small velocities within the vortices can be measured accurately. In the case of the oblique entry die no vortices are found. By the normalization of the velocity profiles with the average velocity in the die, calculated independently from the mass flow rate, an output-invariant presentation is found for the apparent shear rate range from 53 to 182 s−1. The velocity distribution along the centerline of the flow channel exhibits a pronounced velocity overshoot shortly after the die entry plane. The distance up to a fully developed velocity field within the die is about 15 times the height of the slit. Due to the acceleration of the melt in front of the die entry large elongational deformations occur. The resulting maximum elongation rates (20 s−1) are very high compared to those achievable by elongational rheometers. It is demonstrated by the comparison of the strain rate tensor components that the elongational deformation in the center plane of the flow channel is planar.

The question of Derrida's women

the other, in this case the question of woman (if one ignores the "but," which I will do but - only for the moment) returns the "other" to the position of object of knowledge.1 Such knowledge may be determinedly indeterminate - but indeterminacy itself can serve a purpose. Thus, the indeterminacy which Jacques Derrida ascribes to woman in his essay on Nietzsche's style, Spurs: Nietzsche's Styles/ ?perons: Les Styles de Nietzsche is often seen by his critics as yet another repositioning of woman as either the fetish of philosophy (Doane, 1989:125), or as the backdrop for the erection of a (masculine) philosophical system (See Irigaray, 1983). The beginning proper of Derrida's text is marked by a series of juxtapositions: the question of style/ the subject of woman: the question of style/veils and sails/ genres and genders/ spurs. Such an oblique entry into the question of woman allows one to overlook the ways that this essay might itself pose an interrogation of the "question of woman." If one is to examine the way that such an interrogation is articulated in the margins of this text, one must attend meticulously to Derrida's styles. One must therefore begin before the question of style2 and address the first question of his lecture: the question of the exergue. His attention in the first section of his reading to the form of the exergue will serve to situate the question of style as the question of woman. And because it is by means of an analysis of the exergue that Derrida problematizes the question of woman, I will pause at length in the space created by such an exergue.

Partial pressure gauge proposal based on a stigmatic double focusing mass spectrometer design

A substantial sensitivity improvement is predicted for partial pressure gauges using triple focusing mass spectrometer geometries. The simultaneous stigmatic and energy focusing is obtained by locating the plates of a plane condenser in the magnetic pole gap. Two ways to reach this purpose are indicated: a homogeneous magnetic field with oblique beam entry and exit or a ‘wedge’ magnet with normal field boundaries. A complete second-order ion optical description is given for both cases. Numerical values for the aberration coefficients are given for some particular cases. The resolution increase is estimated with the usual ion source parameters in a ‘wedge’ field design, compared with a stigmatic but single focusing mass spectrometer the main path radius being the same.

Three-dimensional problem for entry of a disk into a compressible liquid

The unsteady problem for the oblique entry of a disk into water is solved. The water is assumed a perfect compressible liquid and the flow is assumed adiabatic. The flow and state parameters are determined during the numerical integration of the system of nonlinear equations which describe the given flow by means of a three-dimensional finite-difference scheme [1]. The variation in time of the drag coefficient as a function of the Mach number and the angles of entry and attack, the pressure distribution and the shape of the free surface formed behind the disk are investigated. The oblique entry of a disk into water and its subsequent motion have mainly been studied for velocities at which the compressibility of the water is negligible [2–4]. The influence of compressibility on the duration of the rise time and the impact load was investigated experimentally in the range of Mach numbers 0 < M0 <−0.3 [5]. Semiempirical dependences are obtained for the maximum of the drag coefficient and its rise time.

Wedge entry into initially calm water

This paper presents results of calculations based on the Cauchy's theorem method of Vinje and Brevig 1 for the two-dimensional entry of wedges of various angles into initially calm water. The problem has a long history which is briefly reviewed in the introduction, and significant progress has been made with both linear theories (valid for low entry speed) and with theories which treat the free surface conditions exactly but with the assumptions of zero gravity and constant speed of entry. This simplifies the problem to one which is self-similar in dimensionless space variables ξ = x/vt and η = y/vt and this has a number of consequences. For wedges with half-angles up to about 45° and with high entry speeds, the numerical approach, which includes gravity, validates these assumptions and the agreement between both free surface displacements and pressure distributions on the wetted wedge surface is excellent except in the region of the jet of fluid which rises up the side of the wedge. Because the potential flow initial value problem is singular at the intersection of the free surface and wedge surface, exact numerical resolution of the jet is not possible. Nevertheless, the rest of the fluid motion is insensitive to the treatment of the jet, which itself may be calculated quite realistically. Of particular interest (but little practical relevance) is the pressure on the upper part of the wedge surface (in the jet region) which according to self-similar theories is very small but positive, but which is calculated to be small but negative by the numerical scheme. This effect, which is enhanced when gravity is included, is insensitive to the numerical resolution of the jet and suggests that the jet may separate from the wedge surface, the new intersection point being where the pressure vanishes on the wedge surface. A modified numerical scheme allows this to happen and the results are in qualitative agreement with the experiments by Greenhow and Lin. 2 The numerical method presented here is extremely versatile and a number of other effects may be explored. Examples of transient motion, non-constant speed of entry, oblique entry and complete penetration of the surface so that a cavity is formed behind the wedge are presented.

Oblique Water Entry and Exit of a Fully Ventilated Foil

The oblique entry of a two-dimensional, fully ventilated foil into a horizontal layer of water of arbitrary thickness is considered. When the thickness of the layer is finite, exit of the foil from the layer is studied. The present work is an extension of a previous one,2 in which only vertical entry and exit of the foil were considered. The consideration of oblique entry makes the present solution useful in studying not only the advance ratio effect on a partially submerged supercavitating propeller but also many other problems, such as the high-speed water entry and exit of a wing or a control surface, the operation of a high-speed hydrofoil in a high sea state. The results obtained in this work indicate that the force and moment coefficients of a foil decrease as the advance ratio is reduced.

Oblique entry of a slender body in an incompressible fluid

The plane problem of oblique penetration of a slender semiinfinite body in an ideal, weightless, and incompressible fluid is examined. Detailed numerical computations are performed for a wedge with rectilinear sides. The formulas obtained are applicable also for the calculation of the hydrodynamic reactions during emergence of a body from a fluid or during transverse motion of a half-blunt body with a low relative velocity. Moreover, the results of the present paper can be used to evaluate the hydrodynamic forces acting on underwater wings or propeller blades during intersection with a free surface.

The Use of a Ureteric Nipple Alone for Reflux prevention

In the re-implantation of a ureter into the bladder, vesico-ureteric reflux can be prevented by a ureteric nipple alone, provided the nipple is at least 1.5 cm long. This eliminates the need for an oblique ureteric entry or a submucosal tunnel. Longer nipples may be used although they may lead to difficulties with catheterisation. Reduction in the length of the nipple frequently occurs later.

Transfer matrices of the magnetic wedge field sectors

The second order radial and first order axial transfer matrices of actual magnetic wedge field sectors are derived. The fringing field, boundary curvature, oblique beam entry and exit effects are included.

E-vector sensitivity patterns in the goldfish optic tectum

1. Spike responses of single optic tectal units to plane polarized light have been recorded with extracellular electrodes in the goldfish. Responses to a series of eight 500 msec flashes were summed and the quantitative effects ofe-vector direction studied over 4–5 log units of intensity with white light and narrow spectral bands of equal quantal content at 460, 540 and 620 nm. 2. As previously reported all or nearly all tectal cells tested (115) were sensitive to the direction of the stimulus' polarization plane. Control experiments with a thin high order birefringent retarder next to the cornea and acting as a pseudo depolarizer provided further proof that thee-vector discrimination found in the optic tectum (as well as the previously reported oriented behavior to polarized light in fish) depends on an intraocular analyzer. 3. Systematic study of tectal cells has been made at various depths and in all directly accessible areas. No localized or differential effects of recording depth one-vector discrimination have been found. However, both directions of maximum response and degree of polarized light sensitivity (PLS) show distinctive patterns over the tectal area. 4. On the basis of established tectal projection maps these data show that preferred retinale-vector directions are tangentially arranged around the eye axis when the stimulus is axial. Distribution of this angular sensitivity seems continuous without discrete channels favoring particular polarization planes. 5. Sensitivity (determined from intensity response curves) is minimal in the center of the retina for an axial stimulus and increases peripherally out to 50–60° or more off axis. Sensitivity ratios of 4–6 are common and much larger ones have been occasionally recorded. 6. Shifting the direction of stimulus from axial to 45° and 60° upward from the axis proved that retinal patterns of preferrede-vector directions and sensitivities are symmetrical relative to the beam axis rather than the anatomical eye axis. Therefore individual tectal cells and before them their retinal receptor elements show different directions ofe-vector preference and different PLS ratios depending on the stimulus configuration. 7. Intensity response curves determined with the red, green and blue narrow spectral bands were essentially superimposable. Therefore, we have no evidence that there is any special interaction of λ and PLS. 8. The effects of stimulus intensity and retinal adaptation on the IR curves do not indicate any particular selective effects. Substantial polarized light sensitivity was present in both the light adapted and dark adapted state. PLS ratios in various cases were (1) about the same at different intensity levels or (2) greater at low than high intensities or (3) greater at high than low intensities. 9. We conclude that linearly polarized light evokes a large entoptic image in the goldfish eye. Two opposite light sectors perpendicular to thee-vector alternate with two dark sectors parallel to thee-vector. Both Haidinger's brushes and Boehm's brushes in human vision show some similarities but also some important differences. The goldfish PL image is achromatic, weak or absent axially and strong peripherally. Also the contrast between the sectors does not depend on movement of the stimulus on the retina to prevent fading as it does in both of the other phenomena. 10. The most likely mechanism for the observed PLS in the goldfish eye is either differential scattering intraocularly or oblique entry of light into the receptor outer segments. Yet present data prevent a firm choice between them.

A general purpose method for computer generation of isodose contours from external X-ray sources with applications to treatment planning

A method has been developed for the generation of isodose contours from external 60Co sources which requires as input only sources to skin distance (SSD), field size (FS), trimmer setting, apparent source width and a field size dependent attenuation coefficient M. Fields are calculated directly, at any grid size and normalization desired, allowing continuous variation of beam-defining parameters. The penumbra is successfully approximated, and central axis data are within 3% of data tabulated at different SSD and FS. The same accuracy applies in the calculation of central axis data for X-rays in the energy range 2-31 MeV; thus, quite general applicability is indicated for many types of photon beams. Running time is about 5 s per symmetric 10*10 field on moderate computers. In this paper, a brief description of the method was presented, emphasis being placed subsequently on its application to treatment planning situations involving (1) split fields, (2) wedged fields, (3) oblique entry and (4) multiple ports, by making the coefficient M a function of position for a given FS. Finally, comparisons were made with hand-calculated results for multiple port, wedged field therapy in certain head and neck cases.

Dose Distribution in Conical Rotation Therapy at 2 MeV

Various moving-field therapy technics have been developed with a view to achieving optimum dosage distribution for particular patient needs. Conical rotation therapy, in which the patient lies on a horizontal rotating cot under a fixed inclined beam, was first developed for units operating at 200-250 kV and later extended to 2 MeV radiations from a Van de Graaff generator, at the Royal Cancer Hospital in London, by Wheatley, Steed, et al. (1953). In order to preserve the skin-sparing effect with this quality of radiation, the London group did not use a surface wax cone to counteract the otherwise oblique entry of the beam, but aimed the beam axis deep to the lesion, so that the zone of maximum dosage lay around the lesion center, whether one- or two-sided irradiations were delivered. This entails the use of a relatively broad beam in relation to the treatment volume, and the steep angle of entry tends to raise the exit dose. In consequence, the percentage depth dose and rate of fall of dosage outside the ...