Arc Center Research Articles

Chatanika Radar observations of the electrostatic potential distribution of an auroral arc

Observations of a premidnight auroral arc were made with high temporal and spatial resolution, using the Chatanika incoherent scatter radar. The arc was a quiet east‐west aligned arc, about 40 km wide, that drifted slowly through the radar beam without appreciably changing in shape or luminosity. The distribution of ionospheric electric fields and currents associated with the arc were computed from the ion density and line of sight velocity. The electric field was 30 mv/m outside the arc and decreased to a few mv/m within the arc. The horizontal potential drop was only ∼ 0.6 kV across the arc. By deconvolving the electron density profiles, differential energy spectra and velocity distributions were obtained within the arc. From these the accelerating potential parallel to the magnetic field lines was estimated by several techniques. One technique makes use of an empirical relationship between the parallel potential drop and the total electron current. The accelerating potential reached 7 kV at the arc center. The parallel potential drop within the arc is combined with ionospheric electric field measurements to reconstruct the equipotential contours above the arc.

Spectroscopic investigation of a lanthanide iodide/mercury arc discharge plasma

An investigation was made of the distribution of Dy atoms and ions and iodine atoms in the central region (r/R≲0.6) of a DyI3/Hg-arc plasma. The arc is operated horizontally; it is centered magnetically. The mercury pressure is 4.5×105 N m−2, the input power 500 W, the electrode distance 37 mm, and the tube diameter is 15 mm. The temperature profile was determined from the emission of the optically thin Hg 577.0-nm line. The side-on emission distributions of optically thin Dy+ and Dy lines, in combination with the optical absorption of Dy+ resonance lines, indicate a radial depletion of dysprosium at the arc center, which can be explained by a simple model. Combination of experiments and calculations in which ambipolar diffusion is taken into account yields the distribution of Dy atoms and ions in the central region. The distribution of the iodine atoms was determined from the emission of the optically thin I 905.8-nm line. The iodine content of the arc exceeds the dysprosium content by about an order of magnitude. The chemical composition of the arc plasma is discussed. Measurements and calculations on self-reversed Dy lines also show that ambipolar diffusion is a dominant process.

Origin of arc of the Western Alps

The arc of the Western Alps started to develop during the main Alpine orogenic phase in Late Eocene to Early Oligocene time. This occurred as a side effect of the general north-south compression in the Central and Eastern Alps. Before this time no arc existed. A dominant east-west structural grain, expressed by the axes of the folds which originated during the Late Cretaceous, characterized the entire belt from the Dauphine and Provence of southeastern France to the region which later became the Eastern Alps. The final and most powerful curvature was the result of an east-southeast to west-northwest compression caused by the motion of the Italian-Dinaric microplate along the right-lateral lnsubric line during Early Oligocene to Early Miocene time. The deformation produced in the Western Alps by these movements can best be explained by applying the slip-line field theory. Accordingly, the two systems of strike-slips faults observed in the Western Alps, in the Jura mountains and in the Dauphine, are more or less parallel to the slip-lines created in the rigid plastic medium of the Western Alps by the motion of the northwestern prong of the Italian-Dinaric microplate, which acted as the indenter. It is thus postulated that by the recogniqd style of deformation the rock masses forming the arc of the Western Alps flowed toward north-northeast and south-southwest from an axis through the centre of the arc.

Spectroscopic measurements in nitrogen arcs with respect to local thermodynamic equilibrium

A wall-stabilized nitrogen arc at atmospheric pressure was studied spectroscopically in the current range from 20 to 70 A with the aim of detecting departures from LTE. Measurements of the relative intensity of several N(I) lines showed that the populations of the upper excited states are in equilibrium for currents greater than approx. 25 A. Comparisons of the excitation temperatures obtained from relative intensities with the electron temperature and with the temperature curves calculated for different departures from LTE show that deviations from equilibrium are small at the arc center for electron densities above approx. 4 × 10 16 cm -3. Deviations between the radial profiles of the electron and excitation temperatures were observed for currents between 35 and 55 A.

Radiation emission coefficients for sulfur hexafluoride arc plasmas

Calculations are made of the total spectral absorptivities of plasmas of sulfur hexafluoride for wavelengths of 100 to 15,500 Å. Both line and continuum radiation are considered. For the contributions from line radiation, we have calculated the strengths, widths and shifts of both neutral, singly and doubly ionized atoms of S and F, except that we used experimental line strengths where they are available. The theory used was that of Griem, which assumes LS coupling. Curves are given for the emission coefficient of radiation appropriate to the arc center for isothermal cylindrical plasmas of various radii for pressures of 1 and 10 atm and temperatures from 5000 to 35,000°K. It is found that at 1 atm line radiation can be an order of magnitude higher than continuum radiation and radiation >2000 Å is less than 10% of the total radiation for temperatures greater than 15,000°K. Predictions are given of volt-ampere characteristics and central temperatures for arcs of various radii in SF6 at pressures at 1 and 10 atm.

Atmospheric spreading of protons in auroral arcs

A model is developed to calculate the effect of atmospheric spreading on the flux and angular distribution of protons in homogeneous auroral arcs. An expression is derived that indicates the angular distribution in the atmosphere as a function of distance from arc center, neutral scale height, arc width, and initial angular distribution. The results of the model agree favorably with those based on Monte-Carlo calculations. From these results the enhancement factors needed to compute the original proton current above the atmosphere are obtained. A technique is indicated for determining the incident angular distribution from rocket-based measurements of the arc width and angular distribution.

Predicted Arc Properties in Sulfur Hexafluoride

Calculations of spectral absorptivities of sulfur hexafluoride for continuum radiation ranging from the far ir to 300 Å have been made as a function of temperature and pressure. These values are used together with theoretical values of thermal and electrical conductivity to derive temperature profiles of arcs in sulfur hexafluoride, taking into account effects due to self-absorption of radiation, but assuming local thermal equilibrium. The temperature profile for a 100-A arc is in good agreement with the experimental measurements of Motschmann. The sensitivity of the derived temperature profile to the input material functions is examined. It is predicted that radiation losses at the arc center are dominated by radiation of wavelengths in the region of 1000 Å. Using the theoretical material functions, an estimate is made of central arc temperatures and electric field strengths for currents of up to 60 000 A and arc radii of up to 2 cm for gas pressures of 1 and 8 atm.

Untersuchungen des thermischen gleichgewichts im wandstabilisierten ar-niederstrombogen mit N 2- und H 2-zusätzen

On a wall-stabilized Ar arc (4 mm dia., end-on observation, 4 A, 1 atm) radial temperature and electron density distributions were found by measuring intensities of band lines and atomic lines and of the Ar continuum; the gas was mixed with small quantities of N 2 and H 2. Plasma dates of the gas mixtures were computed. Temperatures, electron densities and field strengths could be explained by considering the laws of electrical and heath conduction. The electron temperature of the pure Ar arc (centre) was (1500 ± 500)°K higher than the gas temperature (extrapolation). This difference was decreasing at increasing admixtures of molecule gases; at a few percents, LTE was reached.

The effect of the plasma composition on characteristics of the d.c. arc—V: The influence of iodine vapour on the radial temperature distribution of the arc burning in the atmosphere of nitrogen and argon

Considering the solutions of the E lenbaas-H eller energy balance equation it is possible to indicate how the chemical reactions among the components of added substances influence the radial temperature distribution in the arc. In the case of addition of iodine vapour to the atmosphere of nitrogen, and argon respectively, a core of higher temperature with a larger gradient of the radial temperature distribution in the arc centre is formed. These conclusions are confirmed by experimental determinations of the radial temperature distribution.

Small-scale auroral arc distortions

Small-scale spatially periodic distortions of auroral forms have been studied utilizing low-light level television observations made at various locations in the Northern and Southern Hemispheres. The most commonly observed features were folds and vortex-like curl formations. The curls, identified here with the Kelvin-Helmholtz instability due to fluid shear, invariably had a counterclockwise rotational shape and motion when viewed in a direction anti-parallel to the Earth's magnetic field. The typical measured wavelength (∼5 km) and measured growth rate (4.2 sec −1) were used to evaluate the Kelvin-Helmholtz dispersion relation for the apparent shear ω s = ∂ ν x ∂y (28 sec −1) . The apparent horizontal velocities of both folds (0–5 km/sec) and curls (0–22 km/sec) were invariably observed to be counterclockwise with respect to the multiple arc centre when viewed antiparallel to B. Consistent agreement between rotational shape and rotational motion suggests that the apparent growth rate and the apparent horizontal velocities closely approximate the actual values. If the shear results from E×B drifts in a space charge field, the calculated value for ω s , implies an unneutralized electron density ∼0–1 cm −3 and a ΔE across the arc element ∼500mV/m. The velocity measurements indicate that the ΔE values for individual elements can combine to produce transient electric fields at the edges of multiple arcs as high as 1000 mV/m.

Mechanism of antibody diversity: germ line basis for variability.

1. S. P. 6 Ri6rdfiin and G. Daniel, New Grange (Praeger, New York, 1964). 2. G. Hawkins, Stonehenge Decoded (Doubleday, Garden City, N.Y., 1965). 3. A. Thom, Megalithic Sites in Britain (Oxford, London, 1967). 4. G. Daniel, The Megalithic Builders of Western Europe (Hutchenson, London, 1959), pp. 111-113. 5. Actually this tumulus represents what Thom calls a type D ring, one in which the two pivot stakes are placed at one-third the radius from a, rather than at the midpoint. As Fig. 3 shows, the pivots can be kept at the midpoint of the radius if a, is allowed to move inside the design. 6. L. B. Borst, Science 163, 567 (1969). 7. The monument at Borrowston Rig requires anchor points that are placed farther apart on the circumference than the intersections made by the trisecting radii demand. In this design the circle of the smaller end arc passes through the center of the larger end arc, and the wider placement of the anchor stakes may have been made on this account. The site at Maen Mawr had anchor stakes that were closer together on the circumference. If the radial line from P2 to either anchor is taken as a hypotenuse of a right triangle one side of which is half the anchor line, then the lengths of the sides of this triangle (in megalithic half-yards) are 14, 17, and 22, which is nearly Pythagorean (142+ 172= 485e 484). 8. M. Gardner, Sci. Amer. 221, 239 (1969). 9. To mention one such consequence, with the megalithic method concentric rings, such as those found at Woodhenge, can be drawn without using any special mensuration technique. That is, a rope can be lengthened by an unspecified amount and a concentric design can be drawn at once. With a flexible compass, on the other hand, the large arc in a type II egg, for example, can be drawn without special measurement but the other arcs must be changed by x amount to remain equidistant from the perimeter of the original figure. 10. Thom presents a good argument for use of a standard length of 2.72 feet (one megalithic yard) in the construction of these structures, as well as of others in both the Old World and the New. 11. The writing of this article was supported in part by the Oklahoma State University Research Foundation.

Computer calculation of two target trajectory with "centre of arc-target" stereotaxic equipment.

A method is described permitting computer calculation of a two target trajectory with “centre of arc=target” stereotaxic equipment.

Measurements of Spectral Emission and Absorption of a High Pressure Xenon Arc in the Stationary and the Flashed Modes

Concurrently with emission measurements of a high pressure xenon arc in the spectral range 3000 A to 2 micro, its absorption in the ir was measured by a technique based on modulating the less intense radiation of a carbon arc used as background source. The emission measurements were repeated with a rapid scanning spectrometer while flashing the xenon arc for 0.1 see at 10 kW, which is five times the normal power input. The arc showed excellent stability and reproducibility both in the stationary and the flashed modes. The intensity increase of the continuum was proportional to the increase of power input during the flash. A simple expression was derived connecting the spectral radiance of the continuum directly with the temperature and pressure of the arc. The temperature profile of the xenon arc was obtained using this expression and also by applying the Planck-Kirchhoff method to the Abel inverted emission and absorption of an ir xenon line. Both approaches show fair agreement at the arc center. The wavelength dependence of the correction factor for departures from hydrogenic behavior of the xenon continuum was derived from the measured spectral radiances and compared with theoretical calculations.

Zoophilic Schistosomiasis on Taiwan: Reestablishment of Schistosoma japonicum Subsequent to Drastic Alteration of Habitats by Flood

Drastic alterations in the habitats of Schistosoma japonicum in the enzootic area of Taiwan practically eliminated the parasite in the focus studied. Observations over a period of several years allowed a comparison of the status of host-parasite relationships before and after interruption of the parasite cycle by natural causes. Although excessive flooding reduced the snail (Oncomelania formosana) population and the parasite infection in definitive hosts (lower vertebrates) to near nil, Oncomelania populations returned to near normal after approximately 1 year, followed by appearance of infection in rodents. An unusual compensation in biological productivity seemed to allow for rapid reestablishment of the schistosome cycle after abnormal circumstances had placed the parasite-snail-definitive host associations in jeopardy. The inability of the Taiwan strain of Schistosoma japonicum to infect man has been a biological curiosity for years, especially since the island is geographically located near the center of a broad arc of the Orient in which schistosomiasis is a disease of great concern. Confinement to a few small areas, plus a number of other biological factors, separate the species on Taiwan from a morphologically similar parasite designated by the same name in Japan, mainland China, the Philippines, and other areas of Southeast Asia. Continuation of the cycle under adverse conditions has added to the uniqueness of the schistosome situation. S. japonicum continues to propagate itself in spite of very low biotic potentials and other uncertain circumstances relating to zoophilic schistosomiasis on the island. During the past decade Dr. H. F. Hsii and associates (1952, 1962) have elucidated the various peculiarities which differentiate the Taiwan species from others in the Far East. Their early field observations revealed the low rates of infection in Oncomelania formosana in most of the localities studied in Pu-yen Hsiang (township) near Chang-hua. Subsequent observations over a Received for publication 29 March 1965. * Research task MR. 005.09-1601.3, Bureau of Medicine and Surgery, Navy Department. This study was supported in part by funding under Public Law 480, Section 104 (c). The opinion and assertions herein are those of the author and are not to be construed as official or reflecting the views of the Navy Department or Naval Service at large. period of several years in the same area by the present author have similarly indicated rates of infection so low in the snail and lower mammalian hosts that continuation of the cycle appears all but impossible. Factors such as the seasonal reduction of infection rates in mollusks during the winter months, unpredictable drying or man-imposed alterations of snail habitats for parts of the year, intensive rodent control campaigns which eliminate a number of the infected vertebrate hosts, etc., in the enzootic areas, add to the precariousness of host-parasite associations. Hairston (1962) has presented the problems relating to population ecology and has graphically illustrated the mathematical complexities to be surmounted for maintenance of the schistosome cycle in the Philippines, where conditions, though regulated by a multitude of natural variables, probably are more favorable for parasite survival than in Taiwan. During the course of field studies, a natural disaster altered the majority of schistosome habitats and practically eliminated the infection on the west-central coastal plain of Taiwan. For approximately 1 week the S. japonicum habitats were covered as a result of flooding after excessive rains. This occurred in August (1959), the season at which parasite transmission potentials are at their height. Biological activities relating to the parasite cycle within habitats were greatly reduced and temporarily suspended as the rich, well-cultivated and irrigated, alluvial plain of Pu-yen was submerged in 2 to 6 ft of fast-flowing

Flow Regimes in Curved Subsonic Diffusers

An extension and refinement of the work of Moore and Kline (NACA TN 4080) is presented for the flow regimes found in straight-walled diffusers. A systematic map of flow regimes in curved diffusing passages is presented, in steps of ten degrees, for a range of flow turning angles from 0 to 90 degrees. Each curved diffuser geometry tested had a circular arc center line and a linear area distribution normal to the center line. The line of first appreciable stall showed a peak in divergence angle as a function of the ratio of center line length to throat width for all values of turning angle equal to, or greater than, fifty degrees. The divergence angle at the transition to the fully developed stall regime was found to decrease monotonically with increase in turning angle at fixed values of the ratio of center line length to throat width in all cases.

Pathogenesis of the acute pulmonary edema occurring after brain operation and brain trauma.

(1) By investigating many autopsy cases, it was found that the incidence of combination of the pulmonary edema was high in the cases with central nervous system diseases, particularly in the cases having localized foci in the vicinity of the internal capsule, the lentiform nucleus and the third ventricle. (2) From the histological viewpoint, an attempt was made to classify the clinical cases of postoperative acute pulmonary edema into 3 groups: (1) that occurring after a brain operation or brain trauma, (2) that occurring after a cardiopulmonary operation of cases with pulmonary circulatory disturbances, (3) that occurring after an abdominal operation of cases with metabolic disorders. It is worthy of note that the incidence of the postoperative pulmonary edema was significantly high after brain surgery. (3) In the examination of the pulmonary vascular innervation, the reflex pathway has been clarified and the 2 centers were assumed to be in the reflex arc of the innervation of the pulmonary vessels. The higher center of the reflex arc ascending through the vagus nerve was in the nuclei of the preoptic areas, while the lower center of the reflex arc ascending through the sympathetic or sinus nerve was in the medulla. The authors have also confirmed that the site of cerebral damage in the clinical cases of pulmonary edema, occurring after a brain operation or a brain trauma, had a close relation to either the higher or the lower center of the pulmonary vascular innervation or the both. (4) The authors have succeeded in the experimental production of the characteristic pulmonary edema of cerebral origin by a complete destruction of the bilateral preoptic areas. Pathophysiology concerning the experimentally produced pulmonary edema has been studied in detail. (5) Based on the results of both clinical and experimental studies, the pathogenesis of the clinical pulmonary edema occurring after a brain operation or a brain trauma was assumed to be as follows. The operation or trauma was directly responsible for the development of pulmonary hypertension, the prolongation of pulmonary circulation time, and the increase in the permeability of the pulmonary capillaries. At the same time, the operation or the trauma directly caused the changes in renal or hepatic circulation and endocrine regulation, inducing anuria, disturbance of water and electrolytes balances. The combination of these factors accelerated a selective pulmonary edema of an acute type.

The Neolithic causewayed camp at Abingdon, Berks.

The situation of the Neolithic Causewayed camp at Abingdon, discovered by the Rev. Charles Overy and made famous by the late Mr. E. T. Leeds, is well known and only requires summarizing. It lies on a spur bounded by the valleys of two brooks at the south edge of an expanse of Summertown-Radley terrace gravel, three-quarters of a mile north of the Thames. The two concentric ditches, to which reference is made below, lay between the brooks; a third similar ditch, of which pit A was possibly a section, may have lain to the south. The site was at its highest (about 202 ft. O.D.) at about the centre of arc of the outer ditch, whence there was a gentle southerly slope. The expanses of Summertown-Radley gravel in the Oxford region have been found rich in prehistoric finds, that between Radley and Abingdon being no exception.

大型歯車用簡易歯形検査機について

The authors designed a new simple involute curve tester for large spur and helical gears. This tester measures the differences between the gear tooth curve and the circular arc in the section perpendicular to the gear shaft.These differences between the true involute curve and the circular arc, and the expected errors induced by the disposition of centre of the circular arc are calculated and the range of adoption of the curve tester of this type was determined.Some records as examples were also given with the comments on them.

Convection velocity in a direct current arc

Summary The convection velocity of the gas in the centre of a vertical direct current arc has been determined by measuring the velocity of small carbon particles carried along. These sparks have been photographed with intervals of 1/250 sec. From the mean velocity of the sparks during these intervals we derived the velocity of the gas which turned out to be about 1 m/sec and to depend on the strength of the electric current and on the height abovge the lower electrode. Neither the direction of the current nor the length of the arc affect the gas velocity perceptibly.

Halo in the Zenith

AT 20 minutes to 6 P.M. on Saturday 10th inst., I witnessed a natural phenomenon which I understand is very unusual. It was a portion of a halo around the zenith. Take the zenith as centre, and with a radius of 20° describe an arc of 120° parallel to the horizon, and having 60° on each side of due west. This gives the position in the heavens, as nearly as I could determine, using no other means of observation except my eyes. The convex surface was red, concave blue. Other colours were also apparent, and were very distinct towards the centre of the arc of 120°, becoming much diluted at a greater distance. The horns of the arc gradually faded away amid the cirri with which the whole sky was covered, its blue colour being only partially obscured. You could tell at a glance that the zenith was the centre of the hale. The phenomenon only continued five minutes from the time I first saw it, until it disappeared altogether. It has been suggested to me that probably the azimuth of the sun and that of the centre of arc of 120° coincided. I think this is very likely, but I did not note it particularly at the time. The wind was easterly, and the sun shone brightly where I was standing. If any of your numerous correspondents would favour me with an explanation of the above I would be greatly obliged. No other halo or portion of a halo was visible at the time.