Equivalent Velocities Research Articles

Electron Capture by Protons and Deuterons

Cross section measurements are reported for electron capture into the 3s state by 20-150 keV protons and deuterons incident on molecular hydrogen and deuterium. Conventional wisdom indicates that these cross sections should be nearly identical at equivalent velocities and researchers routinely use deuteron projectiles to extend proton excitation curves downward in velocity. This practice has been questioned on theoretical grounds and some investigators have reported consistent differences in cross sections for the two isotopes, however, nearly always within the experimental uncertainty of the measurements. We have made a systematic study of the 3s electron capture cross sections described above to check for isotopic effects. These cross sections are then compared to previous measurements reported in the literature.

Local characterization of free-field ground motion and effects of wave passage

abstractA simple model of the seismic source and of the propagation medium is used to obtain a local representation of the free-field ground motion in terms of a small number of equivalent dispersive plane waves. Numerical values for the equivalent phase velocities entering in the representation are presented for different epicentral distances and source depths. Based on the local characterization of the free-field motion, estimates of the magnitude of the effects of nonvertically incident seismic waves on the response of foundations and structures are presented.

Correlation of field injuries and GM hybrid III dummy responses for lap-shoulder belt restraint.

Simulated frontal, lap-shoulder belted, barrier impact tests were performed using a Volvo sedan and General Motors Hybrid III anthropomorphic test dummy. Swedish field accident injury data for this vehicle are available from another published study. For the purpose of this program, the injuries were logically subdivided into four body regions: head, neck, thorax, and lower torso. The Hybrid III has instrumentation in each of these regions. The results of three replicated tests at barrier equivalent velocities of nominally 32 and 48 km/h are discussed in terms of the field injuries, thereby providing a basis for more intelligent interpretation of future Hybrid III test results.

Analysis and Testing of Powered Tillage Blades

ABSTRACT FUNDAMENTAL design considerations for powered rotary tillage blades are presented and discussed. The relationship between blade angular velocity and the geometric dimensions of cutting edges is specified for tillage blades rotating counter to the direction of travel and assuming a typical forward speed for tillage. Analyses showed that a powered blade rotated op-posite to the direction of travel can be operated at relatively lower angular velocities than can one rotated in the direction of travel to achieve equivalent blade velocity and acceleration relative to the soil. Furthermore, a blade rotated opposite to the direction of travel requires relatively lower power to achieve equivalent blade velocities relative to the soil. Experiments revealed that, in order to minimize power requirements, the ratio of the tangential velocity of cutting edges on a blade divided by the ground speed should be as low as possible as long as a proper tillage action is obtained.

A velocity profiler based on the principles of geomagnetic induction

Abstract A technique to determine the variations of horizontal velocity between the sea surface and bottom, based on the measurement of electric currents generated by the motion of the seawater through the Earth's magnetic field, has been developed. A freely-falling Electro-Magnetic Velocity Profiler, EMVP, senses the currents as a function of depth. Velocity is inferred as the equivalent velocities required to generate the observed electric currents in the local geomagnetic field. The inferred velocity profile is relative to an unknown, but depth-independent, velocity contribution. Hence, the profiles are of the depth-variable velocity components. The device is released from the surface, falls to a preset depth or to the sea floor and returns to the surface. Both descent and ascent take about 90 min in water 6000 m deep. The r.m.s. velocity errors are about 1 to 2 cm s−1 at the vertical resolution of independent methods, 50 m and larger. Simultaneous profiles by two identical EMVPs have r.m.s. velocity differences of less than 0.7 cm s−1 at a vertical resolution of 10 m. A second electric measurement on the instrument yields a velocity profile within 0.3 cm s−1 r.m.s. of the first electric measurement every 10 m. A performance level of ±1 cm s−1 at a vertical resolution of 10 m is indicated. This level is expected in the absence of strong magnetotelluric currents, which can produce errors as large as 10 cm s−1 during infrequent (10 to 20 times per year) periods of strong temporal fluctuations of the geomagnetic field. Temperature, electrical conductivity, pressure, and other variables are recorded twice each second. The digitally recorded data are processed aboard ship to obtain velocity and density profiles.

Ionization and charge transfer in fast H+-He+collisions using an intersecting beam technique

A fast intersecting beam technique has been used to obtain total cross sections sigma (He2+) for He2+ formation from the combined processes H++He+ to H++He2++e (ionization) and H++He+ to H+He2+ (charge transfer) in the centre-of-mass energy range 72-402 keV. At these energies, ionization is believed to provide the main contribution to the measured cross sections which are shown to be in good agreement with cross sections for ionization predicted theoretically by scaling data for H+-H collisions. Values of sigma (He2+) also show the expected tendency to converge to corresponding cross sections for ionization by electron impact at high equivalent velocities.

Maintenance of the F-region at night: Incoherent scatter measurements at a mid-latitude station

Observations of F-region plasma densities and temperatures made with the pulsed incoherent scatter radar at Malvern (52.1°N, 2.3°W) during six equinox and winter nights between October 1968 and October 1970 are presented. Two separate periods of apparent influx of plasma can be distinguished, one before and one after magnetic conjugate point (MCP) sunrise. The first influx period was seen on five nights and the second on two nights. In all except one case, hydrostatic equilibrium appears to have been preserved within the errors of measurement. By comparing the observed heat input to the electron gas with that expected if the apparent flux is due to in situ ionisation by precipitating 200 eV electrons, it is found that for some periods part of the flux could be due to precipitation, but in other cases an influx of thermal plasma must be occurring. The equivalent vertical drift velocities required at great heights to produce the observed fluxes by diffusion from the exosphere seem anomalously large, especially for the post-MCP flux. It is suggested that when a plasma flux occurs, north-south horizontal transport caused by an east-west electric field is at least as probable a source as vertical transport by diffusion.

Mineralogy, Correlation, and Grain-Size Distributions of Mazama Tephra and Other Postglacial Pyroclastic Layers, Pacific Northwest

Mazama air-fall tephra is a pumiceous pyroclastic deposit dispersed over almost a million square kilometers by an eruption about 7,000 yr ago of ancient Mount Mazama, the precursor of Crater Lake caldera, Oregon. The tephra layer is valuable as a stratigraphic marker and for what it reveals about the production and dispersal of tephra. The tephra is characterized by its minerals, which include plagioclase (73.1 ± 1.2 percent), hypersthene (9.4 ± 0.5 percent), magnetite (10.2 ± 1.1 percent), hornblende (3.9 ± 0.4 percent), and clinopyroxene (2.8 ± 0.3 percent). Mean refractive index of glass is 1.508 ± 0.001. Mineral abundances and refractive index are homogeneous, and over the region sampled the variances of these properties are no greater than in a single fragment of pumice. Within about 300 km of Crater Lake, the abundance of discrete mineral grains increases, but the proportion of heavy minerals does not change with increasing distance. Tephra at 14 localities can be correlated with Mazama tephra mineralogically. The localities are at Blue Mountains, Columbia Gorge, and China Hat Butte in Oregon; Curelom Cirque in Utah; and at archaeologic sites at Fort Rock Cave, Paisley Cave, Connley Cave, Three Sheep Rockshelter, Everyone, Hobo Cave, Wildcat Canyon, and Big Eddy in Oregon; and Night-fire Island in California. Other tephra layers in the region studied contain assemblages of minerals similar to the Mazama assemblage, perhaps because all have sources among volcanoes of the Cascade Range. This makes discrimination difficult, and no layers could be definitively correlated or identified with a specific source. Mazama tephra has heterogeneous size-frequency distributions that fit Rosin9s distribution. Heterogeneity is caused by intermingling of coarse pumiceous fragments and finer crystalline grains; however, if grain size is expressed as terminal velocity, then frequency distributions are log-normal and homogeneous; grains of disparate size or density occur together because they have equivalent terminal velocities. Phi median diameter varies curvilinearly with distance from Crater Lake, but the relation is not readily interpreted in terms of mechanism of deposition. Median terminal velocity, however, varies as V t * = K 3 · D − r , where V t * is median terminal velocity and D is distance. The parameters K 3 and r may characterize individual eruptions and facilitate understanding of the production and dispersal of air-fall tephra.

Experimental Study of Heavy Mineral Segregation Under Alluvial Flow Conditions: ABSTRACT

In order to understand local alluvial flow sorting processes of grains of different densities, studies were made of 4 bed configurations in a large recirculating flume. These bed configurations included flat beds, End_Page 331------------------------------ transition flow beds, and 2 kinds of dune beds. Bed material used in the study was a moderately well sorted sand (median = 0.286 mm) from the Rio Grande near Bernardo, New Mexico. Opaque heavy minerals consisting mainly of ilmenite and magnetite (median = 0.144 mm) made up 0.38% of the bed material by volume. Concentrations of opaque heavy minerals were formed as 3 basic types: (1) small thin concentrations associated with dunes that lacked topset beds and on the stoss sides of large dunes with topset beds; (2) concentrations associated with the topset deposits of large dunes and with dunes formed in the transition flow; and (3) widespread concentrations associated with the flat-bed condition. The most important factors influencing the type and degree of sorting of the opaque heavy minerals from light minerals were bed configuration and grain density. The thickest deposits of heavy minerals were associated with the topset deposits of large dunes, but the most widespread deposits were associated with the flatbed type of bed form. Density is important to segregation because the differences in shear stress necessary to move the light minerals and to move opaque heavy minerals are large. Equivalent fall velocities of grains of two different densities were determined to have little importance in local segregating mechanisms. End_of_Article - Last_Page 332------------

Análisis del comportamiento espectroscópico de largo período de las estrellas Be

Las estrellas Be son objetos tempranos con líneas en emisión que muestran variabilidad espectroscópica en diversas escalas de tiempo asociadas con diferentes fenómenos que tienen lugar en sus envolturas extendidas. La complejidad de estos objetos hace que aún estén en debate las condiciones físicas y dinámicas del material circumestelar que los rodea. Con el fin de aportar información acerca de la estructura y evolución de las envolturas extendidas de las estrellas Be, analizamos las variaciones espectroscópicas de dos objetos Be, 48 Lib y 66 Oph, cuya compleja fenomenología resulta difícil de ser explicada por los modelos de envoltura existentes. Para nuestro análisis utilizamos material recopilado de la literatura y espectros obtenidos en CASLEO. Estudiamos, en particular, el comportamiento de la línea H del hidrógeno, cuyo perfil resulta sensible a los cambios físicos ocurridos en la envoltura. Describimos, para ambos objetos, las variaciones temporales cíclicas de largo período de los valores medidos de velocidades radiales, anchos equivalentes e intensidades del ala roja y el ala violeta del perfil de H. En lo que respecta a 48 Lib, completamos el análisis del material espectroscópico que ya había sido publicado por Áreas y Cidale en 2006, agregando nuevos datos. Para 66 Oph observamos que la intensidad de la emisión en la línea Há comienza a decaer en 1996 indicando una dilución de la envoltura y el comienzo de un fase B normal. Cabe destacar la importancia de continuar con un seguimiento temporal de este objeto para detectar el inicio de una nueva fase de actividad estelar. Palabras Clave: estrellas variables; envoltura circumestelar; línea de emisión DOI: http://dx.doi.org/10.5377/rct.v0i4.529 Revista Ciencia y Tecnología, No. 4, Segunda época, Junio 2009: 90-98

Fallout 137Cs: Direct aerial transfer as an important source of foliar deposition

A 4 acre stand of alfalfa was systematically sampled and analyzed for 137Cs during the 1965 growing season. In addition, the deposition of fallout 137Cs in rainfall and surface air concentrations were measured. A small section of the field was covered to exclude fallout deposition by rainfall. The 137Cs in alfalfa in the open field increased during rainless periods, while during the rainy periods the alfalfa levels often decreased. While the levels in the open field were higher than under the shelter, the differences were not great enough to indicate that deposition from rainfall was a primary factor in the contamination of alfalfa in the normal environment. Overall deposition velocities for transfer of surface air 137Cs to vegetation were calculated by neglecting the possibility of contamination for rain, but considering the exponential decay-rate of deposited 137Cs. Overall deposition velocities were calculated for transfer of surface air 137Cs to vegetation without regard for deposition from rain in the open field and compared with the deposition velocities calculated for the covered alfalfa. For a first cutting of alfalfa, which grew from late May through July, the deposition velocities were 920 and 690 m/day, for unsheltered and sheltered alfalfa, respectively. The equivalent deposition velocities for a second harvest were 260 and 310 m/day for unsheltered and sheltered alfalfa.

Lyman-Alpha Emission Cross Sections forH2+andD2+Collisions with the Rare Gases

Cross sections for the emission of Lyman-alpha radiation resulting from ${\mathrm{H}}_{2}^{+}$-and ${\mathrm{D}}_{2}^{+}$-rare-gas collisions have been measured in the energy range from 1 to 25 keV. Excited states of the H or D atoms which decay via the $2p\ensuremath{-}1s$ Lyman-alpha transition result from charge transfer to antibonding states of the ${\mathrm{H}}_{2}$ or ${\mathrm{D}}_{2}$ molecules or from direct excitation to antibonding states of the molecular-ion projectiles. The ${\mathrm{D}}_{2}^{+}$ cross sections are similar to those for ${\mathrm{H}}_{2}^{+}$ when plotted at equivalent projectile velocities. The results are compared with earlier measurements of the Lyman-alpha emission cross sections resulting from ${\mathrm{H}}^{+}$ and ${\mathrm{D}}^{+}$ collisions with rare gases and with the total charge-transfer cross sections for the ${\mathrm{H}}_{2}^{+}$-rare-gas systems.

Space System Specific Impulse

Abstract : The system specific impulse (Iss) was determined to be the equivalent of specific impulse (Isp) of an idealized system having the same net effectiveness as the actual system but with zero mass of all structural equipment except the payload. THE Iss for chemical and nuclear propelled launch vehicles is compared on the basis of specific impulse, structural factors, equivalent velocities, and number of stages. With Iss, it is possible to separate the system net effectiveness of a multistage vehicle from the downgrading of payload-carrying capabilities introduced by the staging and to recognize that the system effectiveness for each stage is proportionate, or that it is a simple summation if the staging is non-proportionate.

Experimental search for the effect of compressibility in unsteady Couette flow

Solution of the compressible Rayleigh problem involving an impulsively moved flat plate indicates that transverse velocities can be generated by a purely longitudinal shearing motion. It would be desirable to demonstrate the existence of these waves, and to do so was the motivation for the present investigation. However, the geometry for the Rayleigh problem is prohibitive; and since it was noticed that a similar behaviour should occur for the case of unsteady compressible Couette flow, this was considered for the present investigation. An experimental search for the existence of the transverse velocities was conducted using concentric rotating cylinders to generate the flow. Since these transverse velocities were too small to be measured directly, a temperature gradient was created across the annulus to take advantage of the much greater sensitivity of a hot-wire to temperature fluctuations produced by the fluctuation in the transverse velocity. The periodic temperature fluctuations noted were converted to equivalent transverse velocities. Experimental values obtained agreed qualitatively with the theory. Finally, the role of extraneous effects in the experimental apparatus was considered.

Meteorology for All: Being some Weather Problems Explained

THE science of the weather may well make a wider appeal than any other branch of science, and the opening for a book which is not only scientifically accurate, but also simple and easily comprehended, is therefore very great. The author of the present work has realised that the opening exists, and has endeavoured to fill it, but his attempt can scarcely be considered successful. A few quotations will illustrate the nature of the book. In estimating cloud amounts on the scale 0-10 we are told that "if there is one cloud upon the horizon or in any part of the sky we put 1."For obtaining true bearings from a compass, “the magnetic variation in the British Isles is now 14°W.” Again: “There is no more sure precursor of a gale than the ‘wind-dog,’ or coloured parhelion” (p. 2), which may possess some degree of truth, but scarcely seems compatible with: “When these halos are coloured and accompanied by parhelia or mock suns, they generlly precede very dry weather” (p. 110). Even in such a simple matter as giving the equivalent velocities of the Beaufort numbers, the author falls into error. Some chapters are better than others, but the book can certainly not be recommended as a safe guide to put into the hands of the non-technical reader without previous knowledge of meteorology. Meteorology for All: Being some Weather Problems Explained. Dr. Donald W. Horner By. With an Introduction by M. de Carle S. Salter. Pp. xvi + 184 + vii plates. (London: Witherby and Co., 1919.) Price 6s. net.