Function Of Particle Velocity Research Articles

Two-stage temperature rise in a thermoviscoplastic half-plane under impact

A thermoviscoplastic constitutive model is used to treat uniaxial shock wave propagation in a material exhibiting rate-sensitive plasticity and thermal softening. Simple relations are obtained for the pressure jump as a function of the density jump, shock speed as a function of particle velocity, and pressure decay behind the shock front. Also, the model predicts a two-stage temperature rise, involving a jump at the shock front followed by a rise due to plastic dissipation (stress decay). The temperature rise and other quantities are predicted in the case of impact of titanium plates.

Silt‐clay aggregates on Mars

Viking observations suggest abundant silt and clay particles on Mars. It is proposed that some of these particles agglomerate to form sand size aggregates that are redeposited as sandlike features such as drifts and dunes. Although the binding for the aggregates could include salt cementation or other mechanisms, electrostatic bonding is considered to be a primary force holding the aggregates together. Various laboratory experiments conducted since the 19th century, and as reported here for simulated Martian conditions, show that both the magnitude and sign of electrical charges on windblown particles are functions of particle velocity, shape and composition, atmospheric pressure, atmospheric composition, and other factors. Electrical charges have been measured for saltating particles in the wind tunnel and in the field, on the surfaces of sand dunes, and within dust clouds on earth. Similar, and perhaps even greater, charges are proposed to occur on Mars, which could form aggregates of silt and clay size particles. Electrification is proposed to occur within Martian dust clouds, generating siltclay aggregates which would settle to the surface where they may be deposited in the form of sandlike structures. By analog, siltclay dunes are known in many parts of the earth where siltclay aggregates were transported by saltation and deposited as ‘sand.’ In these structures the binding forces were later destroyed, and the particles reassumed the physical properties of silt and clay, but the sandlike bedding structure within the ‘dunes’ was preserved. The bedding observed in drifts at the Viking landing site is suggested to result from a similar process involving siltclay aggregates on Mars.

XII.—The Hexapole Magnet as a Velocity Selector and Polarizer for Neutral Spin-½ Particles

SynopsisThe general paraxial particle-optic properties of the hexapole field are summarized and lens formulae derived. Formulae are given for the transmission as a function of particle velocity and system geometry for geometries appropriate to the case of neutral atom beams and of slow neutron beams respectively. These formulae are used to evaluate the hexapole magnet as a velocity selector and polarizer for atomic beams and as a spin polarizer for neutron beams. Some experimental observations on potassium beams are quoted in support of the theory.

A study of low-energy galactic cosmic rays from 1961 to 1965

The results from a series of balloon flights beginning in 1961 and ending in 1965 are presented. Measurements of the cosmic-ray intensity were made using a dE/dx and E detector sensitive to energies from 15 to 80 Mev/nucleon. Proton and helium intensities at 85 Mev/nucleon are presented for the five-year period covered by the balloon flight series. The behavior of the proton to helium ratio as a function of time is discussed within the framework of Parker's model for the solar modulation of cosmic rays. In 1965 a modified version of the dE/dx and E detector with an extended energy range was flown for the first time. A cosmic-ray helium spectrum from 60 to 500 Mev/nucleon measured by this detector is presented. The change in proton and helium intensities as a function of particle velocity in this energy region from 1963 to 1965 is examined and compared with the results predicted by the various special cases of Parker's model.

Ionization Probability of Iron Particles at Meteoric Velocities

The number of ion pairs produced by the total ablation of iron particles in air and argon was measured as a function of particle velocity. Micron-size iron particles of known mass and velocity were injected into a gas target chamber and the resulting ionization collected with a parallel-plate ionization chamber. Initial velocities of the particles ranged from 20 km/sec to 45 km/sec. The probability of ionization, , for an iron particle in argon was found to be p = 2.75 X 13, where 2' is the particle velocity in meters per second. The probability of ionization of an iron particle in air was found to be p = 2.60 X 10- 2' 12, with V in meters per second.

The average charge of stripped heavy ions

Charge distributions were measured of 10–70 MeV S−, As−, I− and U-ions after passage through different gas and foil strippers. An empirical expression for the average equilibrium ionization as a function of particle velocity, nucleat charge and stripper properties is given.

The flux of the cosmic ray hydrogen and helium nuclei at Kiruna, Sweden

The results of measurements made at balloon altitudes at locations with nominal geomagnetic threshold rigidities of 0.5 GV and 2.5 GV are presented. Data have been obtained on the differential energy spectra of primary hydrogen and helium nuclei in 1964 at a time close to solar minimum, using a combined scintillator and seintillator-cerenkov technique. These data are compared with the results obtained with similar equipment which was flown at the same locations in 1961 and 1962, and also with those of other investigators. The solar modulation of the primary cosmic ray beam is examined as a function of particle velocity and rigidity and the implications of the measurements are briefly discussed in connection with the interaction of galactic cosmic radiation with the interplanetary environment.

Density of Particle Tracks in the Hydrogen Bubble Chamber

Measurements have been made of the density of charged-particle tracks in the Brookhaven 20-in. hydrogen bubble chamber as a function of particle velocity and chamber operating conditions. The track density m is given by the function A (Ps)nβ−2 where, at 27°K, A=7.5×10−8 bubbles/cm of track, n=5.4, and Ps is the superheat pressure in psia in the chamber. The pressure superheat dependence Δm/(mΔPs)≅10% per psia; for tracks at different temperatures but with the same pressure superheat, the temperature dependence Δm/(mΔT) is in the range 5–15% per 0.1°K, over the region of normal chamber operation. Macroscopic bubbles grow at the rate 0.21 mm msec−½, until they are quenched by chamber recompression in proportion to their degree of internal energy. The measured track density dependencies are consistent with the view that bubbles originate on stopped secondary electrons produced in close collision processes, where distant collision influence is suppressed by the density effect much more for hydrogen than for the heavier bubble chamber liquids. It is shown that formation and growth of bubbles to critical size may be understood in terms of conventional fluid dynamics provided the expansion is extremely rapid. The secondary electron energies required for bubble formation at 27°K range from 80 to 292 eV depending on the superheat of the chamber.