bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal properties of lobate ejecta in Syrtis Major, Mars: Implications for the mechanisms of formation
Authors: Baratoux D. , Mangold N. , Pinet P. , Costard F.
Published: April 2005

This paper reports an analysis of the thermal properties of ejecta layers of single‐ and double‐lobe impact craters on Mars. First observations of thermal properties were made at low resolution from the Phobos'88 mission and did not allow mapping of variations of thermal properties inside the ejecta layer. The THEMIS instrument on board the Mars Odyssey mission provides new high‐resolution thermal mapping of the surface of Mars. From these data we observe a systematic temperature increase at night at the edge of the ejecta. We evaluate first the possible influences on the surface temperatures at night of postimpact modification processes given the topography of an impact crater and its ejecta. We show that the observed thermal signature is more likely related to a particle size distribution inherited immediately after the impact event during the emplacement of ejecta. We propose that the kinetic sieving process, observed in experimental and natural granular flows, like pyroclastic flows, is responsible for the accumulation of larger particles at the ejecta flow front and thus is responsible for the temperature increase. Despite evidence of aeolian activity at Syrtis Major, these craters offer an example of preserved surface physical properties resulting from geological processes which have occurred since the formation of the volcanic shield of Syrtis Major. Further studies are underway with the Mars Express ongoing observations produced by the HRSC and OMEGA instruments in order to explore the interplay between the surface physical properties and the spectroscopic signatures seen at Syrtis Major.
Giant impact basins trace the ancient equator of Mars
Authors: Arkani‐Hamed Jafar
Published: April 2005

It is shown in this paper that five giant impact basins of Mars, Argyre, Hellas, Isidis, Thaumasia, and Utopia, are located on a single great circle. This suggests that the projectiles' orbital planes coincided with the equator of Mars at the time of impact. The projectiles were larger fragments of a heliocentric asteroid that broke apart as it entered the Roche limit of Mars. The mass of the asteroid was at least ∼9.8 × 1020 kg, ∼1.5 × 10−3 times the mass of Mars.
Low‐latitude ELF‐whistlers observed in Taiwan
Authors: Wang Yun‐Ching , Wang Kaiti , Su Han‐Tzong , Hsu Rue‐Ron
Published: April 2005

Detections of ELF whistler‐like events at a low latitude location are reported. Events with frequencies between 60 and 100 Hz were recorded by the ELF station at the Lulin Observatory in Taiwan from August 26, 2003 to July 13, 2004. The most distinguished feature for these events is the frequency descent in the frequency‐time spectrograms, resembling terrestrial whistlers. Other notable features include (a) a long event duration averaging up to two minutes, (b) a daytime diurnal maximum occurring around 10 am, (c) a dominant magnetic field polarization in the north‐south direction with strength of a few to tens of pT, and (d) no detection of vertical electric fields. Similar events were only reported twice for the past thirty years: one at an auroral latitude site in Alaska and the other at a mid‐latitude site in California. Possible source mechanisms including magnetosheath lion roars and lightning‐generated whistlers are discussed.
Snowpack control over the thermal offset of air and soil temperatures in eastern North Dakota
Authors: Grundstein Andrew , Todhunter Paul , Mote Thomas
Published: April 2005

The close relationship between air and ground temperatures has been used to reconstruct paleoclimate conditions from ground temperatures. Unfortunately, the presence of snow decouples air and ground temperatures and obscures their relationship. The objective of this paper is to investigate the role that snowpack conditions play in affecting the relationship between air and soil temperatures. The annual thermal offset between mean annual soil and air temperatures is examined over a 12 year period (1990–2002) at Fargo, ND, using observed soil temperatures along with simulations from a physically based snowpack model. Early season snow cover does not necessarily lead to large thermal offsets. These snowpacks, while low in density, also tended to be shallow and therefore do not provide much thermal insulation. Winter snowpacks explain a greater portion of the annual thermal offset. While denser than fall snowpacks, the extra depth and longer persistence leads to superior insulation of the ground.
Step‐wise specification of retinal stem cells during normal embryogenesis
Authors: Zaghloul Norann A. , Yan Bo , Moody Sally A.
Published: April 2005

The specification of embryonic cells to produce the retina begins at early embryonic stages as a multi‐step process that gradually restricts fate potentials. First, a subset of embryonic cells becomes competent to form retina by their lack of expression of endo‐mesoderm‐specifying genes. From these cells, a more restricted subset is biased to form retina by virtue of their close proximity to sources of bone morphogenetic protein antagonists during neural induction. During gastrulation, the definitive RSCs (retinal stem cells) are specified as the eye field by interactions with underlying mesoderm and the expression of a network of retina‐specifying genes. As the eye field is transformed into the optic vesicle and optic cup, a heterogeneous population of RPCs (retinal progenitor cells) forms to give rise to the different domains of the retina: the optic stalk, retinal pigmented epithelium and neural retina. Further diversity of RPCs appears to occur under the influences of cell—cell interactions, cytokines and combinations of regulatory genes, leading to the differentiation of a multitude of different retinal cell types. This review examines what is known about each sequential step in retinal specification during normal vertebrate development, and how that knowledge will be important to understand how RSCs might be manipulated for regenerative therapies to treat retinal diseases.
Mucin glycosylation changes in cystic fibrosis lung disease are not manifest in submucosal gland secretions
Authors: SCHULZ Benjamin L. , SLOANE Andrew J. , ROBINSON Leanne J. , SEBASTIAN Lucille T. , GLANVILLE Allan R. , SONG Yuanlin , VERKMAN Alan S. , HARRY Jenny L. , PACKER Nicolle H. , KARLSSON Niclas G.
Published: April 2005

SMG (submucosal gland) secretions are a major component of the airway surface liquid, are associated with innate immunity in the lung, and have been reported to be altered in lung disease. Changes in lung mucosal glycosylation have been reported in CF (cystic fibrosis), which may be responsible for differential bacterial binding to glycosylated components in the lung mucosa and hence increased pre-disposition to pulmonary infection. Glycoproteomic analysis was performed on SMG secretions collected from explanted bronchial tissue of subjects with severe lung disease, with and without CF, and controls without lung disease. Mucins MUC5B and MUC5AC were shown to be the dominant high-molecular-mass glycoprotein components, with a minor non-mucin glycoprotein component, gp-340, also present. Oligosaccharides containing blood-group determinants corresponding to subjects' blood type were abundant on MUC5B/MUC5AC, as were Lewis-type epitopes and their sialylated analogues, which are ligands for pathogens and leucocytes. No significant differences were found in the glycosylation of MUC5B/MUC5AC or gp-340 between CF and non-CF subjects with severe lung disease, implying that CF does not influence SMG secretion mucin glycosylation in end-stage lung disease. There were also no significant differences found in the glycosylation of these components in severe lung disease compared with non-diseased lungs. This suggests that previously reported changes in the glycosylation of respiratory glycoconjugates in CF, and other pulmonary conditions, are not due to the glycosylation of components in SMG secretions, but may involve other secretions, responses or extracellular factors.
Altered endothelial function in isolated human myometrial vessels induced by plasma from women with pre-eclampsia is not reproducible in isolated mouse vessels
Authors: MYERS Jenny , IRVINE Rachel , GILLHAM Joanna , MACLEOD Maureen , MIRES Gary , TAGGART Michael , BAKER Philip
Published: April 2005

In order to facilitate characterization of the circulating factor(s) in pre-eclampsia, the present study aimed to determine whether plasma from women with pre-eclampsia, which induces attenuated endothelial-dependent relaxation in human myometrial arteries, is also capable of inducing altered endothelial function in mouse vessels. Human vessels were isolated from myometrial biopsies taken from women with uncomplicated pregnancies (n=6). Mesenteric and uterine arteries were isolated from male, female, non-pregnant and pregnant C57B mice (n=24). Vessels were studied using a wire myograph and incubated with plasma (2%) from women with pre-eclampsia (n=12) or controls (n=12). Incubation of myometrial vessels from normal pregnant women with plasma from women with pre-eclampsia reduced endothelial-dependent relaxation. This effect was not reproduced in male or female mouse mesenteric or uterine vessels incubated with plasma from women with pre-eclampsia. In conclusion, there are species-specific differences in the actions of the circulating factor(s) on endothelial-dependent relaxation of human and mouse small arteries.
On the Diffraction of Radar Waves by a Semi-Infinite Conducting Screen
Authors: Horton C. W. , Watson R. B.
Published: April 2005

The diffraction patterns of radar waves about a semi-infinite copper screen have been measured. The measurements were made by revolving a bisectoral horn in a circle of radius 15″ or 30″ about the diffracting edge. Measurements were made at three positions along the edge, one of which coincided with the corner of the screen so that the pattern obtained was actually that of a quarter-infinite plane. Measurements were made for two orientations of the screen corresponding to angles of incidence of 0° and −22½°. Theoretical patterns have been calculated for the entire 360° of rotation and these agree well with the experimental patterns. A comparison is made between the theory, measurements, and the equivalent optical measurements.
Integrating Crystal Detectors for High Energy Photons and Particles
Authors: Alger R. S.
Published: April 2005

Three of the alkali halides, LiF, KBr, and NaCl were examined as integrating detectors for high energy photons and particles. Dosage measurements were based on the number of color centers formed in single crystals under x- and cathode-ray bombardment. Exposures of 20 to 104r (30-kv x-rays) were measured photoelectrically and 105 to 107r (3 Mev x- and cathode rays) were measured optically. The crystals have advantages in measurements where wide range, high absorption, small size, and simplicity are desirable; however, their use is restricted by the length of the bleaching period required between exposures.
Effect of a Circular Groundplane on Antenna Radiation
Authors: Leitner A. , Spence R. D.
Published: April 2005

The field of a quarter-wave-length antenna above a circular conducting disk of zero thickness—the groundplane—is calculated theoretically by use of the wave functions of the oblate spheroid. Assuming a sinusoidal distribution of current on the antenna, we compute the currents on the groundplane, the radiation resistance and the radiation pattern of the system for various values of the radius a. With these results the distortion of antenna radiation by finite groundplanes can be studied. We find good agreement with recent experimental data.
Hot-Cathode Arcs in Cesium Vapor
Authors: Steinberg Richard K.
Published: April 2005

A hot-cathode arc in cesium vapor has been studied by the use of a plane Langmuir probe to investigate the potential distribution, electron temperature and electron density in the plasma. The range of arc currents and vapor pressures over which satisfactory probe measurements may be made are determined.

In some cases it was possible to maintain the discharge with a total arc drop of less than the ionization potential of cesium (3.87 volts). Potential ``humps'' along the arc are shown to be absent, and ionization by the high energy electrons of a Maxwellian electron velocity distribution is found unsatisfactory as a possible mechanism for positive ion production in the arc. The mechanism of successive electron collisions can account for the observed ionization on the assumption that the effective lifetime in the excited state is increased by the process of the imprisonment of resonance radiation.
Allotropy of Beryllium
Authors: Sidhu S. S. , Henry C. O.
Published: April 2005

The allotropy of beryllium has been confirmed by employing different alloying properties of allotropic forms of metallic elements. Alloys of beryllium and gold, studied by x-ray diffraction methods, showed that the limit of solubility of gold in beryllium is between two and three atomic percent, and practically all of it is dissolved in the β-form. The lattice parameters of the two forms observed here are: a0=2.286A, C0=3.588A, and C0/a0=1.570 for the α-form, and a0=6.93A, C0=11.35A, and C0/a0=1.638 for the β-form. The volume of the unit cell of the β-form is about 29 times that of the α-form.
The Effect of Input Configuration on Antenna Impedance
Authors: Whinnery J. R.
Published: April 2005

It is known that the configuration of the input driving system may be of importance to the impedance of antennas at high frequencies. In this paper, a region in the vicinity of the input is considered as a transducer between the TEM mode on the driving transmission line and the spherical nearly-TEM mode on the antenna system, and the constants of this transducer are found both by calculation and measurement for a particular case. The calculation is based upon quasi-static concepts, utilizing an electrostatic field map obtained from an electrolytic tank to give the approximate form of the electric field lines. The measurement is made by finding three input reactances corresponding to the input region closed by three spun aluminum hemispheres of different radii. The three sets of data, taken at each frequency, are sufficient to determine the constants of the transducer. They are expressed here as a pi-network for comparison with calculated values.

The main portion of the antenna is analyzed substantially as in Schelkunoff's approach, with the TM modes in space and in the antenna region expressed as a shunt admittance at the end of the antenna in the TEM mode equivalent circuit. This admittance is then transformed to the desired reference on the antenna by a perturbation calculation. From there it is transformed to a desired reference on the feed line by means of the input network constants. Values calculated in this way are compared with measured values over the range 200 to 1000 mc/sec. for the particular monopoles studied. Agreement is not perfect, but appears considerably better than without consideration of the specific input configuration.
Some Crossover Properties in the Electron Immersion Objective
Authors: Jacob L.
Published: April 2005

It was earlier established that the lens field between the cathode and crossover can be represented by a simple function V=A sinhkz, so that the main properties of the paraxial ``crossover'' (or minimum section of the beam) can be determined as a first approximation in terms of ``A'' and ``k.'' The distance of the crossover works out at 8π/3k√3; its potential is A exp(8π/3√3); and the angle of the beam is simply proportional to ``k.'' The radius of the crossover is then 2/k exp[−(2π/3√3)]·tanθ for electrons of initial velocity ``A,'' where θ is the angle of emission within the paraxial limit. The differential analyzer was also used to obtain the correct solution for the trajectory equation from the field plots for different systems, and shows that the simple theory gives an adequate approximation for design purposes.
Theory of the Parallel Plane Diode
Authors: Taub A. H. , Wax Nelson
Published: April 2005

Transient and steady state solutions of the parallel plane diode are obtained. The limitations on a single valued velocity theory are investigated. These general results are applied to the space charge limited diode with the a.c. components small compared to the d.c. Power consumption is discussed and it is shown that hitherto neglected terms are of importance.
Space-Charge Effects in Electron Beams and Their Reduction by Positive Ion Trapping
Authors: Linder E. G. , Hernqvist K. G.
Published: April 2005

The spread of electron beams caused by space-charge forces is discussed. Under certain conditions ions formed from the residual gas may be trapped in the beam. An equilibrium condition may be established in which the electron and ion densities are equal, and then space-charge forces will be neutralized. Under these conditions high current densities may be produced at low voltages. A theory of ion trapping is discussed, and the equilibrium condition is formulated.

Experimental data are presented which were obtained by the application of microsecond pulses to the beam. This technique is described, and its advantages and possibilities are mentioned. Data are given on beam spread as a function of current, voltage and pressure. Data on the improvement due to ion trapping are included. An increase of current density by a factor of 30 was observed with the structures tested. Results are included on ion build-up time as a function of pressure, and on beam noise and stability in the presence of trapped ions.
Surface Waves and Their Application to Transmission Lines
Authors: Goubau Georg
Published: April 2005

In this paper the applicability of non-radiating surface waves for transmission lines is investigated. Two types of waves are considered. The first one, originally studied by A. Sommerfeld, is guided by a cylindrical conductor of finite conductivity. Although this wave type has (under comparable conditions) much lower attenuation than the waves in coaxial cables or rigid wave guides, its practical application is restricted by the fact that the extension of the field is very large. Efficient excitation and undisturbed propagation of this wave mode are feasible only for very high frequencies. The other wave type considered in this paper has not been treated in the literature. It is guided by a conductor which is coated with a dielectric layer or the surface of which is otherwise modified; for example, by being threaded. The field of this wave type has a structure similar to that of Sommerfeld's wave, but the extension of the field can be controlled by the surface modification. Thus low loss transmission lines on the basis of this wave type become feasible for frequencies above 100 megacycles. The information necessary for the design of such lines is given and the agreement between the theoretically expected transmission losses and the measured transmission losses is checked.
A Note on Control Area
Authors: Stout Thomas M.
Published: April 2005

Control area, or the integrated error for a step function input, has been used as a measure of control system performance. For systems described by θ0(s)θi(s)=e−sTd(τ1s+1)(τ2s+1)…(τms+1)(T1s+1)(T2s+1)…(Tns+1), it is proved that the control area is A=Td+ ∑ i=1n Ti− ∑ i=1mτi. A simple method of evaluation is presented and some limitations of the control area criterion are mentioned.
The Application of Rate-Process Theory to Glass. I. Breaking Strength
Authors: Hodgdon F. B. , Stuart D. A. , Bjorklund F. E.
Published: April 2005

An equation relating the ultimate strength of glass and porcelain to time under load is derived using the rate-process theory of Eyring. The data of Preston and co-workers are used to calculate the constants in the equation. The agreement between theoretical and experimental results is excellent.
Circuit Analysis of Linear Varying-Parameter Networks
Authors: Zadeh Lotfi A.
Published: April 2005

This paper describes a theory of linear varying-parameter networks which is essentially a generalization of the familiar frequency domain theory of fixed linear networks. Such basic concepts as impedance, admittance, gain, etc., are extended to linear varying-parameter networks and their important properties are outlined. Extensions are given also of the general mesh and node equations, Thevenin's theorem, dualization, and some other relations that hold in the case of fixed networks. On the whole it is shown that many theorems, properties, and relations that hold in the case of fixed networks may be extended with proper modifications to linear varying-parameter networks.
Convection Currents in Porous Media. III. Extended Theory of the Critical Gradient
Authors: Rogers F. T. , Morrison H. L.
Published: April 2005

The theory of the critical gradient for onset of thermal convection in a fluid entrapped in a porous medium is extended to allow for the exponential dependence of viscosity upon temperature and for non-linear vertical temperature-distributions which characterize transients in heat flow. Although there are approximations in the mathematical treatment, the extended theory agrees rather well with experimental data, as the simple theory does not in certain instances. New experimental data are reported for the critical gradient, obtained largely with silicone fluids in unconsolidated sands.
Theory of Axially Slitted Circular and Elliptic Cylinder Antennas
Authors: Rhodes D. R.
Published: April 2005

A method proposed by Sommerfeld for solving boundary value problems involving discontinous surfaces has been applied to the general case of a plane electromagnetic wave of arbitrary direction of incidence and polarization diffracting about one or more sections of perfecting conducting circular and elliptic cylinders of infinite length. The solution is in series form, where the series coefficients are independent for the special case of slots of infinitesimal width (slits). Radiation from the slitted cylinder is restricted to discrete right circular cones about the cylinder axis, each cone corresponding to an ordinary wave-guide mode in the cylinder, while slots of finite width radiate over a continuous range of conical angles. For slots of small but finite width, the relative pattern in the cone α=α0 about a circular cylinder of radius a is the same as in a plane normal to the axis of a cylinder of radius a sinα0; patterns of the slotted elliptic cylinder are similarly related, where the analog of radius is distance between foci. Conical patterns are shown for the principal TE and TM waveguide modes in circular cylinders containing one and two diametrically opposed axial slits.
Frequency Factor and Activation Energy for the Volume Diffusion of Metals
Authors: Dienes G. J.
Published: April 2005

The theoretical equations proposed for calculating D0 of the diffusion-constant-temperature relation D=D0e−E/RT are critically discussed in the light of presently available data. It is concluded that none of the relations gives satisfactory agreement with experiment.

Empirical analysis of experimental data covering a wide range of D0 and E values showed that the quantity E/Tm, where Tm is the melting point in °K, is the main factor in determining the value of D0, and that D0 depends approximately exponentially on E/Tm. In addition to many other diffusion constants, it is shown that the anisotropic diffusion of zinc and the widely differing diffusion constants for self-diffusion in α- and γ-iron are included in the proposed empirical correlation.

A possible theoretical basis for the empirical correlation is described based on the idea of local melting or disordering. The quantity E/Tm is identified with the entropy of activation.
Magneto-Ionic Triple Splitting of Ionospheric Waves
Authors: Rydbeck O. E. H.
Published: April 2005

In recent years reports have appeared from various ionospheric observatories concerning the appearance of a third magneto-ionic component or a so-called z trace. The phenomenon has also been called magneto-ionic triple splitting. After having recorded a number of such triple splits at the new Kiruna observatory, we became very interested in the problem as a whole. The entire matter was examined theoretically and as a result it has been possible to show that strong coupling often exists between the ordinary and z components as a critical level. It has further been possible to show that the z wave becomes strongly excited when the collisional frequency v approaches the critical collisional frequency vc of Appleton and Builder. When v is larger than vc the o echo rapidly disappears and only the z and x components remain (if vc is sufficiently small, i.e. at very high latitudes). A useful expression for the transmission coefficient of the o —z wave has been derived.
The Equivalent Circuit for the Transmission of Plane Elastic Waves through a Plate at Oblique Incidence
Authors: Thomson William T.
Published: April 2005

Equations are developed for the transmission of a plane elastic wave through a plate at oblique incidence with unequal fluid medium on each side of the plate. The plate transmitting both the dilatation and shear wave is reduced to a simple equivalent circuit with impedances which are functions of the incidence angle.
A Simple Interferometric Test for Conical Flow
Authors: Giese J. H. , Bennett F. D. , Bergdolt V. E.
Published: April 2005

In conical flows the velocity, pressure, and density do not vary on lines through the vertex of the cone. In this paper it is shown that for interferograms of general conical flows δ(y, z)/z=f(y/z), where y and z are any set of Cartesian coordinates with origin at the image of the vertex of the cone, and δ is the fringe shift at y, z. Thus, for strictly conical flow, a graph of δ(y, z)/z versus y/z should be a single curve. This suggests a test for approximate conicity that requires very little computation. This test is applied to interferograms obtained from a number of approximately axisymmetric flows at various Mach numbers about cone-cylinders in free flight. Plotted fringe shift data from the region near the nose fall into a narrow band, an indication of approximate conicity. They also closely check the corresponding theoretical fringe shift curve calculated for Taylor-Maccoll flow.
Beam Oscillations in an F-M Cyclotron
Authors: Teichmann T.
Published: April 2005

This paper considers the radial and vertical oscillations of a synchro-cyclotron beam. It is found that various oscillations of substantially constant or increasing amplitude may occur in certain regions of the field, in which there are angular or other asymmetries, though only one possible oscillation (that at n≃⅕) can occur in a field that is cylindrically and vertically symmetric. The conditions for the various oscillations, and their behavior, are discussed.
A Microwave Study of the High Pressure Arc
Authors: Cobine J. D. , Cleary E. P. , Gray W. C.
Published: April 2005

The impedance of an atmospheric pressure d.c. arc was measured at 1000 mc/sec. by means of a coaxial line and standing wave detector. The reactance and resistance of the arc, an essentially lumped load at the end of the line, increase with length of arc. The resistance decreases with increasing current and is approximately the same as the d.c. ``resistance.'' The reactance is capacitive and nearly independent of current. Air, argon, and helium were studied at currents from 1–4 amp. d.c. arc current.
A High Intensity Short Duration Spark Light Source
Authors: Fitzpatrick J. A. , Hubbard J. C. , Thaler W. J.
Published: April 2005

The spark described here provides a high intensity light source, whose effective duration approaches 10−7 second. The light intensity is nine hundred times greater than that obtained using RG8U cable cut for 10−7 second duration discharge. The cable described here is coaxial with silver conductors fired on the dielectric, a compound of barium titanate. The gain in light intensity is apparently due to both the higher capacity of the barium titanate cable and its very low characteristic impedance.
On the Radiation Patterns of Dielectric Rods of Circular Cross Section— theTM0,1 Mode
Authors: Horton C. W. , Karal F. C. , McKinney C. M.
Published: April 2005

The radiation patterns have been measured for five dielectric rods of circular cross section which were excited in the TM0,1 mode. These rods were each 0.870λ0 in diameter, and the lengths were 2λ0, 4λ0, 6λ0, 8λ0, and 10λ0. The theoretical radiation patterns have been computed by means of equivalent surface electric and magnetic currents. Excellent agreement is obtained when it is assumed that the diameter of the surface on which these currents are distributed is 0.65 of the diameter of the dielectric rod. Representative experimental and theoretical patterns are shown for the full 360°.
Plastic Flow of Platinum Wires
Authors: Carreker R. P.
Published: April 2005

The strain-time behavior of annealed platinum wires at constant stress and temperature is reported for a wide range of experimental conditions, namely: 1550 to 78°K, 900 to 40,000 p.s.i., 0.001 to 0.1 strain, 10−1 to 10−6 min.−1 strain rate.

The following relations were found to describe the results satisfactorily: σ=Aε̇n|ε,T;   σ=BepT|ε,ε̇,ε=Cta|σ,T;   Q∼logσ|ε;   ∂n∂T=∂p∂logε̇|ε,where σ=stress, ε=strain, σ=strain rate, T=absolute temperature, Q=activation energy for rate of deformation, t=time, and A, B, C, a, n, and p are constants.
The Effect of Magnetic Field on the Breakdown of Gases at Microwave Frequencies
Authors: Lax Benjamin , Allis W. P. , Brown Sanborn C.
Published: April 2005

The effect of magnetic field on the high frequency breakdown of gases has been studied. The presence of energy resonance and the modification of diffusion are shown experimentally and explained theoretically. An application is made of both the average electron theory and the Boltzmann theory, and the correspondence between these two theories is discussed.
Production of 2537 Radiation and the Role of Metastable Atoms in an Argon-Mercury Discharge
Authors: Kenty Carl
Published: April 2005

The average population of 63P1 mercury atoms is calculated from the measured 2537 output and resonance radiation diffusion theory. Average populations of 63P2, 0 are then found by comparing the absorptions of 5461, 4358, and 4047. Populations for a 0.42-amp. discharge in 3.5-mm argon of high purity plus Hg vapor at 42°C in a tube 1½ inches in diameter are for 63P2, 1, 0, respectively, 7.6×1011, 1.9×1011, and 3.5×1011 cm−3; these are ⅕, 1/20, and ⅕ of the corresponding Boltzmann populations, for the electron temperature of 11,100°K.

Rates of collisions of the first and second kinds involving electrons (average concentration 2.1×1011 cm−3), and the 61S0 and 63P2, 1, 0 states are calculated using known excitation functions and detailed balancing. The results predict populations for 63P2, 1, 0 within 10 percent of those observed; they further predict that ⅔ of the observed 2537, ⅔ of the visible triplet, and ¾ of the 3650 group are produced stepwise via 63P. Quenching collisions involving argon are assumed negligible.

The results account fairly well for the maximum in the 2537 versus Hg pressure curve, for the decrease in the 2537 output efficiency with increasing current, and for the decrease in electron temperature which is associated with both these effects.
A Dimensional Analysis of Metal Cutting
Authors: Drucker D. C. , Ekstein H.
Published: April 2005

Dimensional analysis is used in a study of the behavior of metal when it is cut. Present theories are described and some additional significant variables are found. The analysis provides a basis for the interpretation of known experimental results, and should serve as a guide for future experimental and theoretical investigations.
Interaction of a Spiral Electron Beam and a Resonant Microwave Cavity
Authors: Willenbrock F. K. , Cooke S. P.
Published: April 2005

The interaction between the electromagnetic field in a cavity and an electron beam projected along the axis of the cavity is examined. The particular cavity considered here is of the cylindrical TE11nz type in a steady axial magnetic field. If the cavity is excited in a linearly polarized mode, the electromagnetic field will drive the electrons in a helical trajectory with an expanding radius, and the electrons will excite and transfer energy to a degenerate mode oriented spatially at right angles to the driving field. In the driving plane of polarization (both planes of polarization if the cavity is excited in a circularly polarized mode), the electron beam will excite a field in phase opposition to the driving field in a manner analogous to the counter e.m.f. in an electromechanical generator. The converse case of a TE11nz cavity excited by a spiral beam of electrons is also considered.
Geometrical Factors Affecting the Contours of X-Ray Spectrometer Maxima. II. Factors Causing Broadening
Authors: Alexander Leroy
Published: April 2005

By applying Stokes' Fourier transform method for the analysis of diffraction maxima it is shown that the pure diffraction contour generated by a crystallite size distribution is apt to be approximated rather closely by the function 1/(1+k2φ2). In the case of the x-ray spectrometer this pure diffraction contour is broadened significantly by the action of the following five geometrical factors: (I) the x-ray source width, (II) flat rather than curved sample surface, (III) vertical divergence of the x-ray beam, (IV) penetration of the sample by the beam, and (V) the receiving slit width.

The broadening of the pure diffraction contour due to the action of each of the five factors and the breadth of the final contour generated by the instrument can be deduced by employing the convolution approach suggested by Spencer. The effect of each instrumental factor is expressed by a convolution equation of the form fi(φ)= ∫ −∞+∞Wi(ζ)fi−1(φ−ζ)dζ,in which φ is the angular displacement from twice the ideal Bragg angle, 2θ, fi−1 is the contour before the action of the ith geometrical factor, Wi is the form of the ith geometrical factor, and fi is the contour after the action of Wi on fi−1. Starting with a pure diffraction contour of the form 1/(1+k2φ2), generalized broadening curves are derived for the effect of each of the five geometrical factors. Using these curves it is possible to predict the breadth of the final diffraction contour generated by the spectrometer from an initial contour of any breadth.
Strain Induced Grain Boundary Migration in High Purity Aluminum
Authors: Beck Paul A. , Sperry Philip R.
Published: April 2005

A method has been developed for the study of grain boundary migration in high purity aluminum, which allows positive determination of the direction of grain boundary movements. By means of this method it was confirmed that the migration of grain boundaries resulting from surface energy takes place in the direction toward the centers of curvature of the boundaries. On the other hand, strain induced grain boundary migration, such as occurs in recrystallization, proceeds in a direction away from the centers of curvature of the moving boundaries. It was also found that certain strained grains serve as nuclei for strain-free grains of the same orientation which grow at the expense of neighboring strained grains. Most of the strain-free grains formed during the annealing of high purity aluminum cold rolled up to about 40 percent are produced by this mechanism of strain-induced boundary migration, without the formation of new nuclei.
The External Field Produced by a Slot in an Infinite Circular Cylinder
Authors: Silver Samuel , Saunders William K.
Published: April 2005

Expressions are derived for the external field produced by a slot of arbitrary shape in the wall of a circular wave guide (of infinite extent and infinite conductivity), the tangential components of the electric field in the slot being assumed to have been prescribed. This is accomplished by matching a Fourier representation of the external field, built up by superposition of basic sets of cylindrical waves, to a Fourier expansion of the prescribed field over the surface of the cylindrical wave guide. The far-zone field is obtained by applying the method of steepest descent to the Fourier integrals that constitute the coefficients in the expansion for the external field. The results satisfy the radiation conditions for far-zone fields.
A Three-Stage Electron Microscope with Stereographic Dark Field, and Electron Diffraction Capabilities
Authors: Haine M. E. , Page R. S. , Garfitt R. G.
Published: April 2005

An electron microscope is described in which a range of magnifications between 1000 and 100,000 times can be covered continuously. This is achieved through the use of an intermediate projector lens.

The principles of design are briefly discussed and the construction of the microscope and the high frequency-operated 100-kv power unit is dealt with in some detail. The instrument is provided with objective apertures to enhance image contrast and to permit operation with dark field illumination.

Data is given relating to the electron optical system and it is shown how the instrument can be used to obtain electron diffraction patterns characteristic of small areas of a specimen under microscopic observation. The alignment procedure is briefly described and some typical micrographs are shown.
A Note on Collapsing Cylindrical Shells
Authors: Sterne Theodore E.
Published: April 2005

Expressions are obtained for the instantaneous dependence of pressure upon radius within a collapsing cylindrical shell of incompressible liquid when subjected to (a) neither external nor internal pressure or to (b) an external pressure but no internal pressure. Dynamical considerations suggest that very high pressures and radial velocities should be reached.
The Theory ofNCoupled Parallel Antennas
Authors: King Ronold
Published: April 2005

The integral-equation theory of coupled antennas developed by King and Harrison, Tai and Bouwkamp for two- and three-coupled antennas is generalized to any number of units symmetrically arranged around a circle. The case of four antennas at the corners of a square is discussed in detail. Application to cage and corner-reflector antennas is indicated.

The analysis of N parallel antennas arranged in line is carried out to determine the driving voltages required to maintain specified currents. It is shown that the inverse problem cannot be carried out in general except as a problem in simultaneous integral equations, but that the special conditions obtaining for half-wave dipoles permit an approximate analysis for the currents with given voltages. This is carried through.
Immobility Phenomena and Reverse Driving Phenomena of the Electric Arc
Authors: Yamamura Sakae
Published: April 2005

When an electric arc is driven by a magnetic field, under special conditions, curious phenomena are observed. An electric arc cannot be driven by the magnetic field when it is established at very small gaps between the electrodes. Neither can it be driven by the magnetic field for the instant just after the contacts have been broken. These phenomena are called immobility phenomena. In the present work, the immobility time and the driving velocity of the electric arc were measured under various air pressures. As the air pressure decreases, the immobility time increases and the driving velocity decreases. Under a certain low air pressure, the arc cannot be driven by the magnetic field. When the air pressure is lower than this critical value, the arc can be driven again by the magnetic field; but in this case, the arc moves in a direction that is opposite to the direction of the electromagnetic force. This phenomenon is called the reverse driving phenomenon. The causes for these phenomena are considered.
Complex Stressing of Polyethylene
Authors: Hopkins I. L. , Baker W. O. , Howard J. B.
Published: April 2005

Polyethylene of such molecular weight and structure that it readily fibers or cold draws to 300–600 percent elongation by usual uniaxial, tensile stressing may react quite differently under biaxial tension. When biaxial tension in 1:1 ratio is applied to a diaphragm, some polymers show brittle fracture with <20 percent elongation at break. However, if the average molecular weight of such polyethylenes is shifted upward by crude fractionation, or an initially higher average is used, the polymers orient under complex stresses. Then, they usually elongate several hundred percent before rupture. Variations in crystallinity are also significant, although most technical polyethylene soon attains at room temperature enough crystallinity so that this factor does not cause big differences.

Although the whole study is so far preliminary, x-ray scattering of stressed samples suggests that preferred glide on certain crystallite planes tends to occur as the yield point approaches. These are such as to inhibit smooth alignment of the long chain axis in the direction of stressing. This could lead to brittleness.

Apparatus for complex stressing of sheets and tubes is described. Strains are taken from coordinates printed on the sample by the silk screen process. High speed stressing was also observed. The speed of retraction of amorphous polyethylene chains approaches that of rubber.
The Analogy between Hydraulic Jumps in Liquids and Shock Waves in Gases
Authors: Gilmore F. R. , Plesset M. S. , Crossley H. E.
Published: April 2005

The theory of the hydraulic jump is presented briefly, and the analogy between this phenomenon and the compression shock wave in gases is pointed out. The results of experimental measurements of hydraulic-jump intersections on a water table are reported. Considerable disagreement between theory and experiment is found. Other investigators have noted a disagreement between theory and experiment for compression-shock intersections in gases. The discrepancy in the aerodynamic case appears unlike that found in the hydraulic case. Possible reasons for the discrepancy in the hydraulic case are discussed; some sources of error are peculiar to hydraulic jumps and do not apply to compression shocks. Such factors limit the utility of the water table as an analog device.
D.C. Characteristics of Silicon and Germanium Point Contact Crystal Rectifiers. Part II. The Multicontact Theory
Authors: Johnson V. A. , Smith R. N. , Yearian H. J.
Published: April 2005

Part I has described the d.c. current-voltage characteristics obtained for typical Si and Ge crystal rectifiers, has given a summary of the published theories of the rectifier, and has shown that none of these theories accounts for the principal features of the observed characteristics. Part II describes the multicontact theory, an extension of the diode theory, and shows that this theory does account for the behavior of the observed characteristics. There also is described a graphical treatment, based upon the multicontact theory, which may be used in the analysis of experimental characteristics. The multicontact theory assumes that the contact potential at the metal-semiconductor surface varies from spot to spot. It is shown that an exponential distribution function for contact potentials may be used to account for the observed logarithmic slopes and that the observed temperature behavior of the characteristics may be explained by assuming that the distribution function varies with temperature in a manner dependent upon the nature of the contact.
The Cadmium Sulfide X-Ray Detector
Authors: Frerichs Rudolf
Published: April 2005

The CdS x-ray detector is compared with the photo-multiplier x-ray detector. Reduced to the same solid angle the sensitivity of the CdS x-ray detector is of the same order of magnitude as the sensitivity of the photo-multiplier x-ray detector. As the internal amplification of the primarily released electron currents in CdS is of the order 103 to 104 compared with the amplification in the multiplier tube of ½×106 the conversion process of x-ray quanta in slow electrons in CdS must be more efficient than the corresponding processes in the combination crystal phosphor screen photo-multiplier. Calibration curves show a linear relation between photo-current and intensity of x-rays at low irradiation levels. At high irradiation saturation effects occur. Oscilloscope curves of the response at 60 x-ray pulses per second are given. At strong irradiation the photo-current over a long time increases in a completely reversible way. X-ray intensities as low as 150 quanta CuKα per second are registered with a circuit employing a WL 759 trigger tube.
Mode Conversion Losses in Transmission of Circular Electric Waves through Slightly Non-Cylindrical Guides
Authors: Morgan Samuel P.
Published: April 2005

A general expression is derived for the effective attenuation of circular electric (TE01) waves owing to mode conversions in a section of wave guide whose shape deviates slightly in any specified manner from a perfect circular cylinder. Numerical predictions are in good agreement with experiment for the special case of transmission through an elliptically deformed section of pipe. The effect of random distortions in a long wave guide line is analyzed in terms of the mean-square values of the Fourier coefficients describing the distortions; and from the general formulas it appears that the mode conversion losses depend in large measure upon the statistical distribution of the various types of distortion. Under certain rather arbitrary simplifying assumptions about this distribution, it is calculated that mode conversions in a 4.732-inch copper pipe whose radius deviates by 1 mil r.m.s. from that of an average cylinder will increase the attenuation of the TE01 mode at 3.2 cm by an amount equal to 8 percent of the theoretical copper losses. The dependence on frequency of mode conversion losses in such a guide is discussed.
Wettability, a Function of the Polarizability of the Surface Ions
Authors: Sonders L. R. , Enright D. P. , Weyl W. A.
Published: April 2005

The wettability of crystals, glasses, and even of water itself can be temporarily decreased by bringing ions of high polarizability into their surfaces. Base exchange experiments are described where the hydrogen ions present in the surface layers of bentonite (a clay mineral of high exchange capacity) and of a soda-lime glass are replaced by different cations. This substitution seems to have no particular effect on the hydrophilic and rheological properties of the carriers as long as their surfaces are kept in contact with water. After drying, however, the surfaces which contain ions of high polarizability become hydrophobic, at least temporarily. A porous clay film will no longer absorb water instantaneously after having been treated with Ni2+, Mn2+, Hg2+, or similar ions with incomplete outer electron shells. Contact angles with water up to 70° could be observed for a short period for Hg2+ and Pb2+ clays.

Glass capillary tubes which have been treated with non-noble gas-type ions show a capillary rise which is much smaller than that observed with the tubes which have been treated with HCl and water only. This depression of the capillary rise, too, is temporary and can be observed only if the glass wall has been thoroughly dried previous to the experiment and if the capillary rise is measured in the upward direction.

An explanation is presented for these and allied phenomena on the basis of the polarization of ions in the strongly asymmetrical forcefields of interfaces. The experiments are correlated with the hysteresis of the contact angle and with observations concerning adhesion phenomena and catalytic activities of heavy metal ions at interfaces.
Distribution of Ionization in Materials Irradiated by Two and Three Million-Volt Cathode Rays
Authors: Trump J. G. , Wright K. A. , Clarke A. M.
Published: April 2005

Measurements are reported on the distribution of ionization in depth of aluminum produced by steady beams of two and three million-volt electrons. The variation of cathode-ray current density in a plane transverse to the beam, the effect on this transverse distribution of additional aluminum scattering foils, and a practical method of cathode-ray dosage computation are given.