bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Attenuation of Spherical Shock Waves in Air
Authors: Stoner Richard G. , Bleakney Walker 
Published: January 2005

The peak pressure of spherical shock waves from small explosive charges has been determined as a function of distance by measuring the velocity of propagation and applying the velocity-pressure relation derived from the Rankine-Hugoniot equations. The charges were composed of TNT or pentolite (TNT/PETN 50/50 by weight), weighed from 1.45 to 8 lb., and were spherical or cylindrical in shape, except for one series of small rectangular blocks. Measurements on the non-spherical charges were made in the plane through the center of the charge, perpendicular to the axis.
The pressure-distance relations for the four principle charge types are given by the following fitted equations, in which Π represents excess peak pressure in atmospheres, and the distance, scaled according to charge weight, is given by the non-dimensional variable Z=R/(ρτ)⅓ where R is the distance from a charge of volume τ and specific gravity ρ:
½-lb. rectangular blocks, TNT, ΠQ=13.50/Z−769.9/Z2+36280/Z3;8-lb. cylinders, Pentolite, ΠA=10.49/Z−135.5/Z2+21070/Z3;4-lb. cylinders, TNT, ΠB=11.34/Z−185.9/Z2+19210/Z3;3.75-lb. spheres, Pentolite, ΠC=8.63/Z+295.1/Z2+7823/Z3. These equations are valid for values of Z between approximately 18 and 110. The indicated probable error of the fitted curves is of the order of one percent for intermediate distances, increasing to from two to seven percent at the extremes of the distance range covered.
The curve for spherical charges is in agreement with the Kirkwood theory, and the results for cylinders having various length/diameter ratios indicate large dependence of pressure on charge shape for values of Z up to 50 at least.
Some Observations on the Formvar Replica Method, with a Note on Glass Surfaces
Authors: Deacon Beatrice M. , Ellis S. G. , Cross W. G. , Sennett R. S. 
Published: January 2005

A study of the capabilities and limitations of the Formvar replica method has been made with more particular reference to shadow cast Formvar replicas. Observations have been made on the dependence of the deduced surface structure on the method of replication of the surface and the method of shadow casting the replica. The most suitable thickness of Formvar and evaporated metal film has been studied for various surfaces. Other replica methods have been summarized and compared with Formvar replica methods.
The structure of glass surfaces, both polished and fractured, is briefly discussed on the basis of observations made from Formvar replicas.
Pseudostructures in Electron Microscope Specimens
Authors: Watson John H. L. 
Published: January 2005

Pseudostructures, which are not real properties of electron microscope specimens but are introduced by the action of the electron beam, are described. Examples are given from samples of tetracopper calcium oxychloride, precipitates from slowly hydrolized ferric chloride solutions, and tungsten oxide to illustrate some of the effects which may occur. The polymorphism of these substances, particularly of tungsten oxide, is discussed.
The major effects which contribute to the pseudostructure formation are melting, evaporation, change of crystalline states, increase in degree of crystallinity, and migration of material. Reasons are given for concluding that the primary cause of specimen changes is to be found in the heating effect of the beam. The possibilities of secondary causes are also considered.
Artifacts may also be introduced into bacterial specimens. Observed changes in such samples are described briefly and examples are given.
The Testing of Range Finders
Authors: Gardner Irvine C. 
Published: January 2005

The errors of a range or height finder are divided, on the basis of origin, into four groups, namely: 1. External errors that originate from the lack of homogeneity in the air column between the instrument and target. 2. Instrumental errors that arise from defective performance of the instrument. 3. Physiological errors that are caused by physiological limits upon the performance of the observer's eye. 4. Psychological errors that have their origin in the psychological limitations of the ability of the observer to judge the range setting correctly.
Of these classes of errors, the designer can exert direct control, within limits, upon the instrumental errors. The three other classes cannot be controlled directly, but, given a qualitative and quantitative knowledge of their characteristics, it is possible to design a range finder or height finder in such manner as to lessen their detrimental effects. A brief discussion is given of the different known sources of error in each of the four classes, with typical values of the resulting errors as obtained by measurements made in the range-finder testing laboratory established at the National Bureau of Standards under the sponsorship of the Ordnance Department of the Army.
Statistical Factors Affecting the Intensity of X-Rays Diffracted by Crystalline Powders
Authors: Alexander Leroy , Klug Harold P. , Kummer Elizabeth 
Published: January 2005

The Laplacian probability equation can be used to predict the reproducibility of the intensities of x-rays diffracted by crystalline powders. If absorption is neglected, and N is the number of particles irradiated, p the proportion of particles which are oriented so as to diffract, and q=1 − p, the relative mean deviation to be expected in repeated intensity measurements is given by Um=0.798 (q/Np)½. When absorption and the actual distribution of particle sizes are taken into account, the expression becomes Um=0.798(qμve/pA)12,where μ is the linear absorption coefficient of the material, ve the effective volume per particle, and A the cross-sectional area of the incident beam.
The theory is confirmed by measurements on four size fractions of quartz powder using a Norelco Geiger-counter x-ray spectrometer. For typical experimental conditions and powders of medium absorbing power for x-rays, it is demonstrated that good reproducibility can be expected only if the effective particle dimension is less than approximately five microns.
Spurious Signals Caused by Noise in Triggered Circuits
Authors: Middleton David 
Published: January 2005

The expected number of peaks/sec. (nσ+N), caused by noise or by a signal and noise, in excess of a given amplitude, or triggering level, is determined for broad-band noise (a) and for the envelope of a narrow-band disturbance (b). The signals considered here are pulses of various shapes (rectangular, triangular, trapezoidal), or a carrier modulated by these pulses. The expected number of peaks per second is directly proportional to the band width of the noise, and depends in some degree (20–30 percent) on filter shape, the gaussian response yielding a larger value of nσ+N than the rectangular, for the same total input power. Further, nσ+N is greatest when the triggering level is the most probable amplitude. Pulse shape is not significant when the pulses are on only a small fraction of the total period of observation, but becomes so if (1) the time of observation is comparable to the pulse length, and (2) the pulses have sharp leading edges. The latter gives rise to a transient effect which is not ignorable. This transient contribution does not appear in the envelope of narrow-band waves, as long as the maximum time-rate of change of the wave form of the envelope is much less than the central or resonant frequency of the IF, i.e., as long as the concept of ``envelope'' is meaningful. Rectification does not change nσ+N, provided that there is no appreciable distortion of the envelope by video- or audio-filters and that the triggering level of the input is passed by the detector.
Improvement, defined in ways appropriate to the systems in question, of one circuit which can tolerate A1 spurious signals/sec. in excess of a given triggering level over another circuit, which can tolerate only A2 such signals (A1&gt;A2), is calculated for broad-band signal and noise, and for narrow-band waves following half-wave linear or quadratic rectification. In general, the improvement is slight (a few db) if the trigger levels of the two circuits are not close to the most probable value of the amplitude and if the ratio of the number of spurious signals allowed/sec. to the band width of the disturbance is small. Significant improvement follows only when the maximum tolerable number of triggering peaks/sec. is the same order of magnitude as the band width of the noise. Tables and figures illustrating the above are included in Part I; the mathematical derivations are contained in Part II.
The Absorption of Incident Quanta by Atoms as Defined by the Mass Photoelectric Absorption Coefficient and the Mass Scattering Coefficient
Authors: Victoreen John A. 
Published: January 2005

Evidence presented indicates that the absorption of quanta as defined by the mass photoelectric absorption coefficient τ/ρ and the mass scattering coefficient σ/ρ of any element may be represented by a simple expression.
Tabulated values of the calculated mass absorption coefficients μ/ρ are given for wave-lengths from 0.01 to 40 angstroms for hydrogen and carbon and from 0.01 to λK and λK to λL for aluminum, copper, tin, and lead. Graphs are given showing agreement with observed values.
The Structure of Extremely Thin Layers Evaporated in Kinetic Vacuum Systems
Authors: Stahl H. A. 
Published: January 2005

In a commercial electron diffraction camera some alkaline earth metals (from Be to Sr) or Al, Ni, or Mo were evaporated onto outgassed metal sheets or glass slides, using the starting pressure of 0.1μ of mercury. The diffraction patterns of the thinnest layers (to about 103A) presented, regardless of the evaporation speed used, the pattern of the oxide of the evaporated metal exclusively. The diffraction pattern of the metal space lattice itself was growingly observed with Be, Al, Ni, and Mo only after uninterrupted evaporation until layer thicknesses of about 1μ were reached. When Mg, Ca, and Sr were evaporated, no patterns without, at least, the most intensive oxide rings could be attained under the vacuum conditions given in the apparatus.
The results are in accord with some earlier findings of Langmuir, Beeching, Darbyshire, and Beischer, and clear up some hitherto not fully explained effects with stepwise evaporated layers. The appearance of oxide patterns is always accompanied by strong improvements of the vacuum in the evaporation compartment by the arising metal vapors, i.e., by the well-known gettering effect.
The Effect of Current Magnitude upon the Behavior of a Superconducting Bolometer in Its Transition Region
Authors: Fuson Nelson 
Published: January 2005

A simple theoretical analysis of the superconducting bolometer in transition is shown to be useful in predicting phenomena such as the shape of the transition curve and the dependence of the bolometer time constant upon the current magnitude. The analysis holds for bolometer currents smaller than a critical value which is equal to the square root of the ratio of the bolometer cooling constant to the bolometer dR/dT. For bolometers constructed in this laboratory this critical current value falls between 15 and 30 ma.
Qualitative extension of the theory to the case of large bolometer currents is made by considering the presence of regions at different temperatures within the bolometer and by summarizing the possible effects of the magnetic field due to the bolometer current upon the transition. Experimentally obtained transition curves are given for both small and large bolometer currents.
An Experimental Investigation of Formulas for the Prediction of Horn Radiator Patterns
Authors: Woonton G. A. , Hay D. R. , Vogan E. L. 
Published: January 2005

The E-plane radiation pattern has been measured at short distances and both E and H-plane patterns at relatively great distances from the mouths of several electromagnetic horns. Measured values are compared with values calculated by the Kirchhoff formula and in addition the distant patterns are compared with values calculated by the corrected formula due to Stratton and Chu.For the range of horn length and aperture considered, the Kirchhoff formula gives satisfactory agreement in the E-plane for angles as great as twenty degrees and at distances as short as one foot from the mouth of the horn; the H-plane predictions are not as satisfactory.
The Thermal Behavior of Evaporated Layers in Vacuum Devices
Authors: Stahl H. A. 
Published: January 2005

Some layers presenting the space lattice pattern of the metal (Be, Mg, Al, Mo, or Ni) were heated for constant periods. Beginning with a distinctly marked threshold temperature, the interference rings of the oxide space lattice appeared while, simultaneously, the metal space lattice pattern diminished, entirely disappearing with another higher lying temperature. The oxidation temperature ranges (for ten-minute heating periods) of Be, Mg, and Al were measured. With glucinum it is equal to that within which, Kollath stated, there was a strong increase of the emissivity of beryllium secondary emission cells.
An elementary calculation gives an inferior time limit to oxidation of the observable surface layer. The surface layer of polished metals is considered; the high secondary emissivity in the case of glucinum, together with the usually supposed Beilby layer giving only two broad diffuse diffraction rings, points to the existence of a random liquid-like network of BeO molecules on the surface of polished beryllium secondary emission cells.
Effects of Stress and Deformation on the Martensite Transformation
Authors: McReynolds Andrew W. 
Published: January 2005

The relation between elastic and plastic strains and the martensite transformation from face-centered to body-centered structure has been investigated in Fe-Ni 71–29 alloy. Transformation begins at about −30°C and is of the martensite type except that it is not all completed instantaneously but continues at decreasing rate at constant temperature.
It was found that (1) There is no anomalous decrease in elastic moduli as the Ms temperature is approached, nor is Ms affected by applied elastic stresses. (2) Plastic deformation in a temperature range above Ms causes partial transformation in amounts decreasing to zero at temperature Md≈Ms+75°C, but stabilizes against further transformation by cooling. (3) Plastic yield stress increases sharply from Md to Ms then drops suddenly to a low value just below Ms. (4) The Ms temperature depends on grain size; a factor of ten increase in grain size reduces Ms about 30°C.
These results are contrary to expectations on the basis of the usual homogeneous shear model for the transformation mechanism. They indicate that the martensite phase becomes thermodynamically stable at Md but that transformation does not begin until Ms because of surface and strain energy considerations in growth of a martensite plate from a small nucleus.
A High Temperature Precision X-Ray Camera: Some Measurements of the Thermal Coefficients of Expansion of Beryllium
Authors: Gordon Paul 
Published: January 2005

A high temperature precision x-ray camera has been designed and constructed by modification of the familiar back-reflection symmetrical focusing type of camera. The camera, specimen, and furnace are used within a vacuum chamber to avoid oxidation. The apparatus in its present form has been employed at temperatures up to 1000°C, but higher temperatures could be easily attained by making a few minor changes in the furnace materials.
The lattice parameters of beryllium have been measured up to 1000°C. The derived coefficients of thermal expansion, both linear and bulk, are presented as a function of temperature. In addition, the data present strong evidence that the hexagonal close packed form of beryllium which exists at room temperature is stable up to at least 1000°C, contrary to several reports in the literature.
Microwave Q Measurements in the Presence of Series Losses
Authors: Malter L. , Brewer G. R. 
Published: January 2005

At very high frequencies, the effect of losses in coupling devices makes itself felt in the determinations of the various Q's and of the circuit efficiency of resonant systems. It is shown that the neglect of these losses (which appear in equivalent circuits in the form of series resistance), can lead to appreciable error. Formulas are derived and curves are plotted which permit an unambiguous determination of the Q's and of the circuit efficiency when the following items are known:
1. the standing wave ratio at resonance,
2. the standing wave ratio far from resonance, and
3. knowledge as to whether the resonant system under study is ``under'' or ``overmatched'' to the external load.
Infra-Red Spectra and Structure of Hevea and Gutta Elastomers
Authors: Saunders R. A. , Smith D. C. 
Published: January 2005

The infra-red absorption spectra of the purified rubber hydrocarbon fractions of several naturally occurring elastomers (hevea, guayule, kok-saghyz, gutta-percha, balata, and chicle) have been determined at room temperature over the range 2–15μ and it has been shown that the elastomers can be classified on the basis of the spectral data as belonging to one or the other of two different types, namely the hevea type or the gutta type. Both types of elastomers have also been studied over the temperature range −25 to +80°C and reference spectra for both the amorphous and the solid (crystalline) phase(s) occurring in this range have been determined for each type. At room temperature the spectral differences between the hevea (amorphous state) and gutta (α- or β-crystalline modifications) types are much more pronounced than is the case when the spectra of both types in the same (amorphous) states are compared.
The spectra of two pair of cis-trans-isomers containing the structural unit of polyisoprene have been determined and correlated with the elastomer spectra. The results indicate but do not prove that hevea- and gutta-type elastomers have the molecular structure of cis- and trans-polyisoprene, respectively.
The infra-red absorption spectra of oriented crystalline films of hevea rubber and of gutta-percha in both the α- and β-forms have also been obtained over the range 2–15μ using polarized radiation. The observed dichroic effects lead directly to the conclusion that hevea- and gutta-type elastomers are cis- and trans-polyisoprene, respectively. Although it has not been possible to deduce the exact spacial configuration of the molecules in the crystallites, it has been indicated that the planar isoprene models are unsatisfactory and that the results are in close agreement with the twisted models proposed on the basis of x-ray diffraction.
Further use has been made of the polarization data in proposing nearly complete but tentative interpretations of the spectra of both hevea- and gutta-type elastomers. The possibility of making use of the vibrational assignments for the interpretation of spectral changes produced by oxidation or other forms of degradation is pointed out.
Effect of Surface Roughness on Rolling Friction
Authors: Bikerman J. J. 
Published: January 2005

The minimum tilt at which bearing balls roll down an inclined plate of stainless steel is greater for rough than for smooth surfaces. The roughest surfaces (finish No. 1, average height of elevations 3×10−4 cm, and finish No. 2D, average height 0.9×10−4 cm) gave an almost quantitative agreement between this height of elevations and the height of hills calculated from a theory attributing rolling friction to surface roughness. No similar agreement was observed for fine finishes, presumably because the balls used (radii between 0.159 and 0.635 cm) were too big for the irregularities on these surfaces. The elastic deformation of the surfaces in contact was irrelevant for coarse finishes. Capillary attraction presumably did not interfere as superficial drying of the system had no effect.
Surface roughness which is the cause of Coulomb's sliding friction thus seems to cause also rolling friction at low pressures.
Effective Use of Collimating Apertures in Small-Angle X-Ray Diffraction Cameras
Authors: Bolduan Orvil E. A. , Bear Richard S. 
Published: January 2005

The use of simple, aperture-collimated cameras in x-ray diffraction studies at small angles is of value in investigating the molecularly large structural features of colloidal systems, particularly when pinhole collimation is required. To make effective use of available x-radiation one must (1) consider the initial limitations imposed on a camera by the purpose for which it is to be employed, and (2) choose remaining camera dimensions so that the registering film may receive as much radiation as possible.
The initial conditions are three in number, involving the desired pattern magnification, the necessary angular or large-spacing resolution, and the requisite guarding against beam spill-over, which together essentially limit the specimen-to-film distance, the beam diameter at the film, and the diffraction area permitted to be unguarded but covered by a beam stop. Other camera dimensions are chosen so that the film center is as close to, while viewing as much of, the radiation source as possible. In accomplishing these aims it is useful to align the camera at near grazing incidence to the x-ray tube target, though there are limitations to this procedure.
Rules for systematically accomplishing the above purposes are derived herein for the extremes of symmetrical (pinhole) and unsymmetrical (slit) aperture systems, as well as for ones employing a simple class of rectangular (unsymmetrical pinhole) aperture. Criteria are also given for evaluating the relative speeds of cameras which may depart from optimum because of mechanical limitations. Finally is described the construction of a series of cameras, found useful in studying the fibrous proteins, particularly collagen, and typical diffraction patterns obtained therefrom are reproduced.
Electron Microscope and Diffraction Study of Metal Crystal Textures by Means of Thin Sections
Authors: Heidenreich R. D. 
Published: January 2005

Bethe's dynamical theory of electron diffraction in crystals is developed using the approximation of nearly free electrons and Brillouin zones.
The use of Brillouin zones in describing electron diffraction phenomena proves to be illuminating since the energy discontinuity at a zone boundary is a fundamental quantity determining the existence of a Bragg reflection. The perturbation of the energy levels at a corner of a Brillouin zone is briefly discussed and the manner in which forbidden reflections may arise at a corner pointed out. It is concluded that the kinematic theory is inadequate for interpreting electron images of crystalline films.
An electrolytic method for preparing thin metal sections for electron microscopy and diffraction is introduced and its application to the structure of cold-worked aluminum and an aluminum-copper alloy demonstrated. It is concluded that cold-worked aluminum initially consists of small, inhomogeneously strained and disoriented blocks about 200A in size. These blocks are not revealed by etching but would contribute to line broadening in the conventional diffraction experiments. By means of a reorientation of the blocks through a nucleation and growth process, larger disoriented domains about 1–3μ in size found experimentally could be accounted for. It is suggested that such a nucleation and growth reorientation phenomenon is responsible for self-recovery in cold-worked metals.
The formation of CuAl2 precipitate particles is demonstrated with both electron micrographs and diffraction patterns. A fine lamellar structure found in the quenched Al-4 percent Cu alloy is at present unexplained.