Showing papers by "National Physical Laboratory published in 1976"
TL;DR: A new algorithm is introduced that attains efficiency by inferentially eliminating successor nodes in the tree search by means of a brute-force tree-search enumeration procedure and a parallel asynchronous logic-in-memory implementation of a vital part of the algorithm is described.
Abstract: Subgraph isomorphism can be determined by means of a brute-force tree-search enumeration procedure. In this paper a new algorithm is introduced that attains efficiency by inferentially eliminating successor nodes in the tree search. To assess the time actually taken by the new algorithm, subgraph isomorphism, clique detection, graph isomorphism, and directed graph isomorphism experiments have been carried out with random and with various nonrandom graphs. A parallel asynchronous logic-in-memory implementation of a vital part of the algorithm is also described, although this hardware has not actually been built. The hardware implementation would allow very rapid determination of isomorphism.
2,319 citations
TL;DR: In this paper, coherent axisymmetric structures in a turbulent jet are modelled as linear instability modes of the mean velocity profile, regarded as the profile of a fictitious laminar inviscid flow.
Abstract: Coherent axisymmetric structures in a turbulent jet are modelled as linear instability modes of the mean velocity profile, regarded as the profile of a, fictitious laminar inviscid flow. The usual multiple-scales expansion method is used in conjunction with a family of profiles consistent with similarity laws for the initial mixing region and approximating the profiles measured by Crow & Champagne (1971), Moore (1977) and other investigators, to deal with the effects of flow divergence. The downstream growth and approach to peak amplitude of axisymmetric wave modes with prescribed real frequency is calculated numerically, and comparisons are made with various sets of experimental data. Excellent agreement is found with the wavelength measurements of Crow & Champagne. Quantities such as the amplitude gain which depend on cumulative effects are less well predicted, though the agreement is still quite tolerable in view of the facts that this simple linear model of slowly diverging flow is being applied far outside its range of strict validity and that many of the published measurements are significantly contaminated by nonlinear effects. The predictions show that substantial variations are to be expected in such quantities as the phase speed and growth rate, according to the flow signal (velocity, pressure, etc.) measured, and that these variations depend not only on the axial measurement location but also on the cross-stream position. Trends of this kind help to explain differences in, for example, the preferred Strouhal number found by investigators using hot wires or pressure probes on the centre-line, in the mixing layer or in the near field.
430 citations
TL;DR: In this paper, the physical properties of composite materials are discussed; however, discussion of the mechanical properties has been excluded except when necessary for the consideration of properties such as thermal expansion or swelling and shrinkage.
Abstract: In this review, the physical properties of composite materials are discussed; however, discussion of the mechanical properties has been excluded except when necessary for the consideration of properties such as thermal expansion or swelling and shrinkage. One of the main aims in the review has been to show how the theoretical and experimental information that is already available may be used (a) to design and construct composite materials with predetermined physical properties and (b) to ensure that the physical properties of composite materials are properly measured and properly defined.
306 citations
01 Jun 1976-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this paper, the development of grain-refining techniques for the casting of aluminum, and the results achieved using additions of ternary Al-Ti-B master-alloys, are briefly described.
Abstract: The development of grain-refining techniques for the casting of aluminum, and the results achieved using additions of ternary Al-Ti-B master-alloys, are briefly described. A test procedure is given for assessing the relative effectiveness of these master-alloys, and the results are related to the various kinds of alloy treated, including those with constituents which “poison” the grain-refining agent. The equilibrium conditions which affect the behavior of the constituents of the grain-refined alloys are examined quantitatively from a thermodynamic viewpoint. One theory about the mechanism of nucleation of aluminum on titanium diboride is examined and found inapplicable. New data on the solubility of TiB2, ZrB2, TiC, ZrC, Cr3C2, CrB2 in liquid aluminum are presented graphically. Practical aspects of alloy behavior in grain-refining practice are analyzed and discussed on the basis of the quantitative data.
275 citations
01 Jan 1976
TL;DR: The gyromagnetic ratio of the proton in water, γ p, is a physical constant whose value is extensively used to measure magnetic fields precisely by observing precession frequencies as discussed by the authors.
Abstract: The gyromagnetic ratio of the proton in water, γ p ’ , is a physical constant whose value is extensively used to measure magnetic fields precisely by observing precession frequencies. By determining the value of γ p ’ by the weak and strong field methods we can both express in SI its magnetic fields measured in this way and realise the ampere according to its SI definition with an uncertainty of about a part in a million.
268 citations
TL;DR: In this paper, the authors describe a phenomenon in which a gratinng with very shallow grooves absorbs virtually all of the light of a given wavelength which is incident upon it.
265 citations
TL;DR: In this article, the refractive indices and optical birefringence of congruently grown lithium niobate (LiNbO3) have been measured at 0.633 μm and 3.39 μm in the temperature range 20° to 600°C.
187 citations
TL;DR: A protocol for use at the host-host level of computer networks is presented and assertions which reflect important characteristics of the protocol are derived and verified, for a demonstration that cyclic sequence numbers could be used in the protocol without ambiguity.
184 citations
TL;DR: In this paper, the results of measurements of liquid densities within the temperature range 293 to 490 K were presented for highly pure samples of n -alcohols C1 to 5, 8 and 12, and of propan-2-ol and butan 2-ol. The results were considered to have an accuracy of ± 0.15 kg m −3 over this range of temperature.
181 citations
TL;DR: In this article, the number of cavities per unit volume was a function of the shear strain and independent of the stress state, and the results are compatible with the hypothesis that cavities are produced by grain interior slip and stabilized by plastic deformation induced internal tensile stresses.
Abstract: Submicrometre grain boundary cavities are produced in Nimonic 80A when plastic deformation in any of three different stress states is followed by a short anneal. Tension, torsion and compression specimens were plastically strained in a systematic manner and then annealed for 2 h at 750 °C. Detailed quantitative observations with a 1 MV microscope showed that the number of cavities per unit volume was a function of the shear strain and independent of the stress state. Furthermore the measurements revealed the surprising result that most cavities were on those grain boundaries which were parallel to the maximum principal stress axis. However, Preferential cavity growth occurred during subsequent tensile creep and cavities on these parallel boundaries either remained constant in size or diminished while those on boundaries which were orthogonal to the applied stress axis grew relatively quickly, thus producing the usual appearance of cavitated tensile samples. Plastic strain was more detrimental to torsional creep ductility when the direction of torque between plastic deformation and creep was reversed which is in accordance with the anisotropic cavitated boundary distribution. The results are compatible with the hypothesis that cavities are produced by grain interior slip and stabilized by plastic deformation induced internal tensile stresses.
104 citations
TL;DR: In this paper, the vapour pressures of methyl propyl, isopropyl methyl, butyl methyl and decyl methyl were measured at pressures up to 205 kPa. The measured values were fitted by Antoine and by Chebyshev equations.
01 Apr 1976
TL;DR: In this paper, an open microwave resonator was used for dielectric measurements on unsintered polytetrafluoroethylene, high-density polyethylene and TPX.
Abstract: An investigation has been carried out into the use of an open microwave resonator for dielectric measurements. The resonator is of the hemispherical type and consists of one plane and one concave copper mirror. The sample is a plane parallel sheet of lateral dimensions ≥ 50 mm and is placed on the plane mirror. The theory has been extended to cover this type of resonator. Measurements on unsintered polytetrafluoroethylene, high-density polyethylene and TPX show that for materials with loss angles in the range 50–500 μrad the loss can be measured with standard deviation of ± 2% + 1μrad. The standard deviation for permittivity measurements is about ± 0.1%. A full discussion of the possible sources of error is given.
TL;DR: In this paper, the i.r. (3600-50 cm −1 ) and Raman spectra of benzonitrile in the vapour phase are reported and a vibrational assignment of the molecule is presented.
TL;DR: In this paper, the theoretical stress-strain behaviour of a three component hybrid composite consisting of a brittle fibre and a matrix composed of a binder and less brittle fibre is described, and the conditions required for a synergistic strengthening of the brittle fibres are compared for the limiting assumptions of a frictional and elastic bond.
Abstract: The theoretical stress-strain behaviour of a three component hybrid composite consisting of a brittle fibre and a “matrix” composed of a binder and less brittle fibre is described, and the conditions required for a synergistic strengthening of the brittle fibres are compared for the limiting assumptions of a frictional and elastic bond. The theory is tested using a dispersed type I carbon-glass-epoxy hybrid and it is shown that increases in effective fibre strength of around 100% can be obtained. Finally, the economic and structural advantages of using a hybrid in place of a conventional carbon composite of the same modulus are discussed.
TL;DR: In this article, complete vibrational assignments for benzaldehyde and twelve derivatives o -, m -or p - X C 6 H 4 CHO; X = F, CH 3, Cl or Br.
TL;DR: In this paper, an improved procedure for predicting noise levels L 10 from road traffic was developed for use within England and Wales in connection with the Noise Insulation Regulations 1975 and for other aspects of planning.
TL;DR: Two- and three-element combinations of hologram optical elements are considered, and analytical conditions are obtained for absence of longitudinal dispersion.
Abstract: Two- and three-element combinations of hologram optical elements are considered, and analytical conditions are obtained for absence of longitudinal dispersion. Solutions of the conditional equations are compared with another author's computed design results. A simple doublet design is considered for an eyepiece, and its performance is described.
TL;DR: Experimental work for determining the optimum composition and thickness of the coating and the applicability of the technique to substrates other than platinum are described.
Abstract: A method has been evolved for bonding aluminous porcelain to pure platinum foil used for making porcelain crowns by the conventional 'tinner's joint' technique. It was found that good bonding was achieved when the platinum was coated with 0.2-2.0 mum of tin before firing on the porcelain. This paper describes experimental work for determining the optimum composition and thickness of the coating and the applicability of the technique to substrates other than platinum.
TL;DR: In this paper, the authors used Fourier transform spectroscopy in the far infrared with a Michelson interferometer, and helium-cooled bolometric detectors, to study the emission spectrum of the stratosphere at high resolution in the spectral range 5 −45 cm−1.
Abstract: USING Fourier transform spectroscopy in the far infrared with a Michelson interferometer, and helium-cooled bolometric detectors, it is possible to study the emission spectrum of the stratosphere at high resolution (0.05 cm−1) in the spectral range 5–45 cm−1 (see refs 1–3).
TL;DR: In this paper, an improved Mach-Zehnder interferometer was used for the determination of the complex relative permittivity of liquids and low-loss solids in the frequency range v = 100 GHz to 18 THz.
Abstract: A brief outline is given of the improvements which have been made in the measurement techniques available for the determination of the complex relative permittivity of liquids and low-loss solids in the frequency range v = 100 GHz to 18 THz. These improvements involve very stable interferometric systems with either dielectric beam splitters for the upper frequency end or else free standing wire grid beam splitters for the lower frequency end, novel cell designs, the use of sensitive detectors, and of new computational procedures. The results can be checked by independent spot frequency measurements using HCN and H 2 O lasers coupled to an improved Mach-Zehnder interferometer. The optical properties of the polymeric (polyethylene, TPX, polypropylene, PTFE) and single crystal (quartz, silicon germanium) windows now assume an increased importance and we have determined refractive index n (v) and power absorption coefficient α(v) to much improved precision. With our present technique we can now determine the complex permittivity of very heavily absorbing liquids such as primary alcohols and water as far as 6 THz and beyond in favorable cases as functions of frequency over a wide temperature range.
TL;DR: In this paper, the authors compared the reproducibility of four different types of He-Ne lasers with different electronic circuits and found that the Reproducibility was affected by a modulation amplitude dependent shift of the laser frequency.
Abstract: The wavelengths of He-Ne lasers stabilized by saturated absorption in iodine and designed at BIPM, NPL, and PTB have been compared simultaneously by beat frequency measurements. The intention of the comparisons was to get experience about the reproducibility of differently designed lasers. All lasers were stabilized by third harmonic locking but with different electronic circuits. Among other effects, the reproducibility appears affected also by a modulation amplitude dependent shift of the laser frequency f. For a suitable range of modulation amplitudes the reproducibility of the four investigated lasers has been estimated to be ±4 × 10−11 f.
01 Jan 1976
TL;DR: In this paper, a quantitative theory is presented which explains how solute segregation alters grain boundary strength and explains why C, B and Be are remedial to the embrittlement of pure iron.
Abstract: A quantitative theory is presented which explains how solute segregation alters grain boundary strength. A simple treatment shows that, because of an incorrect assumption, previous theories in which segregation was thought to cause low temperature brittleness by lowering the grain boundary work of fracture are incorrect and that it is the brittle fracture stress that is altered. The decrease in grain boundary brittle fracture stress is shown to be proportional to the level of segregation and also to the excess size of the segregant atoms over those of the matrix. From the temperature dependence of the yield stress in a given alloy, it is then simple to calculate the impact transition temperature shift caused by the segregation of various species. An evaluation for the temper brittle steel, AISI 3340, gives a good numerical correlation with the published transition temperature shifts for the segregation of P, Sn, Sb, As, Si, Ge and Bi. The theory also explains why C, B and Be are remedial to the embrittlement of pure iron.
TL;DR: In this paper, it has been shown that in a manganese zinc ferrite, the initial permeability varies directly as the separation between intragranular pores and the coercive force varies inversely as the square root of this distance.
Abstract: Initial permeability and coercive force are structure sensitive properties which depend upon intragranular porosity. It has been found that in a manganese zinc ferrite the initial permeability varies directly as the separation between intragranular pores and the coercive force varies inversely as the square root of this distance. Assuming reversible motion of the domain wall pinned at the pores, the behaviour of initial permeability with respect to the distance between the pores can be adequately explained. It is not possible to give an explanation for the observed relationship between coercive force and the distance between the pores.
TL;DR: In this article, the authors used the Michelson type two beam interferometer to measure the complex refractive index (CFI) and the complex relative permittivity of medium loss as well as high loss volatile liquids over a wide temperature range (−80 °C to 80 °C).
Abstract: Dispersive Fourier transform spectrometry (DFTS) of liquids [1] in the millimetre and sub-millimetre wave region has been extended to include precise measurement of the complex refractive index ň or the complex relative permittivity e of medium loss as well as high loss volatile liquids over a wide temperature range (− 80 °C to 80 °C) by the use of variable thickness windowed cell in one active arm of the Michelson type two beam interferometer. In the past these measurements were restricted to liquids of relatively low vapour pressure because of the necessity to use a free layer of liquid. An excess of liquid vapour absorbs radiation and gives its own characteristic spectrum [2]. The free layer method and subtraction [3,4] and double subtraction [5] procedures enabled investigation of liquids of absorption coefficient a up to 250 Neper/cm. But as the absorption increases it becomes more and more difficult to produce a sufficiently thin plane parallel layer held freely under gravity. However for very absorbing liquids, like water, reflection DFTS [5,6] has been successfully used in which accurate determination of the phase shift and an extremely stable interferometric system are essential.
TL;DR: A new determination of the gas constant was made using a method in which the velocity of sound in argon was measured by means of an acoustic inteferometer operated at a temperature close to 273.16 K.
Abstract: A new determination of the gas constant has been made using a method in which the velocity of sound in argon was measured by means of an acoustic inteferometer operated at a temperature close to 273.16 K. Ninety-eight independent velocity measurements were made over a pressure range from 30 to 200 kPa to enable the velocity at zero pressure to be deduced by extrapolation. By using this experimental value, a new value for the gas constant of 8315.73 + 0.17 J K _1kmol_1 was deduced. This is higher than the old value for R , obtained from measurements of the density oi oxygen, by 159 p.p.m. (parts/106).
TL;DR: In this paper, a complete vibrational assignment of the dicyanoaurate(I) ion is presented, which is consistent with the presence of a weak Tl-Au bond.
TL;DR: In this article, the Schottky field assisted thermionic emission is the dominant conduction mechanism in the temperature range 390 to 440 K and the metalinsulator work function is calculated to ≈ 1.83 eV.
Abstract: The electrical conduction in Ag-polypropylene-Ag sandwich samples is studied measuring the dependence of current (I) on voltage (U) and temperature (T). The experimental results of I–U–T relationships show that Schottky field assisted thermionic emission is the dominant conduction mechanism in the temperature range 390 to 440 K. The metalinsulator work function is calculated to ≈ 1.83 eV. Hysteresis and polarization effects are also observed in the I–U characteristics in this range of temperature. Contribution due to bulk polarization is suggested in the conduction mechanism besides the Schottky emission.
TL;DR: In this article, various types of flowmeter used for the measurement of gas throughput in the range 10 −4 to 10 −10 Pa m 3 s −1 are described and discussed.