Showing papers by "National Physical Laboratory published in 1995"
TL;DR: Practical and reliable methods of measuring quality of use have been developed by the MUSiC project and these provide criteria for usability which can be incorporated into a quality system.
Abstract: The conventional assumption that quality is an attribute of a product is misleading, as the attributes required for quality will depend on how the product is used. Quality of use is therefore defined as the extent to which a product satisfies stated and implied needs when used under stated conditions. Quality of use can be used to measure usability as the extent to which specific goals can be achieved with effectiveness, efficiency and satisfaction by specified users carrying out specified tasks in specified environments. Practical and reliable methods of measuring quality of use have been developed by the MUSiC project. These provide criteria for usability which can be incorporated into a quality system. A description is given of the MUSiC methods for specifying the context of use and measuring effectiveness, efficiency, and satisfaction.
474 citations
TL;DR: In this article, it was shown that the depth resolution in ARXPS is limited by signal-to-noise ratio, not the number of emission angles for which data is acquired, and that depth resolution can be improved by up to a factor of about 2 by confining the interval over which the CDP is reconstructed.
306 citations
TL;DR: It is suggested that quality of use should be the major design objective for an interactive product and user-based evaluation can be used to validate achievement of these requirements.
Abstract: Publisher Summary This chapter discusses the distinction between broad and narrow approaches to usability and identifies the broad approach to usability with the higher level quality objective of quality of use. It is suggested that quality of use should be the major design objective for an interactive product. This relates usability to business objectives and elevates usability from an optional extra to the prime design goal. The narrow approach is complementary and is concerned with the design of features of the product that are a pre-requisite for quality of use. The two different interpretations of usability lead to two approaches to the specification and evaluation of usability. The chapter describes that user-based evaluation can be used to validate achievement of these requirements. Usability attributes provide a contribution to achieving quality of use. The presence or absence of these attributes can be verified early in design. In addition, frequent user-based evaluation of early mock-ups and prototypes is required to give feedback on the quality of use of potential solutions.
190 citations
TL;DR: In this paper, a SiC coating was developed for the protection of carbon-carbon composites against oxidation at temperatures up to 1700 °C, provided that the cracks that developed in the SiC coatings due to mismatch of thermal expansion of SiC and carbon carbon composite were filled with a sealant based on boron.
111 citations
TL;DR: In this paper, it was shown that these materials are structurally inhomogeneous at a molecular level, in which In 2 Se 3 microclusters are dispersed in the Ge-Se matrix.
Abstract: Bulk glasses of Ge-Se-In have been prepared by quenching the melt and have been subjected to thermal crystallization and X-ray structure analysis of devitrified materials. These glasses show a transformation from a single-stage to a double-stage crystallization with respect to composition. The present investigations indicate that these materials are structurally inhomogeneous at a molecular level, in which In 2 Se 3 microclusters are dispersed in the Ge-Se matrix. These results are discussed using the chemical threshold in glasses.
95 citations
01 Dec 1995-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: A 3He sandwich spectrometer incorporating two semiconductor detectors and a proportional counter region has been designed and constructed to perform high resolution measurements of neutron energy spectra in the energy range 100 keV to 15 MeV as discussed by the authors.
Abstract: A 3He sandwich spectrometer incorporating two semiconductor detectors and a proportional counter region has been designed and constructed to perform high resolution measurements of neutron energy spectra in the energy range 100 keV to 15 MeV. The efficiency of the spectrometer was determined experimentally, using a 252Cf spontaneous fission source, in the low-scatter facility of the National Physical Laboratory. The Monte Carlo technique was also used to determine the efficiency and these calculated values were used to extrapolate the measured efficiency to higher energies. The neutron energy spectra from two different sized Am Be neutron sources and an Am B neutron source were measured. Although these spectra have been measured previously, the present work represents an improvement in the energy resolution and extends the energy range. Average values for dose equivalent quantities for neutrons from these sources are also presented. The spectral data is available from the authors, as a printed table or on a computer diskette, on request.
95 citations
TL;DR: This chapter presents human-computer interaction (HCI) standards, which broadly fall into two categories—one is a top-down approach, which is concerned with usability as a broad quality objective: the ability to use a product for its intended purpose and the other is a product-oriented bottom-up view.
Abstract: Publisher Summary This chapter presents human-computer interaction (HCI) standards. Standard user interfaces provide the benefit of consistency; they become out of date as technology changes, and are usually only appropriate for limited types of users and tasks. Thus most work on international standards for HCI has not been about precise specification, but instead has concentrated on the principles that need to be applied in order to produce an interface, which meets user and task needs. These standards broadly fall into two categories—one is a top-down approach, which is concerned with usability as a broad quality objective: the ability to use a product for its intended purpose. The other is a product-oriented bottom-up view, which is concerned with aspects of the interface that make a system easier to use. The broad quality view originates from human factors, and standards of this type are applicable in the broad context of design and quality objectives. The product-oriented view concentrates on the design of specific attributes, and relates more closely to the needs of the interface designer and the role of usability in software engineering.
94 citations
TL;DR: In this article, a mixture of tetraethoxysilane (TEOS), methyltriethoxynitrile (MTES), TEOS and MTES were hydrolysed in the presence of phenolic resin, ethylcellulose, polyacrylonitrile, PAN and starch to incorporate the gel into the carbon source in the silica network.
Abstract: Silicon carbide (SiC) was synthesised from silicon alkoxides and various carbon sources. Tetraethoxysilane (TEOS), methyltriethoxysilane (MTES) and a mixture of TEOS and MTES were hydrolysed in the presence of phenolic resin, ethylcellulose, polyacrylonitrile (PAN) and starch to incorporate the gel into the carbon source in the silica network. The gel thus obtained was carbonized at 800°C in an argon atmosphere to obtain the mixture of silica and carbon which when heated to 1550°C in argon yielded silicon carbide. The characterization of the product by X-ray, FTIR and SEM showed it to be β SiC with different crystallite and grain sizes. The difference in the crystallite and grain sizes is attributed to the nature of the carbon source. The density of the SiC obtained by the sol—gel process was found to be lower than the values reported for SiC and this is ascribed to the porous nature of the products generally obtained by this process.
80 citations
TL;DR: In this article, a system for the calibration of the intensity/energy response function for electron spectrometers used in AES and X-ray photoelectron spectroscopy (XPS) is described.
67 citations
TL;DR: In this article, the PANI-LB-GOX enzyme was entrapped between the layers of the Langmuir-Blodgett (LB) film and the immobilized GOX was tested for retention of its catalytic activity and its ability to perform like a reagentless glucose biosensor.
65 citations
TL;DR: In this paper, a review of several models for predicting hardness and magnetic properties from grain sizes is presented, and it is shown that there is a need for standardisation of the grain size measurement method before agreement can be reached on the most appropriate empirical equation.
Abstract: The interest in hardmetals with fine grain sizes derives from an understanding that hardness generally increases with a decrease in WC grain size. WC powders with very fine sizes are increasingly becoming available. The use of non-standard terms for these materials can be confusing and benefits could accrue from a rationalisation of the terminology for their description. Their use is also putting new demands on the requirements for testing and characterisation of sintered structures. These issues are considered in detail in this paper together with a review of several models for predicting hardness and magnetic properties from grain sizes. For example, the use of the Hall-Petch model for predicting the relation between the grain size and hardness of hardmetals is discussed. The model appears to be satisfactory for the range of materials currently commercially available. However, extrapolation beyond that range will require some care. Coercivity measurements provide an indirect method for estimating grain size. There are a number of empirical equations available in the literature relating coercivity to grain size. These are also critically examined and it is shown that there is a need for standardisation of the grain size measurement method before agreement can be reached on the most appropriate empirical equation.
TL;DR: In this paper, rain water samples were collected at New Delhi during the monsoon of 1994 at a height of 30 m above the ground level using a wet-only collector and bulk samples from two different heights at 30 m and 13 m were collected.
Abstract: Rain water samples were collected at New Delhi during the monsoon of 1994 at a height of 30 m above the ground level using a wet-only collector. Simultaneously, bulk samples from two different heights at 30 m and 13 m were collected. Frequency distribution of pH in wet-only samples revealed that rain was mostly alkaline Four out of 23 events were observed to be acidic where the ratio of (Ca+Mg+NH4)/(SO4+NO3) was very low. pH and ionic constituents were higher in bulk samples than in wet-only samples. On an average, the concentration in bulk samples at 30m height exceeded the wet-only samples by 13% while bulk samples collected at 13m height had 19% higher concentration than the bulk samples at 30m height and 32% higher than wet-only. The acidity of ram water was mainly contributed by sulphuric acid rather than nitric acid. At the height of 30 m, the acidity was primarily neutralized by NH4 while at 13 m height, it was buffered by Ca and Mg indicating the influence of dust particles.
TL;DR: In this paper, the results of unlubricated sliding wear tests carried out on ceramics and composites based on silicon nitride were described and compared from room temperature to 1200°C.
TL;DR: The polymer electrolyte films obtained by the addition of silver thiocyanate to polyethylene oxide have been investigated by complex impedance spectroscopy, X-ray diffraction, FTIR, optical microscopy and transference number measurement techniques as discussed by the authors.
TL;DR: In this article, the creep behavior of polymers depends on the physical age of the material at the time of stress application, and the creep curve shifts to longer times for more highly aged material and, in poly(vinyl chloride), (PVC), this can be modeled by an empirical equation in which the magnitude of an effective mean retardation time parameter is dependent upon, and increases with, the age of a polymer.
Abstract: The creep behavior of polymers depends on the physical age of the material at the time of stress application. Creep curves shift to longer times for more highly aged material and, in poly(vinyl chloride), (PVC), this can be modeled by an empirical equation in which the magnitude of an effective mean retardation time parameter is dependent upon, and increases with, the age of the polymer. Creep compliances for PVC also depend on the magnitude of the applied stress when this exceeds about 4 MPa. This nonlinear behavior is caused, at short creep times, by a reduction in the value for the retardation time parameter on application of the creep stress. Specimens appear therefore to be initially de-aged by elevated stresses. Subsequently, this parameter increases with creep time implying that physical aging has been reactivated, but the rate of increase also depends on the stress level. These influences of elevated stresses can be described by an extension of the creep model, and parametric expressions have been derived which relate creep compliance values to time, stress, and the age of the polymer. It is shown how the parameters can be determined from a short series of creep experiments and thus how creep deformations can be calculated over wide ranges of time, stress, and age.
TL;DR: In this article, high pressure phase transformations of amorphous boron nitride (aBN) to cubic Boron Nitride (cBN) using magnesium B 2 B 2 N 4 ) as a catalyst-solvent were described.
TL;DR: In this paper, the degree of spectral coherence (μ12(ω)) over the plane of a double slit is determined from the measurement of spectral changes in Young's interference experiment using the spectral interference law.
Abstract: The degree of spectral coherence (μ12(ω)) over the plane of a double slit is determined from the measurement of spectral changes in Young's interference experiment using the spectral interference law. The experimental and theoretically calculated values of μ12(ω)) for the experimental parameters agree well within experimental error, thus supporting the theoretical prediction of D. F. V. James and E. Wolf (1991, Phys. Lett. A, 157 6). The degree of spectral coherence determined is used for estimating the intensity distribution across a source. This new approach, being a simple spectral measurement technique, might find its application in astronomy, particularly for the study of intensity distribution across stars.
TL;DR: In this paper, the preparation of homogeneous single-phase ZnSe films using a two-stage selenization process is demonstrated, and the films are optically transparent and have an optical band gap of 2.65 ± 0.05 eV, confirming the formation of the wide band gap semiconductor.
TL;DR: Carbon-carbon composites have been developed using Panex fibers (oxidised PAN fibers) possessing varying amounts of surface groups as reinforcement and phenolic resin and coal tar pitch as matrix precursors as discussed by the authors.
TL;DR: In this article, a modified metal spinning process was proposed to produce thin-wall, small-bore tubes in hard-to-work materials such as CP titanium, Incoloy 825, Inconel 600 and Stainless steel AISI-304.
TL;DR: In this article, a thermodynamic study of the As-Ga-In ternary system has been performed using pseudobinary AsGa-AsIn phase diagram and thermodynamic data.
Abstract: A thermodynamic study of the As-Ga-In ternary system has been performed using pseudobinary AsGa-AsIn phase diagram and thermodynamic data, ternary liquidus data, As(Ga 1 − x In x ) pseudobinary layer compositions obtained from liquid phase epitaxy and previously optimised descriptions of the related binary systems, As-Ga, As-In and Ga-In. Isothermal ternary sections and the relevant thermodynamic quantities have been calculated, together with the pseudobinary AsGa-AsIn phase diagram, which was found to exhibit a miscibility gap in the solid phase region.
TL;DR: In this article, the relation of the area average and multidetector dead times to the original electronic dead time is presented. But, it is often not appreciated that these corrections depend on the experiment performed.
Abstract: Dead time corrections in particle counting systems are important for quantitative analysis. It is often not appreciated, however, that these corrections depend on the experiment performed. For surface analysis systems using a stationary beam and a steady counting rate from a spectrometer with single particle detecting electronics, the dead time corrections lead to the simple equations discussed in our earlier work. These concepts translate very directly into SIMS and AES systems with rastered beams and SIMS, XPS and AES systems with multidetectors, to use the same equations, but with area average and multidetector dead times, respectively. The relations of these dead times to the original electronic dead time are presented here.
TL;DR: In this paper, the thermal stability of fluorine-intercalated carbon fibres has been studied using differential thermal analysis and thermogravimetry using polyacrylonitrile-based and pitch-based fibres, either as-received or heat-treated at 3000 °C.
TL;DR: In this paper, the variations of the dielectric constant, the loss tan and the conductivity with the temperature and frequency are analyzed, and the functional relationship between the different values of these values is determined by fitting the observed data with the respective polymeric expressions of the type ϵ ′ = a 0 + a 1 T 2 - lnσ = a + b (T - T 0 ) 2.
Abstract: Results of dielectric measurements conducted on lanthanum heptamolybdate grown by a gel technique employing the system La(NO 3 ) 3 MoO 3 NH 4 OHHNO 3 Na 2 SiO 3 are presented. The variations of the dielectric constant e′, dielectric loss tan δ and conductivity σ with the temperature and frequency are critically analyzed. The dielectric constant increases with temperature at lower frequencies (10 3 Hz), reaching a maximum value of 320 at 125 °C, after which it abruptly decreases. The dielectric loss tan δ and conductivity σ show both a temperature as well as a frequency dependence. The sharp increase in e′ with temperature is attributed to total polarization resulting from a space charge effect. The functional relationship between the dielectric constant, conductivity and temperature is determined by fitting the observed data with the respective polymeric expressions of the type ϵ ′ = a 0 + a 1 T 2 - lnσ = a + b ( T - T 0 ) 2 The non-linearities and anomalous behaviour of the dielectric constant near the transition temperature, supported by hysteresis studies, indicate the possibility of these materials ferroelectric.
TL;DR: In this article, the 4${\mathit{f}}^{14}$6s${S}}-1/2}$ 6s$ {S} 1/2}.
Abstract: The 4${\mathit{f}}^{14}$6s${\mathrm{}}^{2}$${\mathit{S}}_{1/2}$--4${\mathit{f}}^{14}$5d${\mathrm{}}^{2}$${\mathit{D}}_{5/2}$ 411-nm transition in $^{172}\mathrm{Yb}^{+}$ has been measured to be 729 476 868(11) MHz. The frequency was determined by probing a cold cloud of a few $^{172}\mathrm{Yb}^{+}$ ions held in a radio-frequency trap. The frequency measurement is part of a program to locate the 4${\mathit{f}}^{14}$6s${\mathrm{}}^{2}$${\mathit{S}}_{1/2}$--4${\mathit{f}}^{13}$6${\mathit{s}}^{2}$${\mathrm{}}^{2}$${\mathit{F}}_{7/2}$ 467-nm ultranarrow transition in laser-cooled ${\mathrm{Yb}}^{+}$. The 4${\mathit{f}}^{13}$6${\mathit{s}}^{2}$${\mathrm{}}^{2}$${\mathit{F}}_{7/2}$--4${\mathit{f}}^{13}$5d6s${\mathrm{}}^{1}$D[K= 5/2${]}_{\mathit{J}=5/2}$ transition at 638 nm has been driven in order to depopulate the 4${\mathit{f}}^{13}$6${\mathit{s}}^{2}$${\mathrm{}}^{2}$${\mathit{F}}_{7/2}$ state.
TL;DR: In this article, the enthalpies of formation of the intermetallic compounds in the systems have been combined with information available from the literature on the unary data, the phase diagrams of the constituent systems and on the partial Gibbs functions to develop a thermodynamic description of Cd-Hg-Te alloys.
Abstract: Measurements made of the enthalpies of formation of the intermetallic compounds in the systems have been combined with information available from the literature on the unary data, the phase diagrams of the constituent systems and on the partial Gibbs functions to develop a thermodynamic description of Cd-Hg-Te alloys. This work has used the optimisation program developed by Dr H-L. Lukas of the Max Planck Institut fur Metallforschung, Stuttgart, the associated liquid model published by Dr F. Sommer of the same Institute and the MTDATA suite of programs developed at the National Physical Laboratory. The description gives excellent agreement with the available experimental data and the presentation is illustrated with computed binary and ternary phase diagrams, concentrations of the species assumed in the liquid phase and vapour pressures for the solid-liquid equilibria associated with Cd x Hg 1−x Te.
TL;DR: In this paper, the synergic effect of substituent-like ethoxy group on the electronic properties of conducting polyaniline was investigated and it was shown that substituents affect not only the electrochemical polymerization window but also brings about changes in optical and electronic properties.
Abstract: The synergic effect of the substituentlike ethoxy group on the electronic properties of conducting polyaniline was investigated. The presence of substituents affects not only the electrochemical polymerization window but also brings about changes in optical and electronic properties of the parent polymer polyaniline. The study indicates that electrochemical polymerization of (o-ethoxyaniline) yields a conducting polymer that shows a multiple color transition (yellow → green) on switching the potential between the reduced and oxidized states with an electrochromic response time of 40 ms in addition to its solubility in dimethyl sulfoxide, N-methyl pyrrolidinone, etc. However, the chemical polymerization of the monomer yields a crimson red polymer that is less conducting but has solubility in ethanol/methanol. Evaluation of this alcohol soluble polymer as a corrosion inhibitor for iron in acidic medium shows that it offers corrosion inhibition efficiency of 90%. © 1995 John Wiley & Sons, Inc.
TL;DR: In this paper, the minimum pressure of cubic modification was found to be 2.5 GPa at 2100 K. This is the lowest pressure for cBN crystallization employing the catalyst-solvent process and is reported here for the first time.