Showing papers by "National Physical Laboratory published in 2000"

A review of environmental noise and mental health

Abstract: The question of whether environmental noise exposure causes mental ill-health is still largely unanswered. This paper reviews the studies of environmental and industrial noise and mental ill-health published between 1993 and 1998 and suggests possibilities for future research. Recent community based studies suggest high levels of environmental noise are associated with mental health symptoms such as depression and anxiety but not with impaired psychological functioning. Several studies find that self-reported noise sensitivity does not interact with noise exposure to lead to increased vulnerability to mental ill-health. Chronic aircraft noise exposure in children impairs quality of life but does not lead to depression or anxiety. Further research on environmental noise and mental health should be accompanied by more accurate and detailed measurement of noise exposure and consideration of the impact of other environmental stressors and careful measurement of confounding factors such as social class. Target study populations exposed to noise should be chosen to avoid those where noise exposure is likely to have led to noise sensitive individuals moving away from the area. There should also be greater use of standardised instruments to measure a wider range of mental health outcomes. Also other physiological outcomes such as hormonal measures could with benefit be measured simultaneously.

Covalent immobilization of glucose oxidase to poly(O‐amino benzoic acid) for application to glucose biosensor

Abstract: A biosensor for glucose utilizing glucose oxidase (GOX) covalently coupled to poly(o-amino benzoic acid) (PAB; a carboxy-group-functionalized polyaniline) is described. Amperometric response measurements conducted via unmediated and mediated (with ferrocene carboxylic acid and tetrathiafulvalene) reoxidation of GOX show that glucose can be detected over a wide range of concentrations. An enzyme-conducting polymer-mediator model provides for better charge transport in a biosensor. The optimal response, obtained at pH 5.5 and 300 K, lies in the 1–40 mM range. A kinetic plot yields the value of the apparent Michaelis–Menten constant, Kmapp. The operational stability of the PAB-based glucose biosensor was experimentally determined to be about 6 days. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 662–667, 2000

Combined optical and X–ray interferometry for high–precision dimensional metrology

Abstract: The requirement for calibrating transducers having subnanometre displacement sensitivities stimulated the development of an instrument in which the displacement is measured by a combination of optical and X–ray interferometry. The need to combine both types of interferometry arises from the fact that optical interferometry enables displacements corresponding to whole numbers of optical fringes to be measured very precisely, but subdivision of an optical fringe may give rise to errors that are significant at the subnanometre level. The X–ray interferometer is used to subdivide the optical fringes. Traceability to the meter is achieved via traceable calibrations of the lattice parameter of silicon and of the laser frequency. Polarization encoding and phase modulation allow the optical interferometer to be precisely set on a specific position of the interference fringe—the null point setting. The null point settings in the interference fringe field correspond to dark or bright fringes. Null measurement ensures maximum possible noise rejection. However, polarization encoding makes the interferometer nonlinear, but all nonlinearity effects are effectively zero at the fringe set point. The X–ray interferometer provides the means for linear subdivision of optical fringes. Each X–ray fringe corresponds to a displacement that is equal to the lattice parameter of silicon, which is ca .0.19 nm for the (220) lattice planes. For displacements up to 1 m the measurement uncertainties at 95% confidence level are ± 30 pm, and for displacements up to 100 m and 1 mm the uncertainties are ± 35 and ± 170 pm, respectively. Important features of the instrument, which is located at the National Physical Laboratory, are the silicon monolith interferometer that both diffracts X–rays and forms part of the optical interferometer, a totally reflecting parabolic collimator for enhancing the usable X–ray flux and the servo–control for the interferometers.

A new anechoic material for medical ultrasonic applications.

Abstract: This paper describes a newly developed material with acoustic properties that make it ideal for applications as radiation force balance-absorbing targets. The material is now commercially available from National Physical Laboratory (NPL) and is based on a polyurethane rubber. It exhibits an echo reduction of 45 dB, and single-pass transmission loss of 30 dB, both determined at an acoustic frequency of 1 MHz. The composition and structure of the new NPL absorber are presented, along with values for the frequency and temperature variation of the echo reduction and transmission loss. Over the frequency range 1 to 10 MHz, its acoustic properties comply with the requirements for force balance-absorbing targets specified in IEC 61161.

Observation of the 2 S 1 / 2 − 2 F 7 / 2 electric octupole transition in a single 171 Yb + ion

Abstract: The ${}^{2}{S}_{1/2}{(F=0)\ensuremath{-}}^{2}{F}_{7/2}(F=3)$ electric octupole transition in ${}^{171}{\mathrm{Yb}}^{+}$ has been detected by observing quantum jumps in the fluorescence of a single ion held in an electrodynamic trap. The transition frequency has been measured as 642 121 498.1 (0.8) MHz. The extreme weakness of this transition makes it ideally suited as an optical frequency reference of subhertz linewidth. The absolute frequencies of a series of Doppler-free absorptions in tellurium vapor are also reported. One of these absorptions was used as a local frequency reference while locating the electric octupole transition.

Power frequency electromagnetic fields and health. Where's the evidence?

Abstract: Twenty years ago concerns were raised that exposure to power frequency (or extremely low frequency (ELF)) electromagnetic fields (EMFs) may be associated with an increased risk of cancer or other health hazards. Subsequently no associations have been shown between laboratory magnetic field exposures and carcinogenesis in either animal or cellular models. Indeed, studies have demonstrated that magnetic fields are not associated with cancer. However, the puzzle remains that the results of some epidemiological studies may be interpreted as suggesting that living close to high-voltage transmission (HVT) lines appears to increase slightly the risk of childhood leukaemia. Alternatively, these results could result from small biases and errors in individual studies, which might not necessarily be the same in each study. The nature of the epidemiological studies (power-line, wire code, magnetic field or appliance based) appears to determine whether and how the EMFs associated with HVT lines might be a risk factor. It is possible that a simple association with either magnetic or electric field exposure may not be the whole answer, and an alternative mechanism is always a possibility. Although the interpretation of the available evidence by most expert bodies has led them to conclude that exposure to power frequency electric and magnetic fields is not a human health hazard, a working group under the auspices of the US National Institute of Environmental Health Sciences (NIEHS) concluded that there was a possible low risk associated with certain exposures to ELF magnetic fields. NIEHS itself interpreted the finding as insufficient to warrant aggressive regulatory concern but stated that, because virtually everyone is routinely exposed to ELF EMFs, passive regulatory action is warranted, such as a continued emphasis on educating both the public and the regulated community on means aimed at reducing exposures. These analyses, conclusions and advice are not contradicted by subsequent studies, and therefore the conclusion of the World Health Organisation that further research is needed seems valid.

Long term ionospheric electron content variations over Delhi

Abstract: Ionospheric electron content (IEC) observed at Delhi (geographic co-ordinates: 28.63°N, 77.22°E; geomagnetic co-ordinates: 19.08°N, 148.91E; dip Latitude 24.8°N), India, for the period 1975/80 and 1986/89 belonging to an ascending phase of solar activity during first halves of solar cycles 21 and 22 respectively have been used to study the diurnal, seasonal, solar and magnetic activity variations. The diurnal variation of seasonal mean of IEC on quiet days shows a secondary peak comparable to the daytime peak in equinox and winter in high solar activity. IECmax (daytime maximum value of IEC, one per day) shows winter anomaly only during high solar activity at Delhi. Further, IECmax shows positive correlation with F10.7 up to about 200 flux units at equinox and 240 units both in winter and summer; for greater F10.7 values, IECmax is substantially constant in all the seasons. IECmax and magnetic activity (Ap) are found to be positively correlated in summer in high solar activity. Winter IECmax shows positive correlation with Ap in low solar activity and negative correlation in high solar activity in both the solar cycles. In equinox IECmax is independent of Ap in both solar cycles in low solar activity. A study of day-to-day variations in IECmax shows single day and alternate day abnormalities, semi-annual and annual variations controlled by the equatorial electrojet strength, and 27-day periodicity attributable to the solar rotation.

FTIR investigations of solid precursor materials for sol-gel deposition of WO3 based electrochromic films

Abstract: Peroxypolytungstic acid derivative (APTA) and peroxypolytungstic acid derivative coupled with a dicarboxylic acid additive i.e., oxalic acid dihydrate (APTA + OAD) in xerogel form, synthesized by a wet chemistry route were the solid sol-gel precursors for casting WO3 films. These bulk materials have a complex structure owing to the presence of several groups such as acetate, peroxy anions and water molecules in their basic matrix. Additionally, oxalate ions constitute an integral part of the structure in the APTA + OAD xerogel. Detailed FTIR analysis of these coordination compounds has thrown light on the modes of association of the various anions or groups with tungsten metal ion. The mode of coordination of the acetate ion as a bidentate as well as a monodentate ligand enabling chelate formation and the several other chemical linkages prevalent in APTA have been established. Upon the incorporation of OAD in APTA, the net ramifications are drastic changes in the structure inclusive of changes in the nature and strength of metal - ligand bonding, which is exemplified by FTIR studies of (APTA + OAD) xerogel.

Mobile radio propagation path loss studies at VHF/UHF bands in Southern India

Abstract: Field strength measurements at 200, 400 and 450 MHz (VHF/UHF band) were conducted with the field strength meter placed on board a vehicle in Southern India. Observed field strength values were converted into path losses and are compared with different path loss prediction methods like Hata (1980), Egli (1957), Blomquist-Ladell (1974), COST 231 Walfisch-Ikegami (Doble 1996), Walfisch-Bertoni (1988) and ITU-R. These path loss studies are carried out in urban, suburban and open areas in this region. The results showed that Hata's method gave better agreement with observed values in urban, suburban and open regions; the COST 231 Walfisch-Ikegami model is also in good agreement with the observed values in urban and suburban regions, the Egli and Blomquist-Ladell methods showed moderate agreement in open regions only. The agreement of the Walfisch-Bertoni and ITU-R methods with observed values is not good.

Calibration and Monte Carlo modelling of neutron long counters

Abstract: The Monte Carlo technique has become a very powerful tool in radiation transport as full advantage is taken of enhanced cross-section data, more powerful computers and statistical techniques, together with better characterisation of neutron and photon source spectra. At the National Physical Laboratory, calculations using the Monte Carlo radiation transport code MCNP-4B have been combined with accurate measurements to characterise two long counters routinely used to standardise monoenergetic neutron fields. New and more accurate response function curves have been produced for both long counters. A novel approach using Monte Carlo methods has been developed, validated and used to model the response function of the counters and determine more accurately their effective centres, which have always been difficult to establish experimentally. Calculations and measurements agree well, especially for the De Pangher long counter for which details of the design and constructional material are well known. The sensitivity of the Monte Carlo calculations for the efficiency of the De Pangher long counter to perturbations in density and cross-section of the polyethylene used in the construction has been investigated.

Transmission electron microscopy, electron diffraction and hardness studies of high-pressure and high-temperature treated C60

Abstract: TEM and electron diffraction investigations were performed on high-temperature and high-pressure treated polymeric C60 fullerene, prepared at 700, 773 and 800 K in the pressure range of 3-9 GPa, for one hour. A mixed phase of alternating rhombohedral lamellae and tetragonal domains is formed, even at high pressures, with the ratio of polymers being dependent on the pressure applied. At higher temperatures, 900-1173 K, and for a similar pressure range, graphitic `hard' carbon phases formed, via an interpolymer interface instability and/or shear mechanism. This phase exhibited a hardness of 10-15 GPa and a high degree of elastic recovery under indentation. Treatment times of 0.5-30 minutes for the graphitic phase showed the kinetics of graphitization to be slow (~1 h) and proceeding via cross-linked intermediates containing trapped whole C60 cages. The influence of the cross-linking resulted in hardness values up to 33.5 GPa, for a twenty-minute treatment.

Influence of Organic Additive on the Morphological, Electrical and Electrochromic Properties of Sol-Gel Derived WO3 Coatings

Abstract: The WO3 electrode is ubiquitous in an electrochromic device (ECD) and is a common choice as the electrochromic (EC) layer. EC films were deposited on different substrates by spin coating using peroxotungstic acid based precursor solutions followed by appropriate thermal treatment. Many properties of the films, including some of the EC properties dependant on microstructure of the films, were found to be modified by the addition of small amounts of organic acid to the precursor solution. A study of structural, electrical and electrochromic properties of films cast by using precursor solution comprising 0 to 10 wt% of oxalic acid dihydrate (OAD) was carried out in terms of surface morphology, electrical resistance, structure and EC response. The important findings are that the addition of oxalic acid to the precursor solution results in films with excellent EC properties, devoid of cracks and decreases their dc electrical resistance.