Showing papers in "Philosophical transactions - Royal Society. Mathematical, physical and engineering sciences in 1969"

Sound Generation by Turbulence and Surfaces in Arbitrary Motion

Abstract: Monograph on sound generation by turbulence and surfaces in arbitrary motion, discussing sound and multipole fields and governing equations

Interpretation of radio echo sounding in polar ice sheets

Abstract: Experimental results are presented from a traverse over the ice sheet of north western Greenland in 1964, during which a continuously recorded profile of ice thickness was obtained for the first time. Interpretation of data from this traverse is consistent with results of subsequent work to December 1967. The parameters of the apparatus are presented briefly, while the details of electronic circuits are being published separately. Theoretical problems of radio wave propagation in an ice sheet and, in particular, the factors affecting accuracy are discussed. The uncertainty in depth, over a small area, is ±5 m ±1.5% and this is verified by comparison with the seismic results for a range of depths up to 1.5 km. It is found that the only real uncertainty arises in irregular terrain. The effectiveness of the radio echo technique is dependent on the absorption of radio waves in ice. Temperature, and to a lesser extent the impurity content of ice, appear to be the main variables affecting field performance. Earlier laboratory results on the variation of absorption with temperature for ice cores from northwest Greenland, together with theoretically predicted temperature distributions throughout the ice mass, have provided estimates of the total loss by absorption. These estimates are reasonably consistent with the observed echo strengths over most of the traverse. Consequently, it is predicted that echoes can be obtained over considerable areas of the ice sheets of Greenland and Antarctica, as has been verified by subsequent observations. The reflexion coefficient at the ice/rock interface is of the order of —15 dB. It could rise to 0 dB for an ice/water interface and one area was found in Greenland where it appeared to fall to — 30 dB. Results from this traverse have shown that local surface slopes on the ice sheet are largely controlled by variations of longitudinal stress along the line of flow. Regional slopes over several kilometres vary with the velocity of movement of the ice, but appear to be less dependent on basal ice temperatures than laboratory results would suggest. The velocity of ice movement increases in proportion to the square or cube of the basal shear stress, but the stress itself shows no obvious dependence on basal ice temperature. Partially reflecting layers discovered within the ice mass are discussed mainly in terms of small density variations between adjacent layers of ice. One particularly prominent layer is calculated to be about 1000 years old and its variation of depth with position provides evidence in favour of the steady state model of the ice sheet.

Marine Geology of the Atlantic Continental Margin of Europe

Abstract: A geological reconnaissance has been made of the continental slope of western Europe between the Faeroe Isles and Lisbon by means of a 60 kj reflexion profiler, supplemented by Boomer profiles and extensive Asdic (side-looking sonar) coverage of the continental shelf. A tentative interpretation of these profiles has been made by references to available rock samples and seismic refraction data. The first-formed continental slope deposits of the north-east Atlantic appear to be Cretaceous in age. Massive erosion (particularly of the continental shelf) preceded the Tertiary phase of downwarping which allowed upbuilding and outbuilding of the continental margin and was followed by a latest-Tertiary and Quaternary phase of important faulting, canyon erosion, slumping and deposition. This episodic evolution of the European continental margin is thought to indicate two phases of continental drift. In contrast to the ground west of the British Isles and France the steep and narrow northern and western continental margins of Iberia show only a little upbuilding and only local outbuilding. The work was done from aboard R.R.S. Discovery II or R.R.S. Discovery (with the exception of a Sparker profile obtained by H.M.T.S. Alert ), the powerful profiler being used in 1965, the Asdic on many cruises between 1958 and 1967.

Excitation of Forbidden Lines in Gaseous Nebulae I. Formulation and Calculations for 2p$^{q}$ Ions

Abstract: A formulation is given for electron collisions with ions in configurations 1s$^{2}$2s$^{2}$2p$^{q}$ and 1s$^{2}$2s$^{2}$2p$^{6}$3s$^{2}$3p$^{q}$. The main approximation is neglect of coupling to other configurations. Hartree-Fock functions are used for the ion states and the complete wave functions are expressed as sums of vector-coupled anti-symmetrized products of ion functions and orbitals for the colliding electron. Variational principles are used to obtain coupled integro-differential equations for the radial functions for the colliding electron, and to correct results obtained from approximate solutions of these equations. All algebraic reductions are carried out without the introduction of subsidiary approximations, and conservation and reciprocity theorems are therefore satisfied exactly. Expressions are tabulated for all algebraic coefficients. Numerical calculations are made in two approximations: in the exact resonance approximation, used only for p-waves, the wave functions are calculated with quadrupole interactions neglected; and in the distorted wave approximation the wave functions are calculated from static central potentials. Variational corrections are calculated and are found to be reasonably small. It is concluded that the final corrected results should agree closely with results which would be obtained from exact solutions of the coupled equations. Collision strengths are calculated for all inelastic collisions in configurations 1s$^{2}$2s$^{2}$2p$^{q}$, q = 1 to 5, for at least three different energies, and for values of the residual charge z = 1, 2, 3, 4, 5 and the limit of z $\rightarrow \infty $. Results may be interpolated for all members of the iso-electronic sequences. Results for energies such that some channels are open and others closed are obtained by means of extrapolation techniques.

Millimetre and Submillimetre Astronomy

Abstract: Measurements of lunar radiation at a wavelength of 1.2 mm are described and discussed. It is found that the lunar poleward darkening function T(Xf)/T(0X) varies considerably more rapidly with latitude V than is predicted by a plane homogeneous model. Preliminary calculations using a centimetre scale roughness model are described. The results account well for the measured values of the darkening function at 1.2 mm as well as for measurements of the corresponding function at both longer and shorter wavelengths. Close to lunar dawn upland lunar areas appear to have higher brightness temperatures than the maria. Some measurements of the partial solar eclipse of 20 May 1966 are reported together wit observations of radiation from the planet Jupiter. The relative advantages of Fourier transform and filter spectroscopy at millimetre and submillimetre wavelengths are discussed. A possible experiment to detect the cosmic thermal 3 °K background at 1.3 and 1.9 mm length is discussed.

Infrared day and night airglow of the Earth's upper atmosphere

Abstract: A list is presented of the principal emission features of the airglow spectrum in the infrared and the expected intensities and altitude distributions are discussed. The day and night airglow emission of the atmosphere in the infrared region of the spectrum may be a serious hindrance to infrared astronomy but it can provide valuable information on thie energy content of the atmosphere and of the reactions that take place. Most of the infrared emission of the Earth's atmosphere arises from minor constituents, of which the most important are 1120 and CO2 and their isotopes. Also produced at the surface of the Earth are the infrared active constituents CH4, N20, CO and NO2. At high altitudes, the action of solar radiation gives rise to 03, H202, HO2, OH, NO, CO and NO+.

Semiclassical dispersion theory of lasers

Abstract: This present paper is an attempt to describe the operation of a laser by a method patterned closely after the classical theory of dispersion. There, the electromagnetic field is treated as a classical system interacting with a collection of classical harmonic oscillators which are at rest. In the present case the radiation field is still treated classically, but, in accordance with the correspondence principle, the oscillators are now virtual oscillators associated with the up-and-down transitions in effective two-state atoms which are described quantum mechanically. The atoms carrying these virtual oscillators are not at rest but move with different velocities. We show how the Lorentz averaging can be performed for such systems, and derive a closed set of equations linking the average electric field E, with the average polarization density P„ and the average population inversion density Mp associated with atoms moving with the velocity v. Next, we investigate the conditions for the existence of a steady state if pumping is present, and if the electric field is represented by a standing wave, or a travelling wave of a single frequency (single-mode case). It turns out that, notwithstanding the nonlinear nature of the equations, the steady-state conditions give a simple complex dispersion relation; moreover, the real and imaginary part of this dispersion relation are equivalent to the usual heuristic expressions which specify the operating frequency in terms of the index of refraction and cavity length, and which balance the gain against the losses. The single-mode case is analysed in detail without any smallness assumptions for the resultant intensity. The small-intensity case gives the usual results exhibiting the tuning dip. For high intensities the relative depth of the dip tends to zero. At the end of the paper we discuss proposed extensions and additional applications.

Near infrared night sky background.

Abstract: Night sky background observation by near IR radiation flux, using rocket-borne telescope and ground based equipment

Expected infrared spectra of gaseous nebulae.

Abstract: If we are asked why we want to use the infrared to observe gaseous nebulae, we might reply with George Mallory, who was asked why he wanted to climb Mount Everest, ‘Because its there’. More specifically, one reason is the very great space penetration possible in the infrared. Diffuse nebulae characteristically are close to the galactic plane, and interstellar extinction therefore prevents the observation of distant objects. At MATHS FORMULA the mean range to which diffuse nebulae can easily be observed is about 1500 parsecs (pc), while many of these nebulae are so reddened as to be nearly unobservable at Hβ. It is for this reason that at present the observation of diffuse nebulae is almost entirely limited to our own spiral arm and its immediate neighbours. However, because of the decrease of interstellar extinction to longer wavelengths, at 1 μm the range of observation would be about 3000 pc; at 2 μm about 10 000 pc, comparable with the distance to the centre of the Galaxy; and at 10μm, about 100 000 pc, far larger than the diameter of the Galaxy. (The form of the interstellar reddening curve is from Whitford 1958.)

High Resolution Spectra of the Sun

Abstract: The University of Liege has operated, since 1958, a laboratory of solar spectroscopy at the International Scientific Station of the Jungfraujoch (Switzerland). During recent years, much effort has been devoted in two main directions: ( a ) techniques of correction for the effects of the instrumental function to obtain the best possible knowledge of central intensities and profiles of photospheric lines; ( b )increase of the signal to noise ratio in the records in order to detect and measure very faint absorption features. In addition, a balloon-borne equipment is now under construction in Liege to observe, with maximum resolution, the near infrared solar spectrum from an altitude of about 80 000 ft.

Project to Map the Sky in the Infrared from an E.S.R.O. Satellite

Abstract: One of the experiments installed in the TD1 E.S.R.O. satellite (expected launching date 1970), will be devoted to a mapping of the sky in the lead sulphide region. The scanning will be obtained by the motion of the satellite itself, so a relatively simple infrared photometer will be used.

Extragalactic Radio Sources in the Infrared

Abstract: My purpose is to describe the properties of extragalactic radio sources and to emphasize those measurements in the infrared which will contribute to our understanding of these objects. Since most of the radio sources have only been studied down to wavelengths of a few centimetres, and if an optical identification has been made they may also have been studied in the range 0.4 to 1.0 μm, observations at any infrared wavelengths between 1μm and say 2 mm will be of value. However, only a limited number of radio sources are likely to be detectable with present-day techniques over an appreciable part of this wavelength range. We will endeavour to suggest the types of sources which most merit study and are intense enough to be detected.