Showing papers by "Imperial College London published in 1974"

Lepton Number as the Fourth Color

Abstract: Universal strong, weak, and electromagnetic interactions of leptons and hadrons are generated by gauging a non-Abelian renormalizable anomaly-free subgroup of the fundamental symmetry structure $\mathrm{SU}{(4)}_{L}\ifmmode\times\else\texttimes\fi{}\mathrm{SU}{(4)}_{R}\ifmmode\times\else\texttimes\fi{}\mathrm{SU}({4}^{\ensuremath{'}})$, which unites three quartets of "colored" baryonic quarks and the quartet of known leptons into 16-folds of chiral fermionic multiplets, with lepton number treated as the fourth "color" quantum number. Experimental consequences of this scheme are discussed. These include (1) the emergence and effects of exotic gauge mesons carrying both baryonic as well as leptonic quantum numbers, particularly in semileptonic processes, (2) the manifestation of anomalous strong interactions among leptonic and semileptonic processes at high energies, (3) the independent possibility of baryon-lepton number violation in quark and proton decays, and (4) the occurrence of ($V+A$) weak-current effects.

Frictional constraints on thrust, wrench and normal faults

Abstract: IT is generally true that in ancient fault zones, quartzofeldspathic mylonites which indicate partial plastic yield throughout a volume of rock1, are most extensively developed in association with thrust faults. They are less widespread along wrench faults (unless the finite displacement is very large) and are comparatively rare along normal faults2. The release of seismic energy at shallow depths follows the same general pattern. More than 90% is released in areas of compressive plate interaction, mostly where underthrusting is the dominant mechanism, whereas only 6% is derived from the midocean ridges, where tensional rifting is operative3.

Trace element content and body size in molluscs

Abstract: WHEN trace element concentrations in shellfish are expressed on a weight-specific basis (as µg g−1) highest values are often recorded in the smallest individuals1. In these cases, it is difficult to assess whether observed differences in element tissue concentrations between populations reflect real differences in environmental trace element constitution, or are merely due to variations in body size. This problem can be avoided by determining element concentrations over a range of body sizes and reference made to a specific size for comparative purposes.

Pheromone-regulated anemotaxis in flying moths.

Abstract: Certain male moths flying upwind toward a scent-producing female appear to be guided anemotactically by optomotor reactions to the ground pattern. Loss of the odor stimulus changes the anemotactic angle from into wind to across wind with left-right reversals.

Low Reynolds number flow over a plane symmetric sudden expansion

Abstract: Flow visualization and laser-anemometry measurements are reported in the flow downstream of a plane 3: 1 symmetric expansion in a duct with an aspect ratio of 9·2: 1 downstream of the expansion. The flow was found to be markedly dependent on Reynolds number, and strongly three-dimensional even well away from the channel corners except at the lowest measurable velocities. The measurements at a Reynolds number of 56 indicated that the separation regions behind each step were of equal length. Symmetric velocity profiles existed from the expansion to a fully developed, parabolic profile far downstream, although there were substantial three-dimensional effects in the vicinity of the separation regions. The velocity profiles were in good agreement with those obtained by solving the two-dimensional momentum equation. At a Reynolds number of 114, the two separation regions were of different lengths, leading to asymmetric velocity profiles; three dimensional effects were much more pronounced. At a Reynolds number of 252, a third separation zone was found on one wall, downstream of the smaller of the two separation zones adjacent to the steps. As at the lower Reynolds numbers, the flow was very stable. At higher Reynolds numbers the flow became less stable and periodicity became increasingly important in the main stream; this was accompanied by a highly disturbed fluid motion in the separation zones, as the flow tended towards turbulence.

Trace anomalies in dimensional regularization

Abstract: An unusual perturbation theory anomaly is pointed out. If there exists a trace identity valid in an arbitrary number of dimensions, then employing dimensional regularization can result in an amplitude satisfying the identity in an arbitrary number of dimensions, but the finite part of the amplitude violating it in four dimensions. An example given here is the one-loop neutrino contribution to the graviton propagator. Anomalous behaviour, of a different origin, also occurs in the one-loop photon contribution. Both kinds of anomaly can be removed at the expense of introducingn-dimensional, rather than 4-dimensional, counterterms.

The mechansim of auditory evoked EEG responses.

Abstract: ANALYSIS of the electroencephalogram (EEG) recorded over 0.5–1.0 s immediately following an auditory stimulus, is a well known objective method for evaluating auditory perceptual threshold, for example, in very young subjects. The low-level and visually indistinct individual responses occur in a spontaneous EEG background; hence repeated stimuli are used and the resulting ensemble of post-stimulus EEG signals averaged at each instant of post-stimulus time (PST). An exactly similar method is widely used in studying EEG visual evoked responses and other neuroelectric phenomena1. This averaging procedure is effective in clarifying any consistent response in the presence of spontaneous activity if identical responses are evoked by all stimuli and if the response waveform is uncorrelated with the spontaneous activity; however, neither requirement seems fully to be met in EEG evoked responses generally or in evoked-response audiometry (ERA) specifically. Correlated waveforms imply common Fourier spectral components, and it is recognised that a linear filter method like averaging could only achieve limited success in separating two such waveforms since it requires the waveforms to have different spectral distributions2, in which case, averaging reduces the additive background due to components with frequency outside the spectral band in which the main power of the response waveform occurs. When all consequent improvement has been made in this way, the response waveform may still seem to be degraded by the presence of background activity within the same spectral band, and linear filter methods cannot assist further; the following remarks refer to this situation3.

A burner for mixtures of very low heat content

Abstract: WE must anticipate a growing demand in the future for the means to burn low grade fuels, and fuel/air mixtures which may not even be normally flammable. Upcast gases from coal seams, ventilation air from mines, exhaust gases from a wide variety of industrial processes, and lean methane/air mixtures from some fermenting wastes are examples.

Magnetic impurities in non-magnetic metals

Abstract: The properties of 3d transition metal impurities in simple metal hosts are summarized. There is a short discussion of the basic microscopic models, then the Anderson model is treated in some detail. The next section considers the s-d model and the Kondo effect. The main experimental features are reviewed and finally the question of dilute alloys is considered.

Prediction of laminar flow and heat transfer in helically coiled pipes

Abstract: A calculation procedure for three-dimensional parabolic flows is applied to predict the velocity and temperature fields in helically coiled pipes. The curvature produces a secondary flow and causes departures from the symmetric velocity profile of Poiseuille flow. Predictions are presented of flow and heat transfer in the developing and fully developed regions. Comparisons of the developing and fully developed velocity profiles with experimental data exhibit good agreement. The development of the wall temperature for the case of axially uniform heat flux with an isothermal periphery has been compared with experimental data and the agreement is good. Predictions for fully developed temperature profiles and heat-transfer coefficients also exhibit good agreement with experimental data. Effects of the Dean number on the friction factor and heat transfer are presented.

Primary basalts and magma genesis

Abstract: Three Eocene lavas from Skye, NW Scotland, have been subjected to anhydrous experimental studies within their melting ranges at pressures up to 30 kb Two of these, an olivine-phyric magnesian alkali basalt and a near-aphyric Mg-poor transitional basalt, appear to show four-phase points on their liquidi at high pressures which are thought to have genetic significance From experimental and mineralogical evidence, the magnesian basalt is postulated to be a primary magma, erupted without significant compositional change from its genesis by slight partial melting of a relatively Fe-rich spinel lherzolite upper mantle at about 60 km depth The liquid seems to have had a reaction relationship with Ca-poor pyroxene (pigeonite) in the residual lherzolite Partial crystallization of batches of this magma, delayed during its ascent at depths of about 40 km, is thought to have given rise to the Mg-poor basaltic liquids The third lava studied experimentally, a sparsely olivine-phyric hawaiite, does not have olivine on the liquidus in any part of its anhydrous P-T diagram and therefore cannot have been derived under anhydrous conditions from olivine-saturated sources The mineralogy and chemistry of the lavas are used to support an hypothesis that the hawaiites are products of partial crystallization of pockets of basalt magma at depths approximating to the crust/ mantle boundary beneath Skye, with $$P_{{\text{H}}_{\text{2}} {\text{O}}}$$ rising to sufficient values to make the residual liquids comparatively rich in normative feldspar Finally, the genesis of all other Skye Eocene lavas is reviewed in the light of the new experimental data

On the Mass, Momentum, Energy and Circulation of a Solitary Wave. II

Abstract: By accurate calculation it is found that the speed $F$ of a solitary wave, as well as its mass, momentum and energy, attains a maximum value corresponding to a wave of less than the maximum amplitude. Hence for a given wave speed $F$ there can exist, when $F$ is near its maximum, two quite distinct solitary waves. The calculation is made possible, first, by the proof in an earlier paper ($I$) of some exact relations between the momentum and potential energy, which enable the coefficients in certain series to be checked and extended to a high order; secondly, by the introduction of a new parameter $\omega $ (related to the particle velocity at the wave crest) whose range is exactly known; and thirdly by the discovery that the series for the mass $M$ and potential energy $V$ in powers of $\omega $ can be accurately summed by Pade approximants. From these, the values of $F$ and of the wave height $\epsilon $ are determined accurately through the exact relations $3V=(F^{2}-1)M$ and $2\epsilon =(\omega +F^{2}-1$. The maximum wave height, as determined in this way, is $\epsilon \_{\max}$ = 0.827, in good agreement with the values found by Yamada (1957) and Lenau (1966), using completely different methods. The speed of the limiting wave is $F$ = 1.286. The maximum wave speed, however, is $F\_{\max}$ = 1.294, which corresponds to $\epsilon =0.790$. The relation between $\epsilon $ and $F$ is compared to the laboratory observations made by Daily & Stephan (1952), with reasonable agreement. An important application of our results is to the understanding of how waves break in shallow water. The discovery that the highest solitary wave is not the most energetic helps to explain the qualitative difference between plunging and spilling breakers, and to account for the marked intermittency which is characteristic of spilling breakers.

Temperature effects in the fracture of PMMA

Abstract: Experiments are described in which the fracture toughness,K c, of PMMA has been determined in the temperature range −190 to + 80° C and over the crack speed range of 10−2 to 102 mm sec−1. Single edge notch tension was used for instability measurements but the other data were obtained using the double torsion method. In the range −80 to + 80°C the variations inK c may be described in terms of modulus changes and a constant crack opening displacement criterion. Crack instabilities are correlated with isothermal-adiabatic transitions at the crack tip. Below −80° C there is an inverted rate dependence associated with thermal effects during post-instability crack propagation.

Life-cycle variation of Myzus persicae (Sulz.) (Hom., Aphididae) in different parts of the world, in relation to genotype and environment

Abstract: Life-cycle variation, involving alternative methods of overwintering (holocycly and anholocycly), is found in many important pest aphids, and may have considerable ecological, genetic and economic significance. The occurrence of life-cycle variation in Myzus persicae (Sulz.) in different parts of the world is reviewed. The holocycle of M. persicae, with sexual reproduction and overwintering of eggs on Prunus, occurs in the temperate regions of every continent, and although anholocycly is widespread in warm climates there are indications that the potential for sexual reproduction may be retained throughout the whole range of the species. The environmental factors involved in the determination of sexual morphs are considered. Photoperiodism provides the timing mechanism for sexual morph production, and the photoperiodic response is probably tuned to different regional conditions and buffered against other environmental variables within certain limits. The only other environmental factor clearly implicated in sexual morph production is temperature, and an attempt is made to correlate the global pattern of life-cycle variation in M. persicae with temperature differences between regions, by dividing the world into six zones delimited by selected isotherms. The overall pattern of life-cycle variation can be explained largely on the basis of climatic differences between zones, and the effects of these differences on gene and genotype frequencies within the species. Clones of androcyclic character seem to be widespread and, although genetically isolated anholocyclic biotypes undoubtedly exist, androcyclic clones could be the principal source of parthenogenetic overwinterers in all parts of the world where life-cycle differences exist within populations.

The effect of mean compression or dilatation on the turbulence structure of supersonic boundary layers

Abstract: It is now well known that the turbulence structure of thin shear layers can be strongly affected by the application of extra rates of strain in addition to the shear velocity gradient. Examples of such extra strain rates include lateral divergence or convergence, and streamline curvature in the plane of the mean shear. The changes in Reynolds stress are an order of magnitude larger than would be expected from the explicit extra terms in the Reynolds-stress transport equations, and therefore an order of magnitude larger than predicted by conventional calculation methods. In the present paper, one of a series on ‘complex’ turbulent flows, we show that bulk compression or dilatation (i.e. an extra strain rate div U) also appears to affect turbulent shear layers, typical values of Reynolds stress being increased by compression and decreased by dilatation. The fractional change in Reynolds stress is an order of magnitude larger than the fractional change in volume of a fluid element. The physical mechanism is probably analogous to that responsible for the large effects of divergence or convergence in incompressible flow. Because the phenomenon seems to be of great practical importance we discuss it in the context of engineering calculation methods. An empirical correction formula, analogous to those used to allow for divergence or curvature effects, greatly reduces the large discrepancies found between recent experiments on supersonic boundary layers and calculations by conventional extensions of successful incompressible-flow methods.

Seismicity and Structure of the Zagros (Iran): The Main Recent Fault between 33 and 35 degrees N

Abstract: The most recent tectonic deformation of the Zagros, and in particular the late Quaternary right-lateral wrench movement along the Main Recent Fault, is summarized in the context of the general tectonic history of the range. The seismicity along the Main Recent Fault between latitudes 33 and 35 degrees N is examined, and details are given for several destructive earthquakes, including the 1909 Selakhor earthquake which was associated with over 40 km of surface faulting along a segment of the Main Recent Fault and which is described here for the first time. The relation between the seismicity and the individual fault segments forming the Main Recent Fault is studied and interpreted in terms of a continuing right-lateral strike slip deformation. The implications of this contemporary deformation for the seismotectonics of the Zagros are considered, and in particular its bearing on the problem of the relative motion of the Arabian Plate with respect to Central Iran.

Natural resistance to Salmonella infection, delayed hypersensitivity and Ir genes in different strains of mice.

Abstract: THE development of immunity to an intracellular bacterial infection such as that produced by Salmonella typhimurium in mice can be followed by the fall in the numbers of living bacteria in the liver and spleen. Resistance to infection appears at about the same time as delayed hypersensitivity to appropriate antigens of the infecting organisms and both may be taken as indicators of a cell-mediated immune response1. Inbred mouse strains differ widely in their resistance to salmonella infections and one possible explanation is that they differ in their ability to produce cell-mediated immune responses in general. This has been tested by comparing the degrees of delayed hypersensitivity detectable in different strains of mice sensitised with a number of unrelated antigens. The results discussed here disprove the hypothesis but suggest a more interesting one.

Recovery from cardiac bypass and elective cardiac arrest. The metabolic consequences of various cardioplegic procedures in the isolated rat heart.

Abstract: Isolated perfused working rat hearts were subjected to elective cardiac arrest for 20 or 30 minutes. Various methods of arrest, either singly or in combination and with or without coronary perfusion, were studied. The functional recovery of the heart following the termination of arrest was related to the concentration of adenosine triphosphate (ATP) and creatine phosphate in the myocardium at the end of the period of arrest. In turn, these concentrations depended on the method used to induce arrest. Normothermic ischemic arrest or electrical fibrillation led to a marked reduction in high-energy phosphates and a poor functional recovery. In contrast, coronary perfusion with hypothermic solutions or solutions containing high concentrations of potassium induced arrest without depleting ATP or creatine phosphate. These procedures conferred considerable protection on the myocardium and thus permitted good recovery. The energy status and the recovery associated with ischemic arrest were improved by combining the ischemia with potassium-induced arrest, intermittent coronary perfusion, or hypothermia. In the latter instance, a time- and temperature-dependent relationship was demonstrated. The results stress the importance of maintaining ATP and creatine phosphate levels during arrest; such maintenance requires the provision of a continuous supply of oxygen and nutrient, which may perhaps be best achieved by ensuring continuous and adequate coronary perfusion.