Abstract: Analysis of an almost complete mammalian mitochondrial DNA sequence has identified 23 possible tRNA genes and we speculate here that these are sufficient to translate all the codons of the mitochondrial genetic code. This number is much smaller than the minimum of 31 required by the wobble hypothesis. For each of the eight genetic code boxes with four codons for one amino acid we find a single specific tRNA gene with T in the first (wobble) position of the anticodon. We suggest that these tRNAs with U in the wobble position can recognize all four codons in these genetic code boxes either by a "two out of three" base interaction or by U.N wobble.

Abstract: The nucleotide sequence spanning the ribosomal RNA (rRNA) genes of cloned human mitochondrial DNA reveals an extremely compact genome organization wherein the putative tRNA genes are probably ‘butt-jointed’ around the two rRNA genes. The sequences of the rRNA genes are significantly homologous in some regions to eukaryotic and prokaryotic sequences, but distinctive ; the tRNA genes also have unusual nucleotide sequences. It seems that human mitochondria did not originate from recognizable relatives of present day organisms.

Abstract: Studies of dredged and drilled samples from the North Atlantic ocean have revealed that basalts with a wide range of major and trace element compositions have been generated at the Mid-Atlantic Ridge (M.A.R.). Many of the basalts erupted between latitudes 30° and 70° N do not have the geochemical characteristics of normal mid-ocean ridge basalts (m.o.r.b.) depleted in the more-hygromagmatophile (hyg.) elements. Drilling along mantle flow lines transverse to the ridge has shown that different segments of the M.A.R. have produced basalts with a distinct compositional range for tens of millions of years. As more data have become available, the nature and scale of this variation have been established and tighter constraints can now be placed on the petrogenetic processes involved. The rare earth elements are used to test quantitatively the effects of open and closed system fractional crystallization, equilibrium partial melting (including continuous melting), zone refining and mantle mixing processes on basalt chemistry. When evaluated in terms of the more-hyg. elements, the results show that major heterogeneities must exist in the mantle sources feeding the M.A.R. Ratios of many of the more-hyg. elements remain consistent in space and time in basalts erupted at a particular ridge segment, but vary widely between different ridge segments. These ratios are not significantly modified by the processes of basalt generation. The hyg. element relations provide a major constraint on the nature of heterogeneity in the Earth’s mantle and the processes producing it. The mantle sources of anomalous ridge segments can be best explained in terms of variable veining of a hyg. element depleted host by a hyg. element enriched liquid or fluid generated by very small degrees of partial melting. Such incipient melting, as well as subduction zone processes, may be viable mechanisms for changing hyg. element ratios in the mantle source regions on the scale observed. These processes can be integrated into a model for mantle evolution which involves (1) upward migration of incipient melts to provide a hyg. element enriched source for alkali basalts and a hyg. element depleted source for normal m.o.r.b., and (2) extraction of continental crust and recycling of the depleted residue into the mantle at subduction zones. Also, some recycling of continental material into the mantle may be required to explain Pb isotope patterns.

Abstract: The volatile content of glassy pillow rims from East Scotia Sea back-arc basin (BAB) lavas are unlike those of mid-ocean ridge (MOR) pillow-rim glasses, although non-volatile compositions of the two rock groups overlap. The East Scotia Sea samples have three to ten times greater water contents and nearly twice the average CO 2 and Cl contents of MOR samples; F contents are similar. S contents are only one-third those from MOR samples. H 2 O and CO 2 contents of glassy pillow rims from Mariana island arc andesites are similar to those in the BAB lavas studied. Nevertheless, volatiles in the East Scotia Sea BAB magmas are probably not directly derived from the subducted slab, because there is no seismic evidence that the slab extends within 200 km of the spreading axis of the East Scotia Sea. Available data do not preclude the possibility that the magmas were contaminated by seawater prior to eruption or that the mantle under the East Scotia Sea spreading center is volatile-rich. The volatiles may have been added to the mantle during an earlier period of subduction, perhaps during the initial formation of the East Scotia Sea basin.

Abstract: The equilibrium conditions on distended reconnected field lines in the distant geomagnetic tail are investigated on the assumption that the field line tension is balanced by tail lobe ‘mantle’ plasma convecting into the central current sheet Subject to steady reconnection at a neutral line being possible at some point in the tail we show that steady solutions can be obtained for arbitrary down-tail variations of mantle influx Results are presented for a simple but physically plausible model in which the mantle density and bluk speed at the current sheet increase steadily down-tail Acceleration of lobe plasma in the current sheet is also discussed, and the consequent structure of the hot plasma regions down stream from the neutral line

Abstract: Whistler components received by the VLF goniometer at Halley, Antarctica, have been scaled for nose frequency and direction of arrival. The data were taken from two separate one hour periods on either side of local midnight (0023–0133 UT and 0340–0450 UT, 5 June 1975). Because of the high whistler occurrence rate at this time and the rapid processing facilitated by the Sheffield semi-automated whistler analyser, it has been possible to scale 1850 whistler components and hence obtain high resolution mapping of the whistler duct structure. The number of observable ducts increased from 4 at 0030 UT to about 15 at 0130 UT and had reached about 31 by 0400 UT. This increasing number of ducts together with an observed clustering of ducts in the second one hour period, provides evidence for duct formation. The observations have been compared with the various duct generation mechanisms which have been proposed. The duct formation process may have been associated with a negative change in Dst which occurred at the same time, and this possibility is discussed.

Abstract: We report on the detection of the ferromagnetic resonance of Ni and Fe films through the photoacoustic effect. The photoacoustic signal dependence on both the magnetic field and the chopping frequency is also discussed in light of existing theoretical models for the production of the photoacoustic signals.

Abstract: ESR experiments on dilute Ag: Dy thin films at liquid-helium temperatures allow the estimation of lower limits for the second-order orbit-lattice coupling parameters. The anisotropy observed on the $g$ value of the ${\ensuremath{\Gamma}}_{7}$ ground state of Dy is interpreted in terms of admixtures of excited crystal-field levels with the ground state, via a planar strain of the film, induced by the difference in the thermal-expansion coefficients between the film and the substrate. The results indicate that the tetragonal orbit-lattice parameter agrees in sign with that predicted by the point-charge model, but the trigonal one does not, similar to Ag: Er thin films.

Abstract: Development of chick embryos was studied following injection of thyroxine or the goitrogen thiourea and compared with that in control saline-injected eggs. The three stages recorded (onset of beak clapping, clicking, and hatching movements) all occurred late in embryos treated with thiourea on the 16th day of incubation. Thyroxine-treated eggs hatched significantly early only when incubated in groups in contact. This suggests that an acceleration effect of thyroxine reported in previous work may have represented an unreliable effect of thyroxine coupled with the synchronizing effect of contact with other eggs. Changes in hatching times following hormone injection are compared with these associated with effects of clicks, which are known to regulate developmental rate and to play a part in the synchronization of hatching.

Abstract: Distribution functions are calculated for photoexcited electrons in GaAs, under conditions of continuous, monochromatic excitation. The lattice temperature is taken to be 1.2 K and the excitation intensity such that the density of photoexcited carriers is insufficient for the distribution to be affected by intercarrier scattering. A Boltzmann equation approach is used to take account of the effects of, injection of electrons into the conduction band, at an energy below the threshold for longitudinal optical phonon emission, scattering by acoustic phonons, via the deformation potential and piezoelectric interactions, and recombination. The equation is solved numerically using an iterative technique and the distribution functions are found to differ significantly from a Maxwellian form. Emission spectra due to conduction band to neutral acceptor transitions are derived from the computed distribution functions and are compared with recent experimental results.

Abstract: 1. 1. The effect of oxygen tension, p o 2 , on oxygen uptake and tolerance to anoxia have been studied by exposure in nitrogen atmosphere and diving in the water snakes Helicops modestus and Liophis miliaris , at 25°C. 2. 2. The critical P o 2 , was the same (70mmHg O 2 ) for both species, but below that tension H. modestus showed a higher degree of dependence on P o 2 . 3. 3. Anoxia tolerance time was longer (14 min for H. modestus and 4 min for L. miliaris ) during forced dive than during exposure to a 100% nitrogen atmosphere. No difference was found in pre- and post-forced dive oxygen uptake values in both species. 4. 4. The maximum duration of a voluntary dive was shorter than the mean tolerance time to forced dives in L. miliaris . but longer in H. modestus . 5. 5. H. modestus , the more aquatic species, is significantly more tolerant of complete anoxia (100% N 2 exposure) and submersion.

Abstract: A unique transfer RNA has been identified in human and bovine mitochondria that lacks the "dihydrouridine" loop and stem structure. This tRNA is mitochondrially coded as shown by DNA sequence analysis of the human and bovine mitochondrial DNA. Sequence analysis of the RNA shows that it is post-transcriptionally modified by the addition of CCA at the 3' terminus and that at least one base is modified. As predicted by its anticodon (GCU, corresponding to the serine codons AGU/C) this tRNA can be aminoacylated with serine when purified mitochondria are incubated in a medium containing 3H-serine.