Showing papers by "University College London published in 1982"

Accents of English

Abstract: Accents of English is about the way English is pronounced by different people in different places. Volume 1 provides a synthesizing introduction, which shows how accents vary not only geographically, but also with social class, formality, sex and age; and in volumes 2 and 3 the author examines in greater depth the various accents used by people who speak English as their mother tongue: the accents of the regions of England, Wales, Scotland and Ireland (volume 2), and of the USA, Canada, the West Indies, Australia, New Zealand, South Africa, India, Black Africa and the Far East (volume 3). Each volume can be read independently, and together they form a major scholarly survey, of considerable originality, which not only includes descriptions of hitherto neglected accents, but also examines the implications for phonological theory. Readers will find the answers to many questions: Who makes 'good' rhyme with 'mood'? Which accents have no voiced sibilants? How is a Canadian accent different from an American one, a New Zealand one from an Australian one, a Jamaican one from a Barbadian one? What are the historical reasons for British-American pronunciation differences? What sound changes are currently in progress in New York, in London, in Edinburgh? Dr Wells his written principally for students of linguistics, phonetics and English language, but the motivated general reader will also find the study both fascinating and rewarding.

A new look at the saturn system: the voyager 2 images.

Abstract: Voyager 2 photography has complemented that of Voyager I in revealing many additional characteristics of Saturn and its satellites and rings. Saturn's atmosphere contains persistent oval cloud features reminiscent of features on Jupiter. Smaller irregular features track out a pattern of zonal winds that is symmetric about Saturn's equator and appears to extend to great depth. Winds are predominantly eastward and reach 500 meters per second at the equator. Titan has several haze layers with significantly varying optical properties and a northern polar "collar" that is dark at short wavelengths. Several satellites have been photographed at substantially improved resolution. Enceladus' surface ranges from old, densely cratered terrain to relatively young, uncratered plains crossed by grooves and faults. Tethys has a crater 400 kilometers in diameter whose floor has domed to match Tethys' surface curvature and a deep trench that extends at least 270° around Tethys' circumference. Hyperion is cratered and irregular in shape. Iapetus' bright, trailing hemisphere includes several dark-floored craters, and Phoebe has a very low albedo and rotates in the direction opposite to that of its orbital revolution with a period of 9 hours. Within Saturn's rings, the "birth" of a spoke has been observed, and surprising azimuthal and time variability is found in the ringlet structure of the outer B ring. These observations lead to speculations about Saturn's internal structure and about the collisional and thermal history of the rings and satellites.

On the Stochastic Properties of Bursts of Single Ion Channel Openings and of Clusters of Bursts

Abstract: Characteristics of observed bursts of single channel openings were derived recently for two particular ion channel mechanisms. In this paper these methods are generalized so that the observable characteristics of bursts can be calculated directly for any mechanism that has transition probabilities that are independent of time as long as the process is at equilibrium or is maintained in a steady state by an energy supply. General expressions are given for the distributions of the open time, the number of openings per burst, the total open time per burst, the gaps within and between bursts, and so on. With the aid of these general results a single computer program can be written that will provide numerical values for such distributions for any postulated mechanism, given only the transition rates between the various states. The results are illustrated by a numerical example of a mechanism in which two agonist molecules can bind sequentially, and either singly or doubly occupied receptor ion channels may open. The analogous theory is also given for the case where bursts of channel openings are grouped into clusters; many of the results bear a close analogy with those found for simple bursts.

Infrequent normal B lymphocytes express features of B-chronic lymphocytic leukemia.

Abstract: An infrequent (2-3%) B lymphocyte subpopulation was found in the normal human tonsil and lymph nodes that shows the phenotypic characteristics of B-chronic lymphocytic leukemia (B-CLL) (rosette formation with mouse erythrocytes, weak expression of membrane Ig, staining for HLA-DR, and OKT1 or Leu-1 detecting a T cell-associated p65 antigen). Preliminary evidence suggests that at least a subpopulation of these cells is found, in small proportions, within the germinal centers. These cells were not observed in the human bone marrow. B-CLL may involve this peripheral B lymphocyte subset.

Cholinergic and catecholaminergic receptors in the Xenopus oocyte membrane.

Abstract: 1 Neurotransmitter-receptors in the membrane of Xenopus oocytes have been studied using electrophysiological techniques Neurotransmitters and related agents were applied while recording either membrane potential or membrane current The majority of ovarian oocytes used were at stages IV and V 2 Three types of oocytes were examined: inner ovarian epithelium covered (ec) oocytes; epithelium manually removed (er) oocytes; and collagenase treated (ct) ooctyes 3 Ovarian oocytes are sensitive to some cholinergic and catecholaminergic agents Responses to serotonin were seldom observed and when present were much weaker than responses to other agents No responses were observed to the amino acids: aspartate, glutamate, γ-aminobutyric acid, and glycine; or to octopamine and histamine 4 Acetylcholine (ACh) usually depolarized the membrane, in a dose-dependent manner, with threshold concentrations as low as 10-9 m The ACh-potential was due to an increase in Cl permeability and had a reversal potential around — 19 mV The intracellular Cl ion activity, measured with a Cl-ion sensitive micro-electrode, was about 65 mm and the estimated Cl-ion equilibrium potential, ECl, agreed with the reversal potential of the ACh-potential 5 Curare (10-4 m), tetrodotoxin (10-6 m), or α-bungarotoxin (10-6 g/ml) did not block the response to 10-6 m-ACh; whereas atropine (10-7 m) blocked it No response to nicotinic agents (eg nicotine, 1,1-dimethyl-4-phenylpiperazinium) was observed These results suggest that the ACh receptors in the oocyte membrane are muscarinic in nature 6 The apparent latency of the ACh potential, examined by ionophoretic application of ACh to er oocytes and ct oocytes, ranged from 0·5 sec to over 20 sec Intracellular injection of ACh was without effect 7 Responses to catecholamines were observed mostly in ec oocytes; while in er and ct oocytes they were rare and of very small amplitudes 8 The usual response to both dopamine and (—)-epinephrine was a transient hyperpolarization manifested by an initial increase in K-permeability followed by a decrease The latency of these responses ranged from 10 sec to over 30 sec and their reversal potential was nearly — 100 mV, which coincided with EK 9 Oocytes responded to the β-adrenergic receptor agonist, isoproterenol, as well as (—)-epinephrine Pre-treatment with the β-adrenergic receptor blocker, propranolol, abolished the response to both (—)-epinephrine and (—)-isoproterenol The dopamine potential was also reduced considerably Both the α-adrenergic receptor agonist, phenylephrine, and the α-adrenergic receptor blocker, phentolamine, were without effect 10 Maturation of the oocytes, induced in vivo by gonadotropin or in vitro by progesterone, led to loss of responsiveness to both cholinergic and catecholaminergic agents

A calcium-dependent transient outward current in Xenopus laevis oocytes

Abstract: Membrane currents were investigated in Xenopus laevis oocytes under voltage clamp. Depolarizing pulses, given from a holding potential of about –100 mV, elicited a transient outward current when the membrane potential was made more positive than about –20 mV. As the potential was made increasingly positive the transient outward current first increased and then decreased. The amplitude of the transient current increased when the external Ca 2+ concentration was raised; and the current was abolished by Mn 2+ . It appears that when the membrane is depolarized Ca 2+ ions enter the oocyte and trigger an outward current, possibly by opening Cl – channels.

Muscle protein synthesis measured by stable isotope techniques in man: the effects of feeding and fasting.

Abstract: 1. Measurements have been made of whole-body and skeletal muscle protein synthesis in fed and fasted adults with L-[1-13C]leucine. 2. The marked increase in whole-body synthesis on feeding largely reflects the changes in protein synthesis in muscle, which doubles on feeding, compared with a 40% increase in that of the rest of the body. 3. Skeletal muscle in fed man contributes more than half to total protein synthesis occurring in the whole body.

The effects of substance P on histamine and 5-hydroxytryptamine release in the rat

Abstract: 1. Substance P (SP) induces histamine release from isolated rat peritoneal mast cells at concentrations of 0.1-10 muM.2. Inhibitors of glycolysis and oxidative phosphorylation prevent the release of histamine induced by SP.3. Cells heated to 47 degrees C for 20 min release histamine when treated with an agent causing cell lysis but fail to release in response to SP.4. SP does not release histamine by interacting with cell-bound IgE.5. Histamine release by SP is rapid, with more than 90% of the response occurring within 1 min of the addition of the peptide to mast cells at 37 degrees C.6. Substance P, unlike antigen-antibody or compound 48/80, does not show enhanced release of histamine when calcium (0.1-1 mM) is present in the extracellular medium but calcium increases the response to SP when the ion is added after the peptide. Extracellular calcium (0.1-1 mM), magnesium (1-10 mM) and cobalt (0.01-0.1 mM) all inhibit SP-induced histamine release when added before the peptide. Pre-treatment of the cells with EDTA (10 mM) and washing in calcium-free medium inhibits the histamine release induced by SP.7. Histamine release induced by SP was optimum at an extracellular pH of 7.2.8. A number of peptides structurally related to SP were examined for histamine-releasing activity. At the concentrations tested, the N-terminal dipeptides Lys-Pro and Arg-Pro, tuftsin, physalaemin, eledoisin, SP(3-11), SP(4-11) and [p-Glu(6), p-amino Phe(7)]-SP(6-11) were all found to be inactive. The relative activities of the other peptides were: [Formula: see text]9. Rat basophilic leukaemia cells (RBL-2H3) fail to respond to SP at concentrations which activate rat mast cells. Release of 5-hydroxytryptamine by immunological activation of RBL cells is not changed by the presence of SP.10. The mechanism of action of SP on mast cells and the nature of the SP receptor on mast cells is discussed in relation to SP receptors in other cell types.

DNA strand breaks and ADP-ribosyl transferase activation during cell differentiation.

Abstract: The nuclear enzyme ADP-ribosyl transferase (ADPRT) catalyses the formation of poly(ADP-ribose)-modified chromatin proteins from NAD+ (refs 1–5) and is entirely dependent on DNA6 containing nicks7–11. Nuclear ADPRT activity is required for efficient DNA excision repair12,13, probably because it regulates DNA ligase activity14. Indirect evidence has suggested that ADPRT activity may also be involved in control of gene expression and cell differentiation15–21. We report here an obligatory involvement of ADPRT activity in the differentiation of muscle cells. Inhibitors of ADPRT activity reversibly inhibit both fusion of myoblasts to form multi-nucleate muscle fibres and the differentiation-specific increase in creatine phos-phokinase (CPK) activity. These two markers of differentiation can also be reversibly inhibited by depriving the cells of nicotinamide and thus lowering their cellular NAD content. Specific gene expression sometimes requires gene rearrangements or DNA transposition; this implies that DNA strand-breaking and rejoining might be involved in gene expression. We also describe the appearance during cytodifferentiation of single-strand DNA breaks which are not due to a general deficiency in DNA repair.

Long-term synaptic enhancement and short-term potentiation in rat fascia dentata act through different mechanisms

Abstract: 1. The component processes contributing to post-activation change in synaptic efficacy in the perforant pathway to the fascia dentata were studied in rats under sodium pentobarbitone anaesthesia. 2. With low stimulus strength, which activated only a relatively small number of perforant path fibres, repetitive stimulation led to effects which had very similar characteristics to those observed at neuromuscular synapses under similar conditions. Paired shocks resulted in a short (∼ 100 ms) facilitation superimposed on a depression, possibly due to depletion of available transmitter, which recovered more slowly (∼ 4 s). Short trains of stimuli at 125-250 Hz led to a longer lasting increase in synaptic strength which decayed to control levels with a double exponential time course. The two exponential components behaved like augmentation and potentiation at neuromuscular synapses, with time constants at 33 °C of about 5 s and about 90 s respectively. 3. High-intensity stimulus trains of identical frequency and duration led to an enhancement of synaptic strength which lasted for longer than 30 min. 4. The paired shock depletion effect was increased in direct proportion to the amount of augmentation and potentiation present following low-intensity stimulus trains. Following high-intensity trains the paired shock depletion effect was increased by the same amount, and recovered with the same time course as following low-intensity stimulus trains, even though there remained a significant enhancement of the synaptic response. 5. The results are interpreted as indicating that augmentation and potentiation are due to an increase in the probability of transmitter release whereas long-term enhancement acts through some other, as yet undetermined, mechanism. Following high-intensity stimulation all three processes are activated.

The interaction between waves and a turbulent current: waves propagating with the current

Abstract: This paper describes an experimental programme carried out in a laboratory channel with rough and smooth beds, to investigate the interaction between gravity waves and a turbulent current. In particular, changes induced in the mean-velocity profiles, turbulent fluctuations, bed shear stresses and wave attenuation rates are considered for a range of wave heights, keeping the wave period constant. The smooth-boundary tests were carried out as a necessary preliminary to the more-realistic rough-boundary condition. A directionally sensitive laser anemometer was used to measure horizontal, vertical, and 45° velocity components in the oscillating fluid, and an on-line minicomputer was programmed to produce ensemble averages of velocities, Reynolds stresses and wave-elevation data. The cycle was sampled at 200 separate phase positions, with 180 observations at each position. Measurements were made at up to 30 points in the vertical. Preliminary tests were carried out on the unidirectional current and on the waves alone. These show that mean-velocity profiles and turbulence parameters of the current agree satisfactorily with previous experiments, and that the waves are approximated closely by Stokes’ second-order theory. For combined wave and current tests, mean-velocity profiles are generally found to differ from those suggested by a linear superposition of wave and current velocities, a change in boundary-layer thickness being indicated. However, shear stresses at the smooth boundary are found to be described by such a linear addition.

Calcium‐ and length‐dependent force production in rat ventricular muscle

Abstract: 1. Trabeculae from the right ventricles of rat hearts were ;skinned' by immersion for 30 min in a solution containing the non-ionic detergent Brij-58 at a concentration of 1%.2. The average sarcomere length in the central region of the relaxed preparation was estimated by laser diffraction and set at pre-determined values within the range of 1.9-2.4 mum by adjustment of muscle length. Isometric contractions were then induced by raising the Ca(2+) concentration under carefully controlled chemical conditions.3. The dependence of Ca(2+)-activated force production on sarcomere length over the ascending limb of the length-force relation was examined at Ca(2+) concentrations giving partial and full activation of the contractile system of the muscle.4. The dependence of Ca(2+)-activated force on Ca(2+) concentration was compared at sarcomere lengths on the ascending limb and plateau of the length-force relation.5. The results obtained from both kinds of experiment showed that the sensitivity of the contractile system to Ca(2+) increases with sarcomere length over the ascending limb of the length-force relation.6. Possible explanations for this observation have been discussed.

Chromosomal localization of human cellular homologues of two viral oncogenes.

Abstract: Acute transforming RNA tumour viruses represent genetic recombinants between type C retro viral sequences and transformation-specific sequences of cellular origin. Of the known mammalian cell-derived transforming genes (oncogenes), two have been shown to encode proteins with either intrinsic or highly associated tyrosine-specific protein kinase activity. One such gene, c-fes, is of cat cellular origin, while the second, c-abl, was derived from mouse cellular sequences. We now show that the human equivalents of c-fes and c-abl are localized on human chromosomes 15 and 9, respectively. These findings exclude the possibility that these transformation-related genes are clustered at a single locus within the human genome. It is of interest that both of these chromosomes are involved in specific rearrangements found in certain forms of human cancer.

Defect energetics in α - Al 2 O 3 and rutile Ti O 2

Abstract: We report a theoretical survey of defect energetics in $\ensuremath{\alpha}$-${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$ and rutile Ti${\mathrm{O}}_{2}$ which we relate to structural and transport properties of these materials. The study of these crystals has required us to modify our computational methods based on the Mott-Littleton theory, which were previously confined to the treatment of cubic materials. We discuss the theoretical aspects of a new and quite general computational procedure, HADES III, which can be used for defect calculations on crystals of any symmetry. Our discussion pays particular attention to the effects on the calculated energetics of the use of Mott-Littleton methods adapted for anisotropic crystals. Other features, considered in detail, are the sensitivity of calculated defect energies to the choice of lattice potential and to the size of the atomistically simulated region surrounding the defect. We also compare our results for $\ensuremath{\alpha}$-${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$ and those of an earlier study of Dienes et al. Our calculations are then used to discuss the simplest features of the defect properties of pure and doped $\ensuremath{\alpha}$-${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$ and Ti${\mathrm{O}}_{2}$. The present results support the dominance of Schottky disorder in both crystals; cation Frenkel energies are high and anion Frenkel pairs may be of significance in $\ensuremath{\alpha}$-${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$. In addition we present a survey of doped alumina and of the effect of oxygen partial pressure on the defect structure of this material. Our results suggest that defect clustering will have a major influence on the properties of doped ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$.

Impulsive phase of flares in soft X-ray emission

Abstract: Observations using the Bent Crystal Spectrometer instrument on the Solar Maximum Mission show that turbulence and blue-shifted motions are characteristic of the soft X-ray plasma during the impulsive phase of flares, and are coincident with the hard X-ray bursts observed by the Hard X-ray Burst Spectrometer. A method for analysing the Ca xix and Fe xxv spectra characteristic of the impulsive phase is presented. Non-thermal widths and blue-shifted components in the spectral lines of Ca xix and Fe xxv indicate the presence of turbulent velocities exceeding 100 km s-1 and upward motions of 300–400 km s-1.

Ionic regulation of egg activation.

Abstract: Developing cells have constantly to make decisions: when to proliferate and divide, when and how to differentiate. It is an increasingly attractive idea that these decisions involve changes in intracellular cation concentrations. Our ideas about the mechanisms of changes in intracellular cations come largely from the application of biophysical techniques in the study of excitable tissues. These ideas are proving very valuable to the investigation of the control of proliferation and cell development and it is evident that the ionic mechanisms which pertain in nerve and muscle have their counterparts in other cells. Just as alterations in intracellular ion concentrations serve a signalling function in excitable tissue, so too they act as signals during development. Since almost all the quantitative data on the ionic mechanisms of fertilization come from work on sea urchins we have confined our review to sea urchin eggs.

Glare from windows: current views of the problem

Abstract: This paper discusses daylight glare as a source of visual discomfort in terms of glare from the unobstructed sky and not glare related to direct or reflected sunlight. There is a difference between...

Cytoplasmic structure in rapid-frozen axons.

Abstract: Turtle optic nerves were rapid-frozen from the living state, fractured, etched, and rotary shadowed. Stereo views of fractured axons show that axoplasm consists of three types of longitudinally oriented domains. One type consists of neurofilament bundles in which individual filaments are interconnected by a cross-bridging network. Contiguous to neurofilament domains are domains containing microtubules suspended in a loose, granular matrix. A third domain is confined to a zone, 80-100 nm wide, next to the axonal membrane and consists of a dense filamentous network connecting the longitudinal elements of the axonal cytoskeleton to particles on the inner surface of the axolemma. Three classes of membrane-limited organelles are distinguished: axoplasmic reticulum, mitochondria, and discrete vesicular organelles. The vesicular organelles must include lysosomes, multivesicular bodies, and vesicles which are retrogradely transported in axons, though some vesicular organelles may be components of the axoplasmic reticulum. Organelles in each class have a characteristic relationship to the axonal cytoskeleton. The axoplasmic reticulum enters all three domains of axoplasm, but mitochondria and vesicular organelles are excluded from the neurofilament bundles, a distribution confirmed in thin sections of cryoembedded axons. Vesicular organelles differ from mitochondria in at least three ways with respect to their relationships to adjacent axoplasm: (a) one, or sometimes both, of their ends are associated with a gap in the surrounding granular axoplasm; (b) an appendage is typically associated with one of their ends; and (c) they are not attached or closely apposed to microtubules. Mitochondria, on the other hand, are only rarely associated with gaps in the axoplasm, do not have an appendage, and are virtually always attached to one or more microtubules by an irregular array of side-arms. We propose that the longitudinally oriented microtubule domains are channels within which organelles are transported. We also propose that the granular material in these channels may constitute the myriad enzymes and other nonfibrous components that slowly move down the axon.

The spreading of a drop by capillary action

Abstract: A small drop placed on a horizontal surface will spread under the action of capillary forces until it reaches an equilibrium position. The rate at which it spreads provides a means for testing certain hypotheses about moving contact lines; namely that there must be slip between the fluid and the solid boundary near the rim of the drop to avoid a force singularity there, and that the contact angle measured at the rim itself does not show the dynamic behaviour observed by measurements that ignore rapid changes in slope in the immediate vicinity of the rim but remains equal to its static value.By the use of matched asymptotic expansions, an equation for the rate of spread of a drop as a function of the radius of the contact circle is obtained. Experiments on the spreading of small drops of molten glass allow a comparison to be made between the spreading of a drop determined experimentally and that predicted theoretically, which supports the use of the proposed hypotheses as appropriate for the study of fluid motions containing moving contact lines.

Translation of Exogenous Messenger RNA Coding for Nicotinic Acetylcholine Receptors Produces Functional Receptors in Xenopus Oocytes

Abstract: Messenger RNA extracted from the electric organ of Torpedo was injected into Xenopus oocytes. This led to the synthesis and incorporation of functional acetylcholine receptors into the membrane of the oocyte. When activated by acetylcholine these Torpedo acetylcholine receptors in the oocyte membrane opened channels whose ionic permeability resembled that of nicotinic receptors in other cells.