Showing papers by "University College London published in 1976"
TL;DR: In this article, a series of relevance weighting functions is derived and is justified by theoretical considerations, in particular, it is shown that specific weighted search methods are implied by a general probabilistic theory of retrieval.
Abstract: This paper examines statistical techniques for exploiting relevance information to weight search terms. These techniques are presented as a natural extension of weighting methods using information about the distribution of index terms in documents in general. A series of relevance weighting functions is derived and is justified by theoretical considerations. In particular, it is shown that specific weighted search methods are implied by a general probabilistic theory of retrieval. Different applications of relevance weighting are illustrated by experimental results for test collections.
1,889 citations
TL;DR: The results suggest that place units were not responding to a simple sensory stimulus nor to a specific motor behavior, and are interpreted as strong support for the cognitive map theory of hippocampal function.
1,730 citations
TL;DR: The concept that each nerve cell makes and releases only one nerve transmitter (widely known as Dale's Principle) has been re-examined and experiments suggesting that some nerve cells store and release more than one transmitter have been reviewed.
609 citations
TL;DR: Direct immunofluorescence is used to demonstrate cells with intracellular IgM and no detectable surface Ig in mouse foetal liver as early as 12 d gestation, suggesting that B lymphocyte precursors synthesise IgM several days before they incorporate these molecules into their plasma membranes as cell-surface receptors for antigen.
Abstract: IN BALB/c mice, surface immunoglobulin (Ig)-bearing B lymphocytes are first detectable by immunofluorescence at 17 d gestation in the liver and spleen1. Explants of 14-d foetal liver1 and spleen2, and 15-d bone marrow (our unpublished observations), have been shown to generate Ig-bearing B cells in vitro after 4–7 d of culture, suggesting that B lymphocytes normally develop multifocally in the haemopoietic tissues of mice. We have used direct immunofluorescence to demonstrate cells with intracellular IgM and no detectable surface Ig in mouse foetal liver as early as 12 d gestation. Our results suggest that B lymphocyte precursors synthesise IgM several days before they incorporate these molecules into their plasma membranes as cell-surface receptors for antigen.
393 citations
Book•
30 Jan 1976TL;DR: In this paper, the authors present a bibliography index of names of the Greeks and their neighbours in the Hellenistic world, including Polybius and Posidonius, from Antiochus III to Pompey.
Abstract: Preface 1. The Greeks and their neighbours in the Hellenistic world 2. Polybius and Posidonius 3. The Celts and the Greeks 4. The Hellenistic discovery of Judaism 5. Greeks, Jews and Romans from Antiochus III to Pompey 6. Iranians and Greeks Select bibliography Index of names.
319 citations
Book•
01 Jan 1976TL;DR: The authors surveys 100 years of military inefficiency from the Crimean War, through the Boer conflict, to the disasterous campaigns of the First World War and the calamities of the Second.
Abstract: This unique and penetrating book surveys 100 years of military inefficiency from the Crimean War, through the Boer conflict, to the disasterous campaigns of the First World War and the calamities of the Second. It examines the social psychology of military organizations, provides case studies of individual commanders and identifies an alarming pattern in the causes of military disaster.
277 citations
TL;DR: This article reported the results of a preliminary attempt to establish the age of a series of late Quaternary lake sediments in the Rub' al Khali desert of the Arabian Peninsula.
Abstract: A GOOD deal of information on late Quaternary moist periods in East Africa and Australia, derived largely from the dating and analysis of lake sediments, has been collected over recent years1–4. Although fossil lake beds have long been known to exist in Arabia5–7, they have received scant attention. I report here the results of a preliminary attempt to establish the age of a series of late Quaternary lake sediments in the Rub' al Khali desert of the Arabian Peninsula. More detailed palaeoclimatic implications will be considered elsewhere later.
272 citations
TL;DR: In this article, a simple type of corrugated surface is examined, and the effective slip coefficient calculated, for grooves of finite and infinite depth, when the grooves are filled with one fluid and another fluid flows over them.
Abstract: When an interface between two fluids moves in contact with a solid boundary, the Navier-Stokes equations and the no-slip boundary condition provide an unsatisfactory theoretical model, because they predict an undefined velocity at the contact line and a non-integrable stress on the solid boundary. If the surface irregularities are included in the model, the flow on a length scale large compared with their size can be calculated, using a slip coefficient and treating the surface as smooth.A simple type of corrugated surface is examined, and the effective slip coefficient calculated, for grooves of finite and infinite depth. The slip coefficient when the grooves are filled with one fluid and another fluid flows over them is also calculated. It is suggested that, when a fluid displaces another on a rough surface, the displaced fluid remains in the hollows on the surface, thus providing a partly fluid boundary for the displacing fluid and leading to a slip coefficient for the flow.Fluid contained between two vertical plates and rising between them provides a simple example of a flow for which the solution can be found with and without a slip coefficient. With slip present, the force on the plates is finite and its value is calculated.
264 citations
TL;DR: In this paper, the formation of the electron-density trough region which lies equatorward of the auroral oval was studied with a special emphasis on the formation formation of electron density trough region.
Abstract: The dynamics of the nighttime high-latitude F region is studied with special emphasis on the formation of the electron-density trough region which lies equatorward of the auroral oval. It is found that the absence of photoionization together with ordinary ionic recombination and slow plasma convection velocity can give a deep trough over a period of many hours. However, the normal global pattern of electric fields has regions of plasma convection sufficiently rapid to affect the rate of O(+) + N2 reactions and to speed the rate of ionospheric decay. In addition, the escape of thermal plasma via the polar winds as well as N2 vibrational excitation and enhanced N2 densities act to deplete the ionosphere. In combination, these destructive processes can readily account for the great variety of troughs found by experimentation. Thus, it appears that there is no single cause for the observed troughs, but that at various times, different processes act together to create density depressions of substantial magnitude.
263 citations
TL;DR: Against classical expectations were the following findings: localisation of touch and pressure stimuli was reasonably accurate on both sides, and repeated sub threshold stimulation markedly lowered the threshold for detecting von Frey hairs.
Abstract: The spinal cord of a patient had been completely and cleanly cut across at the Th3 segment except for part of one anterolateral quadrant. The extent of the lesion was clearly verified at an open surgical inspection. There was complete paralysis below the level of the lesion. The classical expectations of her sensory status were confirmed in only 2 ways: (1) Temperature could be identified only on the side opposite the intact quadrant. (2) Pin prick could be only identified on this contralateral side. Against classical expectations were the following findings: (1) Localisation of touch and pressure stimuli was reasonably accurate on both sides. (2) Passive movement could be detected on the homolateral side. (3) Pain could be evoked by stimulation of both sides. (4) Von Frey hair stimuli could be identified on both sides. (5) Repeated sub threshold stimulation markedly lowered the threshold for detecting von Frey hairs. This case implies that there must be a revision of the traditional labelling of the function of the spinal cord afferent systems.
232 citations
TL;DR: It was concluded that following partial de Afferentation, the remaining afferents can establish connection with deafferented cells but the data presented did not allow a conclusion as to whether the new connections were produced by sprouting or by the unmasking of existing connections.
TL;DR: The present experiments with Phaeodactylum tricornutum Bohlin have tested the concept of light intensity adaptation and suggested that growth at a suboptimal light intensity did enhance the ability to utilize lower light levels.
Abstract: The historical background on adaptation of algae to various light intensities is analysed It is argued that there is little evidence to suggest that previous growth at low light intensities enhances the ability of an alga to utilize these low light levels Rather, the published evidence suggests that the most general response to growth at sub-optimal light intensities is a reduced ability to utilize saturating levels The present experiments with Phaeodactylum tricornutum Bohlin have tested this concept of light intensity adaptation Changing photosynthetic abilities during batch growth depended on the light intensity used for growth and these changes affected interpretations of the data When measurements were made intensities appeared to photosynthesize (at all intensities) better than did those grown at higher light levels When the changes during batch growth were taken into account, or when the alga was grown in turbidostat cultures, a different picture was obtained Growth at reduced light intensities was accompanied by (a) increased chlorophyll content, (b) decreased rate of light-saturated photosynthesis expressed on a chlorophyll, cell number or cell protein basis, and (c) decreased activity of RuDP carboxylase One result suggested that growth at a suboptimal light intensity did enhance the ability to utilize lower light levels The light-saturation curve of cells grown in batch culture at 07 klux showed higher slopes at the low light intensities than did those grown at 12 klux This was most marked when photosynthesis was expressed per cell, but was also apparent when it was put on a per chlorophyll basis
TL;DR: The results suggest that deafferentation results in the unmasking of normally ineffective connections, which could be a mechanism which explains many of the observed changes in the responses of central nervous system neurons following lesions.
TL;DR: Three new peptides have been isolated from the venom of the common European honey bee: one is a fragment of the known peptide melittin, and some properties of the peptides are described.
Abstract: A procedure is described for the simultaneous separation of all the peptides (other than those present in trace amounts) contained in the venom of the common European honey bee (Apis mellifera). Three new peptides have been isolated: one is a fragment of the known peptide melittin. Some properties of the peptides are described.
TL;DR: The experiments reported here demonstrate that the perception of experimentally induced pain in normal human subjects is not altered by administration of the opiate antagonist naloxone.
Abstract: RECENT studies have revealed the existence of endogenous morphine-like compounds in the central nervous system1–3 and in the pituitary4. These compounds, named enkephalin1 and C-fragment4, have been reported to produce analgesia when injected intraventricularly in rats and cats5,6 and to be antagonised by naloxone which is a potent antagonist of narcotic analgesics. They also have a high affinity for the opiate receptor, which has been discovered in the central nervous system of vertebrates including man7, and they can displace naloxone from these receptors2–4. There is substantial evidence that central grey structures in the midbrain are intimately involved in analgesia. Electrical stimulation8 and microinjection of morphine9,10 in these regions produce analgesia which is antagonised by naloxone. Stimulation of the central grey region in humans11 has been reported to produce marked analgesia which is antagonised by small doses of naloxone12. In addition, acupuncture analgesia has been reported to be antagonised by naloxone13. These findings have led to the hypothesis that there may be an ongoing release within the brain of a morphine-like compound which is partially responsible for pain thresholds. If this were so, then the antagonism of the effects of the endogenous compound by naloxone should affect pain perception. The experiments reported here demonstrate that the perception of experimentally induced pain in normal human subjects is not altered by administration of the opiate antagonist naloxone.
TL;DR: From the flavin content and dodecylsulphate-polyacrylamide electrophoresis it is inferred that the native enzyme is a dimer composed of similar subunits of 50000 molecular weight.
Abstract: Glutathione reductase from human erythrocytes exists predominantly as an entity of 100000 molecular weight under various conditions of pH and ionic strength. The s20,w of 5.5 S and D20,w of 50 μm2/s correlate with the molecular weight determined by sedimentation equilibrium. The homogeneity of this species is primarily dependent on the presence of thiols and secondarily on high concentrations of salt.
The amino-acid composition of the enzyme shows similarities both with glutathione reductases from other sources and with lipoamide dehydrogenase.
From the flavin content and dodecylsulphate-polyacrylamide electrophoresis it is inferred that the native enzyme is a dimer composed of similar subunits of 50000 molecular weight.
In the absence of thiols, glutathione reductase shows a tendency to form tetramers and larger aggregates.
Although these larger species are also catalytically active, under cellular conditions the presence of its product, reduced glutathione, should maintain the enzyme as the dimeric entity.
TL;DR: In many areas of the brain, GABA is also taken up by glial cells and in some areas, this glial uptake may actually predominate, and the transport processes for GABA in neurones and glia have remarkably similar properties but do appear to have slightly different structural requirements.
Abstract: IT is now generally accepted that GABA is an important inhibitory synaptic transmitter in the vertebrate central nervous system. However, there remain many problems in elucidating the precise roles of GABA in the brain. One important problem is the existence of a glial pool of GABA which makes it difficult to determine the origin of GABA released during experiments designed to demonstrate the release of GABA after nervous stimulation. It was thought at one time that this problem might be overcome by utilising the uptake processes for GABA to label the neuronal GABA pools, with for example, 3H-GABA. However, it is now clear that in many areas of the brain, GABA is also taken up by glial cells and in some areas, this glial uptake may actually predominate. The transport processes for GABA in neurones and glia have remarkably similar properties but do appear to have slightly different structural requirements.
TL;DR: This paper aims to deduce the fundamental phenomena of information science, starting from two premises: that information science is a problem-oriented discipline concerned with the effective transfer of desired information from human generator to human user and that the single notion common to all concepts of information now extant is that of change of structure.
Abstract: This paper aims to deduce the fundamental phenomena of information science, starting from two premises: that information science is a problem-oriented discipline concerned with the effective transfer of desired information from human generator to human user, and that the single notion common to all concepts of information now extant is that of change of structure.
From these premises, a spectrum of information concepts is derived, and a partition of that spectrum particular to the purposes of information science is described. From this partition, the terms text and information (both in information science) are defined, and the fundamental phenomena of information science are deduced: the text and its structure, the structure of the recipient and changes in that structure, and the structure of the sender and the structuring of the text.
These phenomena are seen as the basic components of the mechanisms of the channel, which have been the traditional area of interest to information science. Some implications of this approach for research in information science are discussed in this paper.
And, finally, the question of the ethics of theoretical research in information science is raised, and a restrictive condition is proposed.
TL;DR: An alternative approach is described here, in which the freeze-fracture technique has been used to study tight junctions of the sheep choroid plexus during foetal development, and the results obtained suggest that there is no change in the ultra-structural features of Tight junctions which have previously been suggested to correlate with transepithelial permeability, in spite of considerable changes in permeability.
Abstract: ELECTRON microscopical investigations of tight junctions (zonulae occludentes) using marker substances, have indicated that in some tissues these junctions may represent an extracellular pathway for transepithelial movement of certain small solutes1 and also restrict the movement of larger solutes2. The electrical resistance across some epithelial tissues has been used as a measure of the degree of permeability of the tight junctions to ions3, and it was suggested that junctions that are “leaky” to ions are also leaky to small non-electrolytes. Examination of tight junctions with the freeze-fracture technique has revealed the presence of a network of intramembranous fibrils4 or strands5,6. Some evidence suggests that these strands constitute the sealing component of the junction7, and Claude and Goodenough6 correlated the transepithelial permeability of a given epithelium with the number of strands in the tight junction network. Artificial methods of altering transepithelial permeability (hypertonic solutions applied to the mucosal side of the epithelium) have been used to investigate changes in transepithelial electrical resistance8, and freeze-fracture morphology9 or both10. Results from these studies do not consistently support the above correlation. An alternative approach is described here, in which the freeze-fracture technique has been used to study tight junctions of the sheep choroid plexus during foetal development. The results obtained suggest that there is no change in the ultra-structural features of tight junctions which have previously been suggested to correlate with transepithelial permeability, in spite of considerable changes in permeability during the developmental period studied11–13.
TL;DR: In all cases the leukaemic blast cells showed greatly diminished expression of cholera toxin receptors when compared to granulocytic cells from the chronic phase of CML, which parallels weak or negligible expression of the cholERA toxin receptor in ALL and AML.
Abstract: SUMMARY. Fourteen cases of Philadelphia chromosome (Ph1) positive chronic myeloid leukaemia in blast transformation have been investigated using cell surface markers. Morphologically eight cases were lymphoid and the remainder myeloid in appearance. All cases were negative with surface markers for thymocytes and T and B lymphocytes. Five of the lymphoid cases reacted with an antiserum specific for acute lymphoid leukaemia (ALL) of non-T non-B type and were also weakly reactive with a lymphocyte reactive antiserum. A sixth patient, whose blast cells were anti-ALL negative (ALL-) at presentation, subsequently developed central nervous system leukaemia with anti-ALL positive (ALL+) blast cells in the CSF. In all cases the leukaemic blast cells showed greatly diminished expression of cholera toxin receptors when compared to granulocytic cells from the chronic phase of CML. This parallels weak or negligible expression of the cholera toxin receptor in ALL and AML.
These results suggest that the blastic phase of CML may involve different cellular derivatives of a pluripotential stem cell in which the primary malignant/genetic changes reside. The blast crisis of CML can therefore be heterogeneous with respect to cellular expression and in a significant proportion of patients involves a cell which is by membrane markers and morphological criteria indistinguishable from that seen in the common form of ALL. In these cases the Philadelphia chromosome may be the only distinguishing cellular characteristic.
TL;DR: Results imply that “latent” connections of some sort exist between afferents and cells in the gracile nucleus, and that these latent connections are unmasked by partial deafferentation, which is initially poor, but increases greatly with time.
TL;DR: Homing to the intestines seemed a general property of T cells activated to transplantation antigens, which was observed irrespective of whether the T.TDL were activated against H2 determinants, M-locus determinants or H2-plus M- locus determinant.
TL;DR: On the basis of membrane marker analysis with an antiserum made against acute lymphoblastic leukaemia and other immunological markers it is suggested that some chronic myeloid leukaemias (C.M.L.L.'antigen-positive and have terminal transferase enzyme activity might benefit from therapy usually given in typical Philadelphia-chromosome-negative A.L.) patients in blast crisis.
TL;DR: The phase changes in the hydrous minerals have been studied by means of differential thermal analysis, X-ray diffraction and optical microscopy, and will be more fully described elsewhere as discussed by the authors.
01 Jan 1976
TL;DR: Sewall Wright has provided the best general classification of the processes changing gene frequency under the simplified conditions outlined in Chapter 1, and it is used in the following account.
Abstract: Micro-evolution consists of change in the population either to fit it to a new place or time in a changing environment, or to improve its success in a constant environment. The modifications which take place are genetic. Sewall Wright pointed out in an article written in 1949 that ‘the elementary evolutionary process in a reasonably large homogeneous population maybe considered to be change in gene frequency’. He has provided the best general classification of the processes changing gene frequency under the simplified conditions outlined in Chapter 1, and it is used in the following account.
TL;DR: Using cultures of a number of different marine algae, it is suggested that photosynthesis in marine diatoms depends on an active PEPCase utilizing bicarbonate as a substrate and that a less active RuDPCase utilizes CO2.
Abstract: SUMMARY
Using cultures of a number of different marine algae (diatoms Skeletonema costatum (Grev.) Cleve and Phaeodactylum tricornutum Bohlin, chrysophyte Isochrysis galbana Parke, green flagellate Dunaliella tertiolecta Butcher, dinoflagellate Gonyaulax tamarensis Lebour) the short-term, pattern of 14CO2 assimilation has been investigated. In all except D. tertiolecta the labelling of amino acids and intermediates of the tricarboxylic acid (Krebs) cycle was significantly heavier than that of sugar phosphates. Over periods of 30–120 s labelling in amino acids and Krebs cycle intermediates accounted for 41–95% of the 14C fixed (depending on the alga). Over shorter times (< 10 s) the pattern in the 2 diatoms showed significant labelling of C4 acids (and related com-pounds) and little labelling of sugar phosphates. The reverse wits seen with D. tertiolecta. Also, in the 2 diatoms and in G. tamarensis significant inhibition of photosynthesis by oxygen could only be achieved with 100% oxygen; atmospheric levels having little effect. Parallel measurements of 2 carboxylating enzymes showed that ribulose-1,5-diphosphate carboxylase (RuDPCase) was significantly greater than phospho (enol)pyruvate carboxylase (PEPCase) activity only in the green flagellate. It is suggested that photosynthesis in marine diatoms depends on an active PEPCase utilizing bicarbonate as a substrate and that a less active RuDPCase utilizes CO2. In D. tertiolecta the pattern more closely resembles that of a “Calvin (C3)” plant. The dinoflagellate and the chrysophyte appeared to show a mixed C3 and C4 photosynthesis.
TL;DR: Human fibroblasts containing a translocation between the X chromosome and chromosome 15 were fused with the 6-thioguanine-resistant mouse cell line, IR, and hybrids, selected in HAT medium, retained the X/15 chromosome.
Abstract: Human fibroblasts containing a translocation between the X chromosome and chromosome 15 were fused with the 6-thioguanine-resistant mouse cell line, IR. Resulting hybrids, selected in HAT medium, retained the X/15 chromosome. Hybrids which were counterselected in 6-thioguanine lost this chromosome. The X-linked markers glucose-6-phosphate dehydrogenase (G6PD), phosphoglycerate kinase (PGK), and hypoxanthine phosphoribosyl transferase (HPRT), and the non-X-linked markers pyruvate kinase (PKM2) mannose phosphate isomerase (MPI), N-acetyl hexosaminidase A (HEXA) and β2-microglubulin (β2-m) all segregated in concordance with the X/15 translocation chromosome. The latter markers have been assigned to chromosome 15. Selection against the X/15 chromosome was done using antihuman β2-m serum. Electrophoretic and immunochemical analyses of the N-acetyl hexosaminidases A and B in these hybrids were performed.