Search Results - (Author, Cooperation:R. M. Williams)

2018-09-19

National Academy of Sciences

0027-8424

1091-6490

Biology

Medicine

Natural Sciences in General

Artificial Molecular Machines Special Feature

2013-06-01

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

2015-07-15

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Animals ; *Cycloaddition Reaction ; Porifera/*metabolism ; Pyrroles/*chemical synthesis

2015-10-10

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Climate ; Exhumation ; *Lakes ; *Mars ; Paleontology

2018-04-19

American Association for the Advancement of Science (AAAS)

2375-2548

Natural Sciences in General

2018-01-12

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Geosciences

Computer Science

Medicine

Natural Sciences in General

Physics

Genetics, Microbiology

1471-0528

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

A prospective study of 300 consecutive deliveries has been made to assess the benefits and acceptability of ambulation during spontaneous labour. Ambulation during the first stage occurred in 48 patients with 55 non-ambulant patients acting as controls. No difference in the length of first or second stage, incidence of fetal distress or mode of delivery was observed. In spite of the lack of apparent advantage to the fetal condition, ambulation was acceptable to both patients and nursing staff and should not be discouraged.

Electronic Resource

1365-2559

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Ultrastructural appearances of a small intestinal inflammatory fibroid polyp are reported. There is a vascular scaffolding, with interstices which contain regular and fibrous long-spacing type collagen, condensed lamellar basement membrane fibroblasts, basophils, some eosinophils and histiocytes. In addition other cells less easily characterized but believed to be of an endothelial and primitive mesenchymal cell nature are recognized. Possible origins of the polyp are considered.

Electronic Resource

1365-2559

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

An ovarian and rectal carcinoid within the same person is described. The ovarian carcinoid is non-argentaffinic with typical regular granules. The rectal tumour consists of two types of APUD cells, some argentaffinic and diazo-positive, whilst others are non-argyrophilic. These features are mirrored ultrastructurally, some cells containing the large pleomorphic argentaffinic granules while others have smaller regular granules. In addition, focal aggregates of microfilaments were found in both tumour types. These findings are discussed in terms of the APUD concept. The similarities of the APUD tumour cells to D1 APUD cells of the duodenum is highlighted, and an alternative explanation for their derivation is proposed.

Electronic Resource

1365-2230

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

We report the case of premenstrually exacerbated benign familial pemphigus which showed dramatic improvement with subcutaneous goserelin, a gonadotrophin-releasing hormone analogue. Total abdominal hysterectomy and bilateral salpingo-oophorectomy and oestrogen replacement therapy sustained the improvement.

Electronic Resource

1572-8358

Springer Online Journal Archives 1860-2000

Biology

Summary A simple model, illustrating the transition from a population of free swimming, solitary cells (Chlamydomonas-type) to one consisting of small colonies (Gonium-type) serves as a basis to discuss the evolution of the cooperative group. The transition is the result of a mutation of the dynamics of cell division, delayed cell separation leads to colonies of four cells. With this mutation cooperative features appear, such as synchronised cell divisions within colonies and coordinated flagellar function which enables the colony to swim in definite directions. The selective advantages under given, environmental conditions are defined and the periods necessary for complete allelic replacement in small populations are calculated for asexual and sexual reproduction. The assumption of a steady-state population during allelic substitution is critically considered, particularly under conditions of competition. It is shown that density-dependent population control must operate in the process of selection. Sexual reproduction slows down the rate of selection even though all cells dre haploid. This phenomenon can be explained in general terms of `organizational dominance', where individual units coordinate the function of their neighbours which may be of a different allelotype. Cooperativity is pointed out as an a priori systemic feature which resides in the sub-units of systems, group formation and coordination appears thus as an almost inevitable event. A particular type of system described as ‘closed cycle of positive fitness interaction’ is discussed in more detail. It has the remarkable feature that its members cannot compete with each other; selection takes place between whole cycles (in analogy to Eigen's 1971 model). Gonium has a wide spectrum of `somatic plasticity' which enables it to assume various colonial configurations depending on physiological and environmental conditions. This feature can be explained as the result of dynamic flexibilities on the macro-molecular level. The particular relationship between the vast, molecular complexity and the relative simple dynamics of the cell cycle must lead eventually to the genetic fixation of an environmentally induced phenotype.

Electronic Resource

1572-8358

Springer Online Journal Archives 1860-2000

Biology

Summary The dynamics of populations of self-replicating, hierarchically structured individuals, exposedto accidents which destroy their sub-units, is analyzed mathematically, specifically with regardto the roles of redundancy and sexual repair. The following points emerge from this analysis:0 1. A population of individuals with redundant sub-structure has no intrinsic steady-statepoint; it tends to either zero or infinity depending on a critical accident rate α c . 2. Increased redundancy renders populations less accident prone initially, but populationdecline is steeper if a is greater than a fixed value α d . 3. Periodic, sexual repair at system-specific intervals prevents continuous decline and stabilizesthe population insofar as it will now oscillate between two fixed population levels. 4. The stabilizing sexual interval increases with increased complexity provided this is accom-panied by appropriate levels of redundancy. 5. The model closely simulates the dynamics of heterosis effects. 6. Repair fitness is a population fitness: the chance of an individual being repaired is a functionof the statistical make-up of the population as a whole at that particular period. Populationsliving at α 〉 α c either engage in sexual repair at the appropriate time or they die out. 7. The mathematical properties of the model illustrate mechanisms which possibly played arole in the evolution of a mortal soma in relation to sexual reproduction.

Electronic Resource

1572-8838

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Electrical Engineering, Measurement and Control Technology

Abstract In order to circumvent the corrosion problems prevalent in many existing electrochemical couples using the Na/β″-alumina half cell, a new class of high energy density organic materials was studied as cathode materials. In particular, one material tetracyanoethylene (TCNE), has favourable electrochemical characteristics with a potential 〉3.0 V against Na+/Na and energy density ∼620 Wh kg−1. Adopting a cell designed to permit sealing the anode half cell, the performance of TCNE was evaluated under various experimental conditions, that is, at different concentrations of TCNE in the catholyte and with different current collectors. The electrochemical behaviour of the TCNE cathode and the kinetics of TCNE reduction were examined. The kinetic parameters, exchange current density and diffusion coefficient, were determined from different a.c. and d.c. electrochemical techniques and evaluated with respect to the changes in TCNE concentrations in the catholyte. A chemical transformation occurring in the cell operating conditions which does not reduce the electrochemical activity of TCNE was identified from FTIR spectra. Finally, possible approaches to the use of TCNE or other organic materials in sodium or lithium rechargeable batteries are outlined.

Electronic Resource

1572-8838

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Electrical Engineering, Measurement and Control Technology

Abstract Columnar, porous, magnetron-sputtered molybdenum and tungsten films show optinum performance as AMTEC electrodes at thicknesses less than 1.0 μm when used with molybdenum or nickel current collector grids. Power densities of 0.40 W cm−2 for 0.5 μm molybdenum films at 1200 K and 0.35 W cm−2 for 0.5 μm tungsten films at 1180 K were obtained at electrode maturity after 40–90 h. Sheet resistances of magnetron sputter deposited films on sodium beta″-alumina solid electrolyte (BASE) substrates were found to increase very steeply as thickness is decreased below about 0.3–0.4 μm. The a.c. impedance data for these electrodes have been interpreted in terms of contributions from the bulk BASE and the porous electrode/BASE interface. Voltage profiles of operating electrodes show that the total electrode area, of electrodes with thickness 〈2.0 μm, is not utilized efficiently unless a fairly fine (∼1×1mm) current collector grid is employed.

Electronic Resource

1434-6052

Springer Online Journal Archives 1860-2000

Physics

Abstract We discuss the quantization of Regge's discrete description of Einstein's theory of gravitation. We show how the continuum theory emerges in the weak field long wavelength limit. We also discuss reparametrizations and conformal transformations.

Electronic Resource

1420-9071

Springer Online Journal Archives 1860-2000

Biology

Medicine

Summary Leucocyte cultures were used in four species of Falconiformes for the purpose of karyotypic sex determination and the establishment of a breeding pair. The Andean condor has 80 Guiana eagle 54, Crane hawk 66, and Turkey vulture 76 chromosomes with readily distinguished ZW elements in the female.

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] SIR - In the recent paper by Atwood et al.1 on a purification procedure for C6o and C70 by selective complexation with calixarenes, it was implied that we had previously studied the complexation of C60 with cyclodextrins2. In fact, we used calix[8]arenes as the selective host spe-cies; but ours ...

Electronic Resource

1420-9098

Springer Online Journal Archives 1860-2000

Biology

Résumé Des renseignements sont présentés sur les périodes et les heures de vol deCubitermes ugandensis etC. testaceus en Ouganda oriental. Presque tout le travail s'est effectué au laboratoire. Les ailés retirés du monticule étaient grégaires et négativement phototactiques. L'emploi des ailes renversa ces caractères. Les ailés nevolaient que s'ils étaient hors de contact avec d'autres termites de la colonie et dans la lumière. Des observations ont été faites sur l'intensité de la lumière et l'activité de vol chezC. ugandensis. La pariade ou un essai de pariade stimula l'amputation des ailes chez les deux espèces, mais, du moins chezC. ugandensis, cette stimulation n'était pas obligatoire. Après l'amputation des ailes, les adultes se montraient indifférents à la lumière. Par l'enlèvement artificiel des ailes, on a démontré que le rapport entre la perte des ailes et la perte de la phototaxie positive chezC. ugandensis n'est pas direct. Il y a une discussion des moyens utilisé par les, adultes pour perdre leurs ailes. En général, chez les deux espèces, les femelles n'adoptaient la posture d'appel que lorsqu'elles s'étaient accouplées avec un mâle et l'avaient perdu. En l'absence des mâles, les femelles deC. ugandensis couraient activement pendant plusieurs minutes après l'amputation de leurs ailes, puis prenaient la posture d'appel entre d'autres périodes de déplacement rapide. On nota l'emploi par les femelles deC. ugandensis dans la posture d'appel de ce qui paraissait être un mécanisme défensif contre les petits prédateurs. La présence des ailes n'empêcha pas la pariade chez l'une ou l'autre espèce. Des tandems mâles se voyaient souvent, mais ils étaient presque toujours instables. On n'a vu ni de tandems femelles ni une femelle derrière un mâle. Les tandems ne montraient aucune géotaxie positive et restaient indifférents à la lumière. Les femelles deC. ugandensis tendaient à grimper et redescendre pendant quelques minutes après la pariade. La thigmotaxie était importante dans le choix de l'emplacement du nid chez les deux espèces. Le creusement paraissait dépendre de facteurs extérieurs et ne pas faire partie d'un schéma de comportement. Une fois l'emplacement du nid choisi, les couples redevenaient grégaires, mais ils ne se montraient absolument photonégatifs que lorsqu'ils s'étaient installés dans des cellules. Il y a une discussion sur la plasticité du comportement après le vol.

Zusammenfassung Die Arbeit berichtet über jahreszeitliche und tägliche Flugperioden vonCubitermes ugandensis und vonC. testaceus in Ost-Uganda. Die Untersuchungen wurden fast vollständig im Laboratorium ausgeführt. Geflügelte aus dem Nest genommen waren negativ phototactisch und hielten sich zusammen. Diese Eigenschaften wurden durch den Gebrauch der Flügel ins Gegenteil umgewandelt. Geflügelte flogen nur wenn sie nicht in Gesellschaft mit anderen Termiten des Baues und dem Lichte ausgesetzt waren. Beobachtungen wurden angestellt über Lichtintensität und die Flugfähigkeit vonC. ugandensis. Abwerfen der Flügel wurde in beiden Arten durch Paarung oder Paarungsversuche gefördert, hing aber, zum mindesten inC. ugandensis nicht von solcher Förderung ab. Auf das Abwerfen der Flügel folgte Gleichgültigkeit gegenüber Licht. Künstliche Entfernung der Flügel zeigte, dass beiC. ugandensis der Zusammenhang zwischen Flügelverlust und Verlust positives Phototaxis nicht direkt ist. Der Vorgang des Abwerfens der Flugel wird erörtert. Weibchen beider Arten nehmen im allgemeinen keine Lockstellung ein, bevor sie sich mit einem Männchen gepaart und es verloren hatten. Wenn Männchen fehlen, laufen Weibchen vonC. ugandensis nach Abwerfen der Flügel viele Minuten lebhaft herum, woraufhim zwischen weiteren Perioden lebhaften Laufens die Lockstellung eingenommen wurde. Eine mutmassliche Verteidungsmethode wenn im Lockstellung von Weibchen desC. ugandensis gegen Raubinsekten wurde beobachtet. Das Vorhandensein der Flügel behinderte Paarung in beiden Arten nicht. Männliche Tandems waren häufig, dauerten aber fast nie länger. Weibliche Tandems waren nicht zur Beobachtung, und es wurde nie beobachtet, dass ein Weibchen einem Männchen nachlief. Tandems zeigten keine positives Geotaxis und blieben gleichgültig gegenüber dem Licht. Weibchen vonC. ugandensis pflegten einige Minuten nach der Paarung auf- und abzuklettern. Thigmotaxis, war ein wichtiger Faktor bei beiden Arten in der Wahl eines Platzes für das Nest. Graben scheint von äusseren Faktoren abzuhängen und nicht Teil des Trieblebens zu sein. Der Trieb zur Vergesellschaftung kam mit der Wahl eines Platzes für das Nest wieder, aber deutliche photonegativen Verhalten wurde erst beobachtet, wenn die Paare sich in Zellen eingelebt hatten. Die Plastizität des Verhaltens nach dem Flug wird erörtert.

Summary Information on flight periods and times of flight ofCubitermes ugandensis and ofC. testaceus in eastern Uganda is reviewed. All work was done in the laboratory with the exception of a few field observations on flight. Alates removed from the mound were negatively phototactic and gregarious. These characteristics were reversed by use of the wings. Alates would fly only if free of contact with other termites of the colony and in the presence of light. Observations were made on the flight activity ofC. ugandensis in connection with light intensity. Wing shedding in both species was stimulated by pairing or attempted pairing but, inC. ugandensis at least, was not dependent on such stimulation. Wing shedding was followed by indifference to light. Artificial wing removal demonstrated that inC. ugandensis the connection between loss of wings and loss of positive phototaxis was not a direct one. The method of wing shedding is discussed. Females of both spp. did not generally take up the calling attitude until they had paired with, and lost, a male. In the absence of males,C. ugandensis females would run actively for many minutes after wing shedding, after which the calling attitude was taken up between further periods of active running. An apparent defence mechanism against small predators, used byC. ugandensis females in the calling attitude, was noted. The presence of wings did not inhibit pairing in either species. Male tandems were frequent but nearly always very inconstant. Female tandems were not seen and no female was seen to follow a male. Tandems showed no positive geotaxis and remained indifferent to light.C. ugandensis females tended to climb up and down for some minutes after pairing. Thigmotaxis proved important in nest site selection by both species. Burrowing appeared to be dependent on external factors and not part of a behaviour pattern. Gregariousness returned with selection of the nest site but definite photonegative behaviour was not seen until the pairs were installed in cells. The plasticity of post-flight behaviour is discussed.

Electronic Resource

1420-9098

Springer Online Journal Archives 1860-2000

Biology

Electronic Resource

1432-0428

Insulin-dependent diabetes ; autoimmunity ; BB rat ; insulitis ; 111Indium labelled lymphocytes ; pancreatic imaging

Springer Online Journal Archives 1860-2000

Medicine

Summary Autologous transfusions of 111indium-labelled peripheral blood lymphocytes reportedly image the pancreas of patients with Type 1 (insulin-dependent) diabetes at the time of onset. We attempted to apply this technique to the spontaneously diabetic BB/W rat. First, acutely diabetic BB/W rats, diabetes-prone BB/W rats, diabetes-resistant W-line BB/ W rats, and Wistar Furth rats were given autologous transfusions of labelled peripheral blood lymphocytes. Radioactivity recovered from the pancreas was similar in all groups. No correlation was found between the intensity of imaging and the presence or intensity of insulitis. To decrease non-specific intravascular radioactivity, acutely diabetic, diabetes-prone, and W-line rats were perfused 48 h after autologous transfusion of labelled lymphocytes. Again, the intensity of recovered activity was similar in all groups, using both macroautoradiography and numerical counting techniques. A second set of experiments studied diabetes and insulitis induced by passive transfer of concanavalin A-treated splenic lymphocytes from acutely diabetic donors. Activated lymphocytes were labelled with 111Indium and given to groups of diabetes-prone and diabetes-resistant rats. There were no differences in pancreatic localization 72–96 h after injection. Groups of diabetes-prone and diabetes-resistant rats were also given concanavalin A-activated lymphocytes and then challenged 2–10 days later with autologous transfusions of labelled peripheral blood lymphocytes. Again, no differences in organ labelling or imaging were detected. We conclude that the autologous transfusions of 111indium-labelled lymphocytes do not label or image the pancreas of the BB/W rat.

Electronic Resource