Showing papers by "University of Sussex published in 1986"
TL;DR: Rats were tested in place finding tasks in a rectangular environment with distinct featural panels in the corners and it was theorized that in orienting in space by using landmarks, the rat uses primarily a purely geometric module, which also serves as a basis for coordinating the locations of non-geometric data.
1,051 citations
TL;DR: The high-frequency limit of phase-locking has been measured in fibres of the auditory nerve in the guinea-pig and it is shown that phase- locking begins to decline at about 600 Hz and is no longer detectable above 3.5 kHz.
604 citations
TL;DR: HOGas discussed by the authorsE et al. as discussed by the authors found that 3-6-year-old children were either put into real-life situations or were read stories in which another person or story character was excluded from certain information.
Abstract: HOGREFE, G.-JUERGEN; WIMMER, HEINZ; and PERNER, JOSEF. Ignorance versus False Belief: A Developmental Lag in Attribution of Epistemic States. CHILD DEVELOPMENT, 1986, 57, 567-582. 3-6-year-old children were either put into real-life situations or were read stories in which another person or story character was excluded from certain information. Their competence in attributing absence of knowledge (ignorance) was compared to their competence in attributing a false belief to the other. A marked difference between attributions was found. In a transitional stage at 3-4 years children were able to attribute ignorance but failed to attribute the resulting false belief. The same developmental gap for children about 2 years older was found between the attribution of secondorder ignorance and second-order false belief. Results are interpreted to show that children at a transitional stage find it difficult to represent the incompatible propositions describing the true state of affairs and the state of affairs falsely believed to be true by the other. Such a complexity is not involved in the understanding of ignorance where it has just to be represented that the other does not share the representation of the true state of affairs.
584 citations
TL;DR: This article starts by presenting a fairly idiosyncratic view of teaching programming which makes use of mechanistic analogies and points out some of the pitfalls and goes on to examine certain errors based on the misapplication of analogies as well as certain interaction errors.
Abstract: This article is a brief introduction to some of the issues that teachers of programming may find helpful. It starts by presenting a fairly idiosyncratic view of teaching programming which makes use of mechanistic analogies and points out some of the pitfalls. The article goes on to examine certain errors based on the misapplication of analogies as well as certain interaction errors. The main emphasis is on the notional machine both at the general level of understanding (and misunderstanding) the relationship of the terminal to the computer as such, as well as at the more specific level of understanding assignment. Notation and mistakes that poorly-designed languages can induce novices to commit are discussed.
526 citations
TL;DR: In this article, the results obtained by applying the method of stochastic averaging to random vibration problems are discussed and applied to a variety of problems involving the response of lightly damped systems to broad-band random excitations.
Abstract: Results obtained by applying the method of stochastic averaging to random vibration problems are discussed. This method is applicable to a variety of problems involving the response of lightly damped systems to broad-band random excitations. Solutions pertaining to both linear and non-linear vibrations are reviewed, and it is shown that the technique enables, in the case of parametric excitation, stability criteria to be established. Some results which have been obtained relating to the first-passage reliability problems are also surveyed. Various applications of the theory to engineering problems are outlined.
490 citations
TL;DR: HindIII and SmaI sites within the KmR gene have been removed so that all of the cloning sites in the multi-linker region of these plasmids may be used except the AccI site.
459 citations
TL;DR: It is demonstrated here that nitrogen fixation by this strain depends on vanadium and it is shown that its purified nitrogenase is a binary system in which the conventional molybdoprotein is replaced by a vanadoprotein.
Abstract: The requirement for molybdenum in biological dinitrogen fixation, first reported by Bortels1, is due to its involvement at or near the site of reduction of N2 in conventional nitrogenase. To date, all nitrogenases which have been purified to homogeneity consist of an iron protein (component 2) and a molybdoprotein (component 1)2. Azotobacter vinelandii, an obligately aerobic diazotrophic bacterium, has two systems for nitrogen fixation: a conventional nitrogenase involving molybdenum and an alternative system which functions under conditions of Mo deficiency and does not require the structural genes for conventional nitrogenase3–6. The properties of the nitrogenase in extracts of comparable deletion strains of A. vinelandii are consistent with a two-component system6,7 in which the component 1-containing fraction has no detectable Mo (ref. 6). Recently, an alternative nitrogen fixation system has been demonstrated in Azotobacter chroococcum strain MCD1155, in which the structural genes for conventional nitrogenase are deleted8. We demonstrate here that nitrogen fixation by this strain depends on vanadium and we show that its purified nitrogenase is a binary system in which the conventional molybdoprotein is replaced by a vanadoprotein.
431 citations
TL;DR: In this paper, a theory is developed which calculates the positions of unbound mode index dark lines in planar waveguide systems, by means of evaluating the surface reflectivity at the coupling prism.
Abstract: A theory is developed which calculates the positions of unbound mode index dark lines in planar waveguide systems, by means of evaluating the surface reflectivity at the coupling prism. This method is shown to explain some extra observed dark mode lines which are not predicted by other theories. Values calculated for typical ion-implanted waveguide profiles are compared favourably with those obtained from other approximations.
371 citations
01 Jun 1986-Journal of Comparative Physiology A-neuroethology Sensory Neural and Behavioral Physiology
TL;DR: The aim of this study is to understand what a rodent learns about the geometrical relations between a goal and nearby visual landmarks and how it uses this information to reach a goal, and concludes that a gerbil's representation of its environment is complete.
Abstract: 1.
The aim of this study is to understand what a rodent (Meriones unguiculatus) learns about the geometrical relations between a goal and nearby visual landmarks and how it uses this information to reach a goal. Gerbils were trained to find sunflower seeds on the floor of a light-tight, black painted room illuminated by a single light bulb hung from the ceiling. The position of the seed on the floor was specified by an array of one or more landmarks. Once training was complete, we recorded where the gerbils searched when landmarks were present but the seed was absent. In such tests, gerbils were confronted either with the array of landmarks to which they were accustomed or with a transformation of this array.
2.
Animals searched in the appropriate spot when trained to find seeds placed in a constant direction and at a constant distance from a single cylindrical landmark (Fig. 1). Since gerbils look in one spot and not in a circle centred on the landmark, the direction between landmark and goal must be supplied by cues external to the landmark array. Distance, on the other hand, must be measured with respect to the landmark. Tests in which the size of the landmark was altered from that used in training suggest that distance is not learned solely in terms of the apparent size of the landmark as seen from the goal (Fig. 3).
3.
Gerbils can still reach a goal defined by an array of landmarks when the room light is extinguished during their approach (Figs. 4, 5). This ability implies that they have already planned a trajectory to the goal before the room is darkened. In order to compute such a trajectory, their internal representation of landmarks and goal needs to contain information about the distances and bearings between landmarks and goal.
4.
For planning trajectories, each landmark of an array can be used separately from the others (Fig. 7). Gerbils trained to a goal specified by an array of several landmarks were tested with one or more of the landmarks removed or with the array expanded. They then searched as though they had computed an independent trajectory for each landmark. For instance, gerbils trained with an array of two landmarks were tested with the distance between two landmarks doubled. The animals then searched for seeds in two positions, which were at the correct distance and in the right direction from each landmark.
5.
If an internal representation of an array of landmarks is to be used to plan a trajectory, landmarks seen on the ground must be matched to those held in memory. One way in which gerbils do this is by learning properties of individual landmarks, such as their shape, size or surface markings (Figs. 10, 11, 13). For example, gerbils were able to locate seeds defined by a single relevant landmark while ignoring an irrelevant landmark with different features which was placed randomly with respect to the goal.
6.
Several experiments (Figs. 4, 12, 13, 14) suggested that, although landmarks may be used independently for computing trajectories, the process of matching landmarks to the gerbil's representation requires a knowledge of the distances and directionsbetween landmarks.
7.
We conclude that a gerbil's representation of its environment is complete in that it stores explicitly or can compute from what it has stored the geometric arrangement of landmarks and goal. We discuss the possibility that its spatial memories consist of a set of vectors describing the distance and direction from the goal to each landmark (Fig. 18) and consider the advantages and disadvantages of such a goal-centred memory.
341 citations
TL;DR: It is shown that the positioning and orientation of the upstream sequence is not critical for promoter activity up to a distance of 2 kilobases (kb) and that the upstream sequences is itself transcriptionally inactive, probably acting in cis with the downstream sequences to produce a fully active promoter.
Abstract: Nitrogen fixation (nif) genes in Klebsiella pneumoniae are controlled by a transcriptional activation mechanism which requires the ntrA gene product acting concert with either the ntrC or nifA products (reviewed in ref. 1). The nif promoters lack the canonical −35, −10 promoter elements and instead their activation requires nucleotide sequences located around −24 and −12 (refs 2–4). We have now identified and characterized a further essential promoter sequence in the K. pneumoniae nifH, nifU, nifB and ORF promoters, located more than 100 base pairs (bp) from the transcription start site. This promoter element is required for nifA- but not ntrC-mediated activation and for the inhibition of chromosomal nif expression observed when cells harbour multiple copies of certain nif promoters5. The upstream sequence is conserved among 10 Rhizobium and 2 Azotobacter nif promoters. We show that the positioning and orientation of the upstream sequence is not critical for promoter activity up to a distance of 2 kilobases (kb) and that the upstream sequence is itself transcriptionally inactive, probably acting in cis with the downstream sequences to produce a fully active promoter. Thus, an extended promoter structure is required for nif gene expression.
295 citations
TL;DR: Analysis of relationships between brain size and differences in ecology and behavior within the order Carnivora finds significant differences in brain size exist among families, compared with those found in small mammals, primates and bats.
Abstract: This paper examines relationships between brain size (relative to body size) and differences in ecology and behavior within the order Carnivora. After removing the effects of body size (either body weight or head and body length) significant differences in brain size exist among families. Variation in relative brain size across the order and comparative brain size within families might relate to differences in diet (carnivores and omnivores have larger brain sizes than insectivores) and breeding group type. These findings are discussed and compared with those found in small mammals (rodents, insectivores, lagomorphs), primates and bats.
TL;DR: It is proposed that the responses of inner and outer hair cells are consistent with sensory and motor roles respectively in mechanoelectric transduction and that the outerhair cells are the site of an active mechanical process responsible for the frequency selectivity and sensitivity of the cochlea.
TL;DR: A DNA fragment called suc1 has been found to rescue cells mutated in the cell cycle control gene cdc2 of the fission yeast Schizosaccharomyces pombe, suggesting that it interacts directly with the cDC2 gene function.
Abstract: A DNA fragment called suc1 has been found to rescue cells mutated in the cell cycle control gene cdc2 of the fission yeast Schizosaccharomyces pombe. The suppressing activity of suc1 is observed when it is present on a multicopy number plasmid. The gene does not hybridise to cdc2 and maps elsewhere in the genome. Its effect is cdc2 allele specific suggesting that it interacts directly with the cdc2 gene function.
TL;DR: In this article, it was shown that T ∼ ω −1 log { l ( h mω ) 1 2 } for sojourn in the region | x | l, where l is the resolving power of the detector.
TL;DR: The authors pense generalement que tous les univers fermes S 3 en expansion, qui verifient les conditions d'energie standard, s'effondrent a nouveau vers une seconde singularite.
Abstract: On pense generalement que tous les univers fermes S 3 en expansion, qui verifient les conditions d'energie standard, s'effondrent a nouveau vers une seconde singularite. On montre que c'est faux, meme pour des univers de Friedmann
TL;DR: Development programs in refugee-affected areas and refugee studies will do a disservice if they neglect adverse effects of refugees on vulnerable hosts, which further strengthen the case for development to benefit the whole population in refugee -affected areas.
Abstract: Refugee relief organizations and refugee studies have refugees as their first concern and focus. Adverse impacts of refugees on hosts are relatively neglected. When impacts are considered, they are...
TL;DR: In this article, the conditions for and consequences of F -spin symmetry are investigated and closed expressions for the following properties are given: the excitation energies; the M 1, E 2, and M 3 excitation strengths from the ground state to all 1 +, 2 +, and 3 + states, the decay of the nonsymmetric 1 + and 2 + states; and the dipole and quadrupole moments of maximal F-spin states.
TL;DR: Asymmetric responses of this type provide additional evidence that lateralization of function in the brain, long thought to be a uniquely human phenomenon, is widespread among vertebrates.
TL;DR: A plasmid vector, pJBS633, that facilitates the construction of translational fusions of genes of interest to the coding region of the mature form of TEM beta-lactamase has been developed and should be useful as a general vector for the construction and analysis of protein export signals and the determination of the organisation of proteins in the E. coli cytoplasmic membrane.
TL;DR: The gene suc1 encodes a product which suppresses certain temperature sensitive mutants of the cell cycle control gene cdc2 of Schizosaccharomyces pombe and may have a regulatory role in these processes.
Abstract: The gene suc1 encodes a product which suppresses certain temperature sensitive mutants of the cell cycle control gene cdc2 of Schizosaccharomyces pombe. Mutants in the suc1 gene or over-expression of its product leads to delays in mitotic and meiotic nuclear division. Deletion of the suc1 gene is lethal and generates some cells blocked in the cell cycle and others impaired in cellular growth. It is likely that the suc1 gene product binds and forms unstable complexes with the cdc2 protein kinase and with other proteins necessary for the cell cycle and cellular growth. suc1 may have a regulatory role in these processes.
TL;DR: It is shown that highly repeated sequences are likely to persist longest when crossing over is infrequent, because unequal exchange among repeated sequences generates single copy sequences, and a population that becomes fixed for a single copy sequence by drift remains in this state indefinitely (in the absence of gene amplification processes).
Abstract: We suggest hypotheses to account for two major features of chromosomal organization in higher eukaryotes. The first of these is the general restriction of crossing over in the neighborhood of centromeres and telomeres. We propose that this is a consequence of selection for reduced rates of unequal exchange between repeated DNA sequences for which the copy number is subject to stabilizing selection: microtubule binding sites, in the case of centromeres, and the short repeated sequences needed for terminal replication of a linear DNA molecule, in the case of telomeres. An association between proximal crossing over and nondisjunction would also favor the restriction of crossing over near the centromere. The second feature is the association between highly repeated DNA sequences of no obvious functional significance and regions of restricted crossing over. We show that highly repeated sequences are likely to persist longest (over evolutionary time) when crossing over is infrequent. This is because unequal exchange among repeated sequences generates single copy sequences, and a population that becomes fixed for a single copy sequence by drift remains in this state indefinitely (in the absence of gene amplification processes). Increased rates of exchange thus speed up the process of stochastic loss of repeated sequences.
TL;DR: This article found that skilled readers engage in more constructive processing and comprehension difficulties are not the result of a defective working memory (SRT) in children with normal word recognition ability, and that comprehension difficulties were not due to a defect in the working memory.
Abstract: Reports on two experiments that explore the comprehension difficulties of children with normal word recognition ability. Concludes that skilled readers engage in more constructive processing and that comprehension difficulties are not the result of a defective working memory. (SRT)
TL;DR: The book points the way to the future indicating what work has to be done to answer the important questions and without doubt is essential reading for those working on these animals.
TL;DR: A class of controllers with integral action is shown to arise directly from appropriate system models via the zero-gain predictor approach, and a corresponding class of hybrid self-tuning controllers are shown to have both integral action in the controller and offset removal in the tuning algorithm.
Abstract: A class of controllers with integral action is shown to arise directly from appropriate system models. Via the zero-gain predictor approach, a corresponding class of hybrid self-tuning controllers is shown to have both integral action in the controller and offset removal in the tuning algorithm. Implementation details and some experimental results are given.
TL;DR: The xylABC promoter (OP1), located on the TOL plasmid of Pseudomonas putida contains sequences homologous to the conserved regions found in nitrogen fixation (nif) promoters and in other promoters subject to nitrogen control.
Abstract: The xylABC promoter (OP1), located on the TOL plasmid of Pseudomonas putida contains sequences homologous to the conserved regions found in nitrogen fixation (nif) promoters and in other promoters subject to nitrogen control. XylA-lac fusions were constructed in order to monitor expression from the OP1 promoter in Escherichia coli. Transcription was activated in the presence of the heterologous regulatory genes ntrC or nifA from Klebsiella pneumoniae as well as by the homologous P. putida regulatory gene xylR. In all cases activation was also dependent on the ntrA gene, whose product has been implicated as a specific sigma factor for ntr activatable operons. The 5′ ends of xylA mRNA, detected by S1 nuclease mapping of in vivo transcripts, were identical in strains containing xylR, ntrC or nifA as transcriptional activators. However, activation of the K. pneumoniae nifL or nifH promoters by xylR was not detected.
TL;DR: In this article, the authors carried out a year-round survey of badger defecation sites in order to assess seasonal and spatial characteristics of site use, and concluded that territoriality in badgers may be related more to defence of oestrus females by resident males than to defense of food resources.
Abstract: Badgers (Meles meles) defecate and scent mark in open pits ('dung pits') which seem to have territorial significance. We carried out a year-round survey of badger defecation sites in order to assess seasonal and spatial characteristics of site use. Our results show that badgers defecate at two different types of site, which we refer to as 'latrines' and 'temporary defecation sites' (TDS's) respectively. Latrines are relatively large aggregations of dung pits (up to 25 separate pits) that are visited year-round; they are largest in spring (April) and autumn (October); they are more numerous around the perimeter of a territory; they are associated with fences and roads; and they often contain anal-gland secretion as well as faeces. TDS's, by contrast, are single dung pits or small aggregations of pits that are used only once or twice and are then abandoned; they are most numerous in mid-winter (December and January); they are scattered throughout the territory both close to and away from fences and roads; and they do not usually contain anal secretion. Spatial and seasonal changes in frequency of TDS's are shown to correlate with food availability and with foraging behaviour, and we conclude that TDS's have no special function beyond elimination of faeces. Latrines, however, do seem to have communicatory significance, and we conclude that they are concerned with territory defence. Since seasonal changes in latrine use correlate more closely with mating than with food availability we suggest that territoriality in badgers may be related more to defence of oestrus females by resident males than to defence of food resources.
TL;DR: Complementation studies showed that normal values of UDS are restored in heterokaryons obtained by fusion of TTD cells with normal and xeroderma pigmentosum (XP)-complementation group A-cells, in contrast the defect is not complemented by fusion with XP-com implementation group D-fibroblasts.
Abstract: We studied the response to UV irradiation in cells from four patients, from three apparently unrelated families, affected by trichothiodystrophy (TTD). They showed all the symptoms of this rare autosomal recessive disorder (brittle hair with reduced sulfur content, mental and physical retardation, ichthyosis, peculiar face) together with photosensitivity. We found a decreased rate of duplicative DNA synthesis in stimulated lymphocytes, reduced survival in fibroblasts, and very low levels of unscheduled DNA synthesis (UDS) in Go lymphocytes and fibroblasts after UV irradiation. Complementation studies showed that normal values of UDS are restored in heterokaryons obtained by fusion of TTD cells with normal and xeroderma pigmentosum (XP)-complementation group A-cells. In contrast the defect is not complemented by fusion with XP-complementation group D-fibroblasts.
TL;DR: A game theory model is used to investigate the existence and form of a stable distribution of body sizes in a population and it is found that a single body size or even a narrow range of sizes cannot be stable.