Showing papers by "Lancaster University published in 1981"

Marginal maximum likelihood estimation of item parameters: Application of an EM algorithm.

Abstract: Maximum likelihood estimation of item parameters in the marginal distribution, integrating over the distribution of ability, becomes practical when computing procedures based on an EM algorithm are used By characterizing the ability distribution empirically, arbitrary assumptions about its form are avoided The Em procedure is shown to apply to general item-response models lacking simple sufficient statistics for ability This includes models with more than one latent dimension

Effects of academic departments on students' approaches to studying

Abstract: Summary. 2208 students from 66 academic departments in six contrasting disciplines from British universities and polytechnics completed an ‘approaches to studying’ inventory and a course perceptions questionnaire. Factor analyses of these instruments confirmed the factor structures previously reported. Approaches to studying can be described in terms of three main factors—orientations towards personal meaning, reproducing, and achieving. In the present analysis the final factor split into two: achieving orientation and a factor labelled ‘disorganised and dilatory’ which showed a close relationship with self-rating of academic progress. The course perceptions questionnaire produced two main factors. One described formal teaching methods, vocational relevance, and clear goals and standards, and the other represented a favourable departmental evaluation with the highest loadings on good teaching and openness to students. Subsequent analyses examined links between students' perceptions of their main academic departments and their reported approaches to studying. Departments with highest mean scores on meaning orientation were perceived as having good teaching and allowing freedom in learning. Departments with the highest mean scores on reproducing orientation were seen to have a heavy workload and a lack of freedom in learning. The implications of these statistical findings are discussed in relation to continuing analyses of interview data which clarify the ways in which the organisation of teaching and courses may affect students' approaches to learning.

Ascent and eruption of basaltic magma on the earth and moon

Abstract: The ascent and emplacement of basaltic magma on the earth and moon is modeled by the application of geological and physical observations and constraints. Relatively simple mathematical models of the motion of gas/liquid mixtures are shown to be adequate in the treatment of basaltic eruptions, provided that allowance is made for the coalescence of gas bubbles and that realistic geological and petrochemical constraints are applied to the numerical values of variables. Because gas exsolution from magmas on the earth and moon commonly occur at depths of less than 2 km, it is generally convenient to consider separately the rise of bubble-free magmatic liquid at depth in a planetary crust and the more complex motions occurring near the surface with gas exsolution.

Stimulated recall: a method for research on teaching

Abstract: Summary. A growth in research on teachers' ‘interactive’ thoughts and decision-making has led to the use of the research method of stimulated recall. The method has been employed in a number of different forms, but generally involves the replay of videotape or audiotape of a teacher's lesson in order to stimulate a commentary upon the teacher's thought processes at the time. The appropriate use of the method, the variety of ways in which it has been employed and their advantages and disadvantages are considered together with an examination of the status and validity of recalled thoughts and the problems of interpretation. It is concluded that although questions of validity cannot be completely resolved the technique presents a systematic approach to the collection of data potentially useful in research on teaching.

Volcanism and the dynamics of open magma chambers

Abstract: The repeated eruption of many volcanoes is now accounted for by events taking place in a subterranean magma chamber, which is ‘open’ in the sense that the inflow of material to the chamber from below leads to a magma pressure P which exceeds the lithostatic pressure PL by an amount greater than the tensile strength of the chamber walls (σ) before the contents of the magma chamber have reached thermodynamic and geochemical equilibrium. This is the condition which must be satisfied when an eruption occurs. We have now derived a relationship giving the critical volume of added material (ΔV) required to cause an eruption as a function of magma compressibility and the volume by which the chamber expands.

Factors controlling the distribution of tilia cordata at the northern limits of its geographical range iii. nature and causes of seed sterility

Abstract: SUMMARY Failure of regeneration of Tilia cordata in north-west England is associated with almost complete sterility of the seeds. Between 1964 and 1979 significant numbers of fertile seeds were recorded only after the exceptionally warm summer of 1976. In contrast, large or moderate crops of fertile seed were produced at sites in central and southern England in at least 8 of these years. Comparative studies of pollination, fertilization and seed development at sites in north-west England, central England and northern France show relatively small differences in the proportions of flowers which are pollinated but significant differences in the rates of extension of pollen-tubes. In samples collected in 1977 from north-west England germinated pollen was present on most receptive stigmas but many pollen-tubes extended only a short distance down the style and the few which reached the base appeared to be arrested in the ovary wall. In French samples pollen had germinated on all receptive stigmas and numerous pollen-tubes had reached the ovary within 2 days of pollination. These differences cannot be attributed to variation in the incidence of self-pollination, as at least some trees of T. cordata in northern populations are almost certainly self-fertile. The differences are correlated with temperatures at the time when the samples were collected. When pollen-tubes are growing in sucrose solutions, their rate of extension shows a large response to temperature over the same range (15 to 25°C). Analysis of records shows that temperatures in north-west England at the time of flowering are frequently too low to permit fertilization. This is confirmed by studies of the development of ovules. Although a high proportion of ovules in T. cordata lack embryo sacs, normally at least one is functional in each ovary. In over 90% of fruit formed in north-west England, embryos are contained in none of the 10 ovules. In less than 10% of fruit partly developed embryos are present, suggesting that temperatures are also too low in late summer to allow completion of their development.

The pyroclastic deposits of the 1875 eruption of Askja, Iceland

Abstract: The 1875 explosive eruption of Askja, Iceland was part of a series of regional volcanic and tectonic events which took place in the northern rift zone in 1874 and 1875. These events were marked by regional seismicity, graben formation and a basaltic fissure eruption at Sveinagja, and the plinian eruption of Askja on 28-29 March. Crustal rifting caused basaltic magma to be mixed with rhyolitic magma, triggering the plinian eruption. A caldera, Oskjuvatn, was formed in Askja measuring 3 x 4 km and 267 m deep. Six distinguishable pyroclastic layers can be recognized. The main eruption began with a small sub-plinian pumice eruption forming layer B. The next phase produced a fine-grained, poorly sorted pumice and ash deposit with well developed stratification (layer C), which contains base surge beds near source and is interpreted as phreatomagmatic in origin. The main plinian phase of the eruption lasted 6 h and formed a coarse-grained, poorly bedded pumice-fall deposit (layer D) which contains 75% of the total ejecta. Late-stage explosions formed a layer of lithic clasts (layer E). Isopach and grain-size isopleth maps show that the vents migrated from south to north along a line 1.5 km long in the area now occupied by Oskjuvatn. The intensity and column height of the eruption increased with time as shown by reverse grading and an increasing dispersal index in successive layers. Most of the ejecta is composed of white rhyolitic pumice and ash. Lithics consist of rhyolitic obsidian, partially fused trondhjeimite, and basalt fragments: layer D contains 2.1 mass % lithics. All layers contain abundant grey pumice clasts consisting of intimate mixtures of dark brown basaltic and brown rhyolitic glasses. The mass percentage of mixed pumice in layer D is 4.7, of which 40 % is basaltic glass. These mixed pumice clasts are concentrated at distances of 30-80 km in layer D by aeolian sorting. A grey, crystal-rich, andesitic pumice occurs as inclusions in the white pumice. Layer D shows a systematic decrease in median grain diameter, but no change in cr^ with distance from source. Layer C shows no change in median grain diameter, but a decrease in with distance from source. Phreatomagmatic deposits such as layer C can be readily distinguished from plinian deposits on a Md$ against cr^ diagram, on a against a* (skewness) diagram and on the F against D plot of Walker (1973). The downwind, coarse-tail grading in layer C is attributed to fall-out of fine ash as clumps and aggregates. The total grain-size distributions of both layers D and C show bimodality. In layer D a minor mode in the ash size classes reflects secondary processes of fragmentation by collisions in the vent and column, whereas the major mode is due to disruption of magma by expanding gases. In layer C the fine mode is dominant and represents extensive fragmentation by explosive interaction with water. Field and grain-size studies of layer D show that impact breakage is of major importance near source.

Nonequilibrium theory of dirty, current-carrying superconductors: phase-slip oscillators in narrow filaments near T c

Abstract: General equations for the dynamic behavior of dirty superconductors in the Ginzburg-Landau regime T c-T ≪ T care derived from microscopic theory. In the immediate vicinity of T ca local equilibrium approximation leads to a simple generalized time-dependent Ginzburg-Landau equation. The oscillatory phase-slip solutions presented previously are discussed in greater detail.

Biochemical explanations of more than additive inhibitory effects of low atmospheric levels of sulphur dioxide plus nitrogen dioxide upon plants

Abstract: SUMMARY Three clones of Lolium perenne L. known to show different sensitivities to SO2 pollution, together with other grasses (Dactylis glomerata L., Phleum pratense L. and Poa pratensis L.), were fumigated with low levels of SO2, NO2 and SO2+ NO2. Ratios of glutamate dehydrogenase activity (GDH) to that of glutamine synthetase (GS) were significantly raised by SO2 (6·8 parts 10-8 for 11 weeks) or SO2+ NO2 in the SO2-sensitive cloned cultivar S23 of L. perenne and by SO2+ NO2 in cloned Lolium perenne material which has high resistance to SO2 (S23 Bell resistant). In Lolium derived from Pennine upland (Helmshore clone) GDH/GS ratios were unchanged in the presence of SO2 or SO2+ NO2 but all three clones showed slight elevations in ratios in response to NO2 fumigation alone. Within a week after treatment with NO2, all grasses had significantly higher nitrite reductase activities than similar plants given clean air, SO2 or SO2+ NO2 treatments. The presence of SO2 appeared to destroy the ability of the plant to respond to NO2, and this inhibition of a potential detoxification mechanism of nitrite is believed to be one of the main reasons why the SO2+ NO2 combination exhibits more than additive effects upon the growth of grasses. All three clones of Lolium perenne and also Phleum pratense showed enhanced ATP formation in the presence of low (6·8 parts 10-8 for 20 weeks) levels of NO2, but reduced cyclic photophos-phorylation in the presence of either SO2 or SO2+ NO2. At higher levels of shorter duration (25 parts 10-8 for 11 days), rates of ATP formation, ATP content and energy charge ratios were higher in NO2 fumigated tissue than in controls, but lower in SO2+ NO2 treated tissue, although basic electron transport systems were unaffected. It is believed that the principal effect of the pollutant combination is upon proton gradients within the photosynthetic membranes leading to general deficiency in ATP which is necessary both for growth and the repair of secondary pollutant damage elsewhere. Parts 10-8 (parts per hundred million) = quantity in μ m-3× (1/mol. wt × 106) × 0·0224 × 108 at s.t.p. * for 11 weeks) or SO2+ NO2 in the SO2-sensitive cloned cultivar S23 of L. perenne and by SO2+ NO2 in cloned Lolium perenne material which has high resistance to SO2 (S23 Bell resistant). In Lolium derived from Pennine upland (Helmshore clone) GDH/GS ratios were unchanged in the presence of SO2 or SO2+ NO2 but all three clones showed slight elevations in ratios in response to NO2 fumigation alone.

Implementation of computer simulation projects in health care.

Abstract: In a survey of computer simulation in health care, few projects were found which reported any success in implementing their results. These few studies have been examined in detail to evaluate the success of their implementation and extract possible reasons for it by comparing these studies with the many unsuccessful ones. Discussion includes the criteria for selecting potentially successful projects before they are started and the reasons why health care is a particularly difficult area for implementation.

A Note on the Regression Analysis of Censored Data

Abstract: Maximum likelihood estimates of the parameters in linear models with censored normal responses may be simply obtained using the EM algorithm. The iterative computations required for the regression coefficients are identical to those described by Schmee and Hahn for least squares estimates, but those for the variance estimates are different. The biases of the two variance estimates are discussed.

A Psychological Approach to Research on Teachers' Classroom Decision‐making

Abstract: A number of different approaches to research on teachers' classroom decision-making have developed over recent years. This paper outlines a psychological approach, and points out that several exploratory studies of teachers' thoughts and decision-making indicate that, in the classroom, teachers rarely make decisions in the sense of making choices amongst alternatives at all. It would appear instead that they respond in a rule-fashioned manner to particular configurations of cues, many of which concern attributes of their pupils. In addition, decision-making research suggests that several commonly found classroom interaction patterns serve managerial, as opposed to instructional, functions. Whether this is due to inadequacies of the research methods and research designs employed or to the very nature of teaching is problematic. However, differences found between experienced and probationer teachers in both cognitive and behavioural variables would suggest that decision-making research may make a useful contribution to teacher training.

A comparative study of protein composition in the chitin-protein complexes of the beak, pen, sucker disc, radula and oesophageal cuticle of cephalopods

Abstract: 1 1 Chitin-protein complexes from a variety of cephalopod tissues show a surprisingly wide range of composition both in terms of the chitin-protein ratio and the composition of the protein 2 2 Comparisons are made between the amino acid compositions of these and related chitin-protein complexes in terms of parameters such as polar content, hydrophobicity and conformational potential 3 3 The sucker disc of Octopus , a structure not previously identified as chitinous, is shown to contain chitin by chemical and physical methods

Effects of urban air pollution on plant growth

Abstract: It is not surprising that effects of air pollutants on plants have been investigated in more detail in rural than in urban situations, because the economic implications for agriculture and forestry are of more widespread concern than the fate of plants of amenity value. Apart from areas near well defined sources of pollution, such as factories located in the countryside, amounts of pollution are usually less in rural than in urban areas. The types of pollutants experienced are not, however, totally different in nature. A recent survey by Martin & Barber (1980) has, for example, shown that at a rural site in England remote from known sources of pollution, nitrogen oxides (nitric oxide and nitrogen dioxide, collectively known as NO,) occur alongside SO, and 0,, and that there are approximately equal amounts of NO and NO,. The latter are usually considered to be urban pollutants, related to the density of road traffic, but Martin & Barber found that their concentration in the countryside exceeded that of SO, by 50 per cent. Experiments designed to assess the effects of long-term exposures to individual pollutants at concentrations characteristic of rural areas have produced conflicting results, as revealed by a recent review of effects of SO, on grasses (Bell, 1981). On

Teaching styles and pupil progress: a re‐analysis

Abstract: Summary. The object of the study was to examine the statistical techniques available for the analysis of process-product studies involving non-randomised quasi-experimental designs, and to demonstrate the practical effects of their use on the data from the Teaching Styles study (Bennett, 1976). Of particular concern were the ‘unit of analysis’ or aggregation problem, and the differential effects of treatment grouping by cluster and factor methods. The original grouping of teachers into formal, informal and mixed styles was investigated using a latent class model for the 38 binary questionnaire items. Convincing evidence of three overlapping latent classes was found. The comparison of latent classes in terms of pre-test gain scores was examined using a series of variance component models, allowing for correlation of children within the same class. Differences among classes were altered by the probabilistic clustering of the latent class model compared to the original findings, and the significance of the differences was reduced when the correlation among children was allowed for.

Perceived Earnings Functions and Ex Ante Rates of Return to Post Compulsory Education in England.

Abstract: This article offers a direct empirical test of one of the main tenets of the human capital model. It shows that by the end of their compulsory education English pupils in general are aware of the relationship between educational qualifications and average earnings. For the first time in Britain direct calculations are made of ex ante perceived rates of return to upper secondary and higher education. The perceived rates correspond closely to the actual rates estimated by earlier studies. The article also provides useful evidence of differences between social classes and ability groups. In particular it shows that the human capital model offers a much less satisfactory explanation of the behaviour of low ability and working class pupils than it does of high ability and middle class pupils.

Root growth and water relations of oak and birch seedlings.

Abstract: First year seedlings of English oak (Quercus Cobur) and silver birch (Betula pendula) were subjected to pressure-volume analysis to investigate the water potential components and cell wall properties of single leaves. It was hoped that this rapid-drying technique would differentiate between reductions in plant solute potential resulting from dehydration and the effects of solute accumulation.Comparison of results from these experiments with those of slow drying treatments (over a number of days) with plants growing in tubes of soil, indicated that some solute accumulation may have occurred in drying oak leaves. High leaf turgor and leaf conductance were maintained for a significant period of the drying cycle. Roots of well-watered oak plants extended deep into the soil profile, and possibly as a result of solute regulation and therefore turgor maintenance, root growth of unwatered plants was greater than that of their well-watered counterparts. This was particularly the case deep in the profile. As a result of deep root penetration, water deep in the soil core was used by oak plants to maintain plant turgor, and quite low soil water potentials were recorded in the lower soil segments.Root growth of well-watered birch seedlings was prolific but roots of both well-watered and unwatered plants were restricted to the upper part of the profile. Root growth of unwatered plants was reduced despite the existence of high soil water potentials deep in the profile. Shallow rooting birch seedlings were unable to use this water.Pressure-volume analysis indicated that significant reductions of water potential, which are required for water uptake from drying soil, would occur in oak with only a small reduction in plant water content compared to the situation in birch. This was a result of the low solute potential in oak leaves combined with a high modulus of elasticity of cell walls. Deep rooting of oak seedlings, combined with these characteristics, which will be particularly important when soil deep in the profile begins to dry, mean that this species may be comparatively successful when growing on dry sites.

Lead in the atmosphere

Abstract: There are two very important reasons for studying lead in air. Firstly, inhaled lead may pass via the respiratory system to the bloodstream and hence contribute to the lead exposure of the population. Secondly, airborne lead is progressively removed from the atmosphere by wet and dry deposition processes causing contamination of other environmental media.

Plutonium transport to and deposition and immobility in Irish Sea intertidal sediments

Abstract: The deposition and possible mobility of plutonium in sediments contaminated by nuclear fuel reprocessing wastes are of considerable importance in assessing the short- and long-term fate of this pollutant. Previous studies have shown that marine sediments very effectively and quickly remove plutonium1, and have suggested both immobile2 and mobile2,3 behaviour of plutonium after deposition. Here, the deposition characteristics and lack of vertical migration of plutonium isotopes in intertidal sediments of the Irish Sea, which are contaminated with radioactive wastes from the Windscale reprocessing facility, are discussed.