Showing papers by "University of Warwick published in 1973"

Statistical methods for the analysis of genotype-environment interactions.

Abstract: This is largely a review paper, describing various statistical methods for analysing interactions in general and genotype-environment interactions in particular, and giving nearly 100 references to previous work. The joint regression analysis approach introduced by Yates and Cochran (1938) is considered in some detail; alternatives to regression are discussed, as are various stability parameters. Much work has been done on statistical methods for testing for interactions in general, and this also is reviewed, from Tukey's (1949) one degree of freedom for non-additivity to Milliken and Graybill's (1970) generalisation to testing for various types of possible interaction. The difficulties of testing and inference in the presence of interaction are discussed. Data from a two-way table may be regarded as a multivariate set, as first shown by Williams (1952) and later extended by others, particularly Mandel (1969b and 1971 ). These methods are only just beginning to be used in studies of genotype-environment interactions, and several recent references are given. External measurements may be used to measure the environment and these may be either physical or biological. Again, the appropriate methods of analysis are fairly new. The interpretation of interactions is considered in relation to the use to be made of the results. It is suggested that various multivariate techniques may be used to assist in the elucidation of interactions, especially when these are not easy to explain by simpler methods of analysis.

Deterministic one-counter automata

Abstract: The equivalence problem for deterministic one-counter automata is shown to bedecidable. A corollary for schema theory is that equivalence is decidable for Ianov schemas with an auxiliary counter.

The Effect of Shear Stress on the Screw Dislocation Core Structure in Body-Centred Cubic Lattices

Abstract: The behaviour of the ½ a screw dislocation core in the presence of an external shear stress on {110} planes has been studied for a variety of effective interionic potentials, each representing a stable b. c. c. lattice. The distortion and motion of the core are described using the concept of fractional dislocations, which are imperfect dislocations bounding a ribbon of generalized (unstable) stacking fault. Three essentially distinct types of movement are found, and the relation of these to plastic flow and twinning in real b. c. c. metals is discussed. It is found that the movement of the dislocation core can be rationalized in terms of the relative stresses needed to create generalized stacking faults on {110} and {112} planes.

Comparative studies of model reference adaptive control systems

Abstract: A brief but up-to-date survey on existing methods of designing a class of model reference adaptive control systems is given in this paper. A comparison of the merits of the various design rules is also made with particular attention to the M.I.T. rule and the Lyapunov synthesis technique. Subsequently a systematic performance comparison of the various designs, with deterministic as well as stochastic inputs, is presented using the computer simulation studies of two simple gain adjustment schemes. From the dimensionless characteristic graphs obtained the Lyapunov schemes are found to exhibit superior performance over other designs. These graphs also uncover the strange adaptive response of those designs based on gradient methods in that the performance index may increase or decrease with increasing system gain parameters.

Ribonucleic acid synthesis in chloroplasts.

Abstract: Chloroplasts isolated from young spinach leaves incorporate [3H]uridine into RNA. This incorporation shows an absolute requirement for light and does not occur in lysed chloroplasts. Fractionation by polyacrylamide-gel electrophoresis of the RNA synthesized in vitro reveals a major discrete product of molecular weight 2.7×106 and two minor products of molecular weight 1.2×106 and 0.47×106. These discrete products are super-imposed on a background of polydisperse RNA. The incorporation of 32Pi into chloroplast rRNA species (mol.wt. 1.05×106 and 0.56×106) in excised spinach leaves proceeds after a distinct lag period compared with the incorporation into cytoplasmic rRNA species (mol.wt. 1.34×106 and 0.7×106). Incorporation of 32Pi into chloroplast RNA species of molecular weight 2.7×106, 1.2×106, 0.65×106 and 0.47×106 proceeds without such a time-lag. The kinetics of labelling of the individual RNA components is consistent with the rapidly labelled RNA species of molecular weight 1.2×106 and 0.65×106 being precursors to the more slowly labelled rRNA species of molecular weight 1.05×106 and 0.56×106 respectively.

A Bayesian method for histograms

Abstract: SUMMARY This paper describes a Bayesian procedure for the simultaneous estimation of the proba- bilities in a histogram. A two-stage prior distribution is constructed which assumes that probabilities corresponding to adjacent intervals are likely to be closely related. The method employs multivariate logit transformations, and a covariance structure similar to that assumed in the first-order autoregressive process. Posterior estimates are obtained which combine information between the intervals and have the practical effect of smoothing the histogram. A weakness of the Bayesian approach has been its inability to cope with independent observations whose common distribution is not restricted to any particular family. We seek to remedy this deficiency by providing a technique for the analysis of n observations, which are assumed independent and identically distributed with unknown density q(y) which is concentrated on a finite interval I of the real line. We will assume that q(y) is thought a priori to possess a continuous first derivative for all y eI, or to possess some similar property of smoothness. We are posed with the problem of how to obtain estimates for q(y) and its moments which take account of this prior informa- tion. The problem will be treated by using a histogram to approximate q(y), and by esti- mating the probabilities in the histogram under the assumption that they are related in a certain manner. A disadvantage of our method is that the histogram estimate for q(y) will be discontinuous at several points in 1, and will not usually satisfy the smoothness property assumed a priori for the theoretical density. However, we hope that this will to some extent be compensated for by the advantages of the estimation procedure proposed for the probabilities in the histogram. Good & Gaskins (1971) and Boneva, Kendall & Stefanov (1971) provided sampling theory methods for the estimation of a density. An advantage of a Bayesian approach is that it takes proper account of the prior information, since the latter may be incorrectly emphasized when basing the analysis on intuitive ideas. Our method will be fairly flexible in allowing information about the degree of smoothness, and the shape, of the density to be incorporated into the prior model.

Changes in the numbers of viable weed seeds in soil under different regimes

Abstract: Summary. In a 4-year experiment with a naturally-occurring population of viable weed seeds, the numbers in the top 23 cm of soil decreased exponentially in the absence of further seeding. The rates of loss were very similar on undisturbed plots which were left bare (34% per year), mulched with farmyard manure (31%) or grassed down (32%). On plots dug twice a year in March and September, the loss was 42% per year, and with frequent cultivation (dug seven times a year) it was 56% per year. The numbers of seedlings in any one year on plots dug twice a year represented approximately 6% of the viable seeds present at the start of the year. Variations du nombre de semences viables de mauvaises herbes dans le sol selon differents regimes Resume. Au cours d'une experience poursuivie pendant 4 ans avec une population naturelle de semences viables de mauvaises herbes, leur nombre dans les 23 premiers cm du sol a decru exponentiellement en I'absence de semis ulterieur. Les taux de diminution furent tres voisins dans des parcelles non travaillees, en terrain nu (34% par an), dans des parcelles paillees avec du fumier de ferme (31%) ou enherbees (32%). Sur les parcelles travaillees deux fois par an, en mars et en septembre, la diminution fut de 42% par an, avec des facons culturales frequentes (sept fois par an), elle fut de 56% par an. Le nombre des plantules au cours dc chaque annee sur les parcelles travaillees deux fois par an representa approximativement 6% du nombre des semences viables presentes au debut de I'annee. Zahlenmasige Veranderungen der lebensfahigen Unkrautsamen im Boden bei verschiedenen Behandlungen Zusammenfassung. In einem vierjahrigen Versuch mit oiner naturlichen Population von lebensfahigen Unkrautsamen nahm die Zahl in den obersten 23 cm des Bodens exponentiell ab, wenn das Aussamen der Unkrauter verhindert wurde. Die Verlustraten in unbewachsenen, unbearbeiteten Parzellen (34% je Jahr), waren denen in mit Stallmist gedungten (31%), oder denen mit Gras bewachsenen (32%), sehr ahnlich. In Parzellen, die jahrlich zweimal, im Marz und September, umgegraben wurden, betrug der Verlust 42% je Jahr. Bei wiederholter Bearbeitung (siebenmal pro Jahr umgegraben), belief sich der Verlust je Jahr auf 56%. In den Parzellen die zweimal jahrlich umgegraben wurden, betrug die Zabl der Keimlinge ungefahr 6% der lebensfahigen Samen, die bei Beginn des Jahres vorhanden waren.

Studies on energy-linked reactions. Genetic analysis of oligomycin-resistant mutants of Saccharomyces cerevisiae.

Abstract: The genetics of the two major phenotypic classes of oligomycin-resistant yeast mutants have been investigated. All the class II mutants (oligomycin specific) tested show typical cytoplasmic inheritance and the determinants appear located on mtDNA. Evidence is presented that this type of resistance can be conferred by at least two distinct groups of nonallelic cytoplasmic determinants. The class I mutants which show cross resistance to a variety of inhibitors and uncouplers of energy conservation reactions exhibit behaviour on genetic analysis which is not fully understood. Tetrad analysis indicates that a nuclear gene is concerned but many anomalous observations, discussed here, suggestive of the involvement of a cytoplasmic element remain to be explained.

On the stability of nonlinear cold plasma waves. Part 2

Abstract: In part 1 (Infeld 1972), it was shown that a nonlinear stationary wave in a cold plasma is marginally stable to all perturbations that are functions of the spatial direction parallel to the direction of propagation only. The stability analysis is extended here in part 2 to include general spatial variations. Within the limitations of the treatment, it is found that, for wave amplitudes up to maximal value (onset of trapping), the wave is marginally stable. Hence one would expect these large-amplitude cold plasma waves to exist in practice.The one-dimensional analysis of part 1 is also extended to include waves with relativistic velocities, and such waves are again found to be marginally stable.

Studies on relationship between water regime and flavour strength in watercress (Rorippa nasturtium-aquaticum (L) Hayek), cabbage (Brassica oleracea capitata) and onion (Allium cepa)

Abstract: SummaryGrowth of certain vegetables under conditions of water stress has been shown to lead to increased flavour strengths. Watercress was grown in sand-compost mixtures in a glasshouse with three different water regimes. One group was maintained at approximately pot capacity by addition of a nutrient solution, in a second the solution was withheld until the incipient wilting point was reached, and the third group was intermediate between the other two. Cabbages and onions were grown in the field under moveable transparent shelters with two different water regimes. Flavour was determined gas chromatographically and by sensory and other methods. As determined by means of βphenylethyl isothiocya-nate peak areas, the overall range of watercress flavour strength was 6.4-fold. The corresponding values for cabbages and onions were 3.8-fold and 3.9-fold, respectively, based on gas-chromatographic headspace total peak areas. These ranges were relatively small as compared with corresponding changes at extremes of ...

Electric fail-safe actuator

Abstract: An electrically operated fail-safe valve actuator employs a spring which is wound to store energy during operation of the electric drive motor, an electric clutch operable to disengage the drive motor from the actuator output shaft in response to loss of power from the electrical supply whereby the spring drives the valve in the opposite direction.

The analysis of variation between and within genotypes and environments.

Abstract: Methods of analysing variation between and within genotypes and environments are discussed. Principal component analysis, or an equivalent technique proposed by Mandel (1971) for examining interactions in two-way tables, is suggested as an appropriate method in many circumstances, followed by analysis of variance on these principal components for replicated data. Various techniques are applied to yields of carrots from a trial in which eight varieties were grown in 34 environments representing a set of 17 site/year combinations at two densities. The largest source of variation within genotypes is found to be that between environments but not conversely. Two other sources of variation are identified within genotypes and environments, one representing the interaction of varieties with site/year effects and the other their interaction with densities. Analysis of variance indicates the varieties and environments contributing to these interactions. The general implications of the use of principal component analysis are discussed, particularly in situations such as that with the carrot data where the method of joint regression analysis fails because the genotype-environment interaction contains more than one independent component.

Fashion Forecasting for a Mail Order Company Using a Bayesian Approach

Abstract: Traditional forecasting methods assume a large amount of product history. New product launches take place in the absence of any product sales statistics and initially it is necessary to formulate beliefs as to the product future and then to combine these with sales data as it becomes available. The particular situation considered in this paper concerns a mail order company which sells a different group of ladies dresses on each of its catalogues. The life of a catalogue is of the order of 6 months and material ordering decisions tend to be relevant only at the beginning and during the first few weeks of the catalogue. The task of the Distribution Department is not helped by the presence of a large number of returns from customers. This paper describes a Bayesian approach to the forecasting problem and the "live" performance of the method on one catalogue is discussed.

Further studies on seed transmission in the ecology of some aphid-transmitted viruses.

Abstract: SUMMARY A small proportion (1–4%) of the seeds of Stellaria media extracted from fallow soil from three widely separated areas contained cucumber mosaic virus (CMV). S. media seeds buried for 21 months produced 5 % infected seedlings. S. media plants from Britain, N. America and Australia were least severely affected by the CMV strain obtained from their country of origin and showed more severe reactions when infected with two alien strains. Several weed species were experimentally infected with lettuce mosaic, turnip mosaic and cauliflower mosaic viruses but, although virus was detected in the seeds of some species, it was not transmitted to any of their seedlings.

Some Effects of Weed Competition on the Growth of Onions

Abstract: SummaryIn competition with annual weeds (160–230/m2) the photosynthetic capacity and consequent bulb size of onion plants were greatly reduced. Growth was depressed, leaf-blade production was delayed and fewer leaves were formed; the latter were smaller, contained less chlorophyll and died more rapidly than those of the weed-free crop. When weeds were removed 7½ weeks after 50% crop emergence, there was little subsequent increase in dry weight or bulb size and only one or two further small foliage leaves were produced. By this time the dry weight of weeds per unit area was twenty times that of the crop, and about half the applied nitrogen and a third of the potassium had been taken up by the weeds. The results indicate that the severe effects of weeds on onions are associated with an initial competitive disadvantage of slow crop growth, while the limited duration of the vegetative phase prevents recovery when the weeds are removed after competition has begun.

The early relative growth rates of six lettuce cultivars as affected by temperature

Abstract: SUMMARY Six lettuce cultivars were grown to a dry weight of about 0.2 g per plant at four constant temperatures with high light intensity and ample nutrients. Relative growth rates (RGR) were sigmoidally related to temperature, averaging 0.11 g/g/day at 10 °C and 0.35 g/g/day at 22 °C. The cultivars Cobham Green and Avoncrisp had higher RGRs than the others, but the cultivar-temperature interaction was not statistically significant. Temperature affected both components of RGR, i.e. net assimilation rate and leaf area ratio, about equally: the faster-growing cultivars had higher net assimilation rates than the others. Growth rate predictions from the cabinet work agreed fairly well with observations made in the field.

Effects of weed competition for different periods on the growth and yield of red beet

Abstract: SummaryIn four field experiments during 1968–70 annual weeds were removed by hand at different times from crops of red beet drilled at the end of April, and the effects on growth and yield determined. The presence of weeds at densities up to 1300/m2 during the first 4 weeks after 50% crop emergence did not affect yield if the crop was subsequently kept clean, and at low densities this period was extended. When 15–240 weeds/m2 remained throughout, yields of roots were reduced by 45–98%. Once competition began, fewer leaves were formed which were smaller, had a lower chlorophyll content and died more rapidly than those of the weed-free crop, but there was a considerable capacity for recovery after the weeds had been removed. It was only necessary to keep the crop clean for 2–4 weeks after 50% emergence; weeds that emerged after this were effectively suppressed by the crop. There was no ‘critical period’ of weed competition, and a single weeding at an appropriate time was sufficient to give a yield equal to ...

The strength and fracture properties of glass-ceramics

Abstract: The effect of an isothermal heat-treatment on the strength and fracture surface energy of a glass-ceramic derived from a lithium silicate glass has been studied. It is found that the strength and effective surface energy for crack initiation increase as the mean free path in the intercrystalline glass decreases. The strengthening and toughening mechanisms are discussed.

Selection for high self-incompatibility in inbred lines of brussels sprouts

Abstract: An attempt to improve the self-incompatibility of an advanced inbred line of Brussels sprouts by selection has been unsuccessful. The apparent plant-to-plant variation in self-incompatibility has little or no genetic basis. It results from environmental effects and from intrinsic physiological differences between flowers on a single plant. A temperature rise from 17°C to 26°C markedly increases the self-compatibility of the lines tested, but no evidence was found for end-of-season compatibility. The best methods for producing inbreds with high and consistent self-incompatibility are discussed.

Glasshouse evaluation of some systemic fungicides for control of clubroot of brassicae

Abstract: SUMMARY Of nine systemic fungicides screened as soil mixes against clubroot, only the precursors of methyl benzimidazol-2-ylcarbamate (MBC) or ethyl benzimidazol-2-ylcarbamate (EBC) gave promising results. Benomyl was the most effective, usually giving control at 250 mg/kg dry soil. Most fungicides were less effective against an isolate of Plasmodiophora brassicae from Brussels sprouts than against one from rape. Disease control was slightly better on cabbage than on a highly susceptible rape variety.