Showing papers by "University of Reading published in 1977"

Factors controlling grain weight in wheat

Abstract: THE physiological factors controlling differences in grain weight between cultivars of wheat are not fully resolved. The experiments described here indicate that final grain weight in two cultivars of wheat is mainly dependent on the rate of accumulation of dry matter, which in turn is governed by the number of endosperm cells formed. Cell number in the endosperm seems to be regulated by the supply of assimilates available to the grain during the first 2 weeks after anthesis.

Inland penetration of sea‐breeze fronts

Abstract: The advance inland of the sea-breeze past Lasham, 45 km from the south coast of England, has been measured over a period of twelve years. In this time 76 sea-breeze fronts passed Lasham, 36 passed Reading and 12 reached Harwell, 85km from the coast. the rate of advance from Lasham to Harwell in calm or light offshore winds was close to 3 ms−1, and the latter station was passed after sunset at a mean time of 2105 GMT. With onshore winds fronts only appear 30 or 40 km inland, and some fronts may be modified by effects due to the east coast. In some cases detailed measurements were made using pilot balloons, an instrumented motor-glider and radar. the fronts were shown to have raised heads about twice the depth of the following flow and within the heads dry patches occur. Variable secondary flows are inferred and comparison with water-tank models shows that several dynamical features in the tank and in the atmosphere are similar. Measurements support the picture of the development of the front during the day as a gravity current, and theoretical rates of advance are deduced. the observed acceleration of the front in the late afternoon is explained in terms of the increased temperature contrast at the front due to the decrease in solar heating of the sea-air. Shortly before sunset, a sea-breeze vortex may be detached from the rest of the flow. In a case study, it is shown that friction at the upper surface is at least five times that at the ground, and heat and humidity budgets are given for the detached vortex.

Soil damage by intensive arable cultivation: temporary or permanent?

Abstract: Intensive arable production normally involves an increasing frequency of cultivation, and hence an increasing probability of soil compaction, particularly if the soil is cultivated when it is wet. The effects on the potential ability of the soil to produce crops is uncertain, because the relations between soil physical conditions and crop growth are poorly understood. To measure damage requires improved techniques for measuring pore size distribution, as well as pore continuity and stability. Most damage takes the form of a reduction in the number of transmission pores (those greater than 0.05 mm, equivalent cylindrical diameter) although storage pores may also be lost in intensively cultivated soils. Where damage is primarily in the surface soil it can usually be repaired by appropriate cultivations. Where compaction of subsurface soil occurs, or blockage of subsurface pores by dispersion of clay from disrupted aggregates, the damage is less easily repaired. Soils differ considerably in their ability to withstand intensive cultivation. The behaviour of soil aggregates on immersion in water provides a useful guide to those likely to suffer more permanent damage, and those where increasingly intensive production can be safely practised.

Updating prediction models by dynamical relaxation: an examination of the technique

Abstract: A dynamical relaxation technique for updating prediction models is analyzed with the help of the linear and nonlinear barotropic primitive equations. It is assumed that a complete four-dimensional time history of some prescribed subset of the meteorological variables is known. The rate of adaptation of the flow variables toward the true state is determined for a linearized f-model, and for mid-latitude and equatorial beta-plane models. The results of the analysis are corroborated by numerical experiments with the nonlinear shallow-water equations.

Temperature dependence of the electrical conductivity and hall coefficient in 2H‐MoS2, MoSe2, WSe2, and MoTe2

Abstract: The electrical conductivity and Hall coefficient perpendicular to the c-axis of hexagonal MoS2, MoSe2, and WSe2 are measured over the temperature ranges 120 to 1170 K and 140 to 820 K, respectively. The derived temperature-dependent carrier densities are described by n ∼ exp (–E/kT) for temperatures less than 800 K indicating (thermal) energy gaps of 0.38 eV in n-type MoS2, 0.27 eV in n-type MoSe2, and 0.19 eV in p-type WSe2. Above room temperature the carrier mobilities are given by μ ∼ T−α, where α ≈ 1.5 in MoS2, MoSe2 and 2.7 in WSe2. The high-temperature (>800 K) thermal activation energies of conduction correspond to energy gaps of 1.27, 0.95, and 1.33 eV in MoS2, MoSe2, and WSe2, respectively. Similar measurements on MoTe2 crystals grown by bromine vapour transport demonstrate the effects of included bromine on the low-temperature conduction processes.

Energy dispersion in a barotropic atmosphere

Abstract: The propagation of energy on the sphere as described by the linear barotropic vorticity equation is studied. For simple flows, the concept of group velocity is examined. Planetary-scale vorticity anomalies exhibit a surprising lack of dispersion in a hemispheric domain. On the sphere, there is more dispersion and a significant cross-equatorial propagation of energy. Planetary-scale vorticity sources tend to produce an orderly downstream train of waves which exhibit a strong tilt (NE-SW for sources in the northern hemisphere) and cross the equator. Zonally elongated sources produce an almost north-south train of waves. For realistic zonal flows with equatorial easterlies, large-scale transients cross the equator, but the long-term forced response in the opposite hemisphere is small. Comparison of the results with observations of atmospheric wave behaviour is made, and some possible implications are presented.

The cell wall composition and distribution of free mycolic acids in named strains of coryneform bacteria and in isolates from various natural sources.

Abstract: The major cell wall amino acids and sugars in 177 strains of coryneform bacteria were determined using a ‘rapid’method. Representatives were examined for free mycolic acids and the oxygen requirements of all strains were determined. Included were named strains, most of which were labelled Arthrobacter, Brevibacterium, Cellulomonas, Corynebacterium or Microbacterium, and a similar number of unnamed isolates from various natural sources. Strains which contained meso-diaminopimelic acid (DAP) were divided into four groups according to their oxygen requirements, the wall sugars and the occurrence and nature of free mycolic acids. Group 1 strains were mainly facultatively anaerobic and contained arabinose and mycolic acids of the Corynebacterium type. They were considered to be members of Corynebacterium sensu stricto and included Cor. diphtheriae and related animal parasites, Microbact. flavum, and Cor. glutamicum and similar species. Group 2 strains were aerobic, contained arabinose and mycolic acids of the ‘rhodochrous’type and were considered members of the ‘rhodochrous’complex. Group 3 strains were aerobic, contained ribose and no mycolic acids. Most were Br. linens strains from cheese but a few, possibly related strains, were from other habitats. Group 4 strains were aerobic and contained neither a pentose sugar nor mycolic acids and were of unknown taxonomic status. Most remaining strains contained lysine or ornithine in the wall and smaller numbers contained L-DAP or diaminobutyric acid; none contained mycolic acids. The chemotaxonomic data are discussed in relation to recent numerical taxonomic studies of coryneform bacteria.

Compressive fracture in undirectional glass-reinforced plastics

Abstract: The shear mode of compressive failure in unidirectional fibre composites is discussed. A mechanism is described in which the shear deformation is restricted to a band of material inclined to the plane normal to the fibre axes. The relationship between the orientation of the failed band of material and the limiting shear deformation in the band is explained in terms of volumetric strains. Tests are described which demonstrate that, in GRP, this type of failure can propagate from a notch and this notch sensitivity is put forward as an explanation for the apparent inadequacy of the theoretical model. The sequence of events in the propagation of compressive failure is studied by examining serial sections of an arrested failure. It is found that fibre fracture at the boundaries and interlaminar failure within the band follow as a result of increasing shear deformation in the band.

Measurement of pore sizes in fine-textured soils: a review of existing techniques

Abstract: Summary Pore size distributions obtained from the relationship between moisture content and suction are not dependable in fine-textured soils because of shrinkage. To overcome this problem, methods such as nitrogen sorption, mercury intrusion porosimetry, non-polar liquid desorption and thin sectioning have been used. In order to pre-dry samples without changes in the pore system, freeze-drying, organic liquid replacement of soil water, and critical point drying techniques have been employed. These methods of soil drying and pore size measurement are described and compared, and the validity of their use in soil studies is examined. The measurement of pore sizes by water desorption is also discussed.

Nitrogen Nutrition of Cowpea ( Vigna unguiculata )

Abstract: Effectively nodulated, pot-grown cowpea plants were irrigated with nutrient solution containing 25 ppm 15N, and the relative contributions to total plant N status of inorganic and nodule-fixed N were determined. Maximum rates of N assimilation occurred during pod-fill, with nodules contributing ten times more nitrogen than the applied source. Symbiotic fixation supplied over 80% of total plant N throughout growth, and contributed significantly to seed N during late pod-fill, when nutrient N assimilation was negligible. Vegetative N content was greatest at mid pod-fill, and mobilization from this 'pool' was equivalent to 44% of total seed N. The implications of these (and previously reported) data are discussed.

Ribosomes, membranes and organelles during meiosis in angiosperms

Abstract: Evidence is presented from both observational and analytical techniques indicating profound changes to take place in the ribosome population during male and female meiosis in some flowering plants. During microsporogenesis these appear to involve the elimination of the major part of the ribosome complement early in the meiotic prophase, and its subsequent restoration by the disintegration in the tetrad cytoplasm of 'nucleoloids', themselves synthesized in the nucleus during late prophase. In female tissue the process is essentially similar except for differences in the restoration of the ribosome population. Immediately before the eradication of the ribosomes in both sexes, a sizeable proportion of the meiocyte cytoplasm is encapsulated by double, or multiple unit membrane profiles. Significantly this cytoplasm remains unaffected by the agents responsible for the degredation of the ribosome population. These events are also reflected in the organelle populations where cycles of dedifferentiation and redifferentiation take place. In view of evidence from other organisms, it is considered unlikely that these cycles are in any way a prerequisite of meiosis, but more a characteristic of cells undergoing major changes of phase, where a cytoplasmic 'clean-up' is required before the next stage of growth may begin.

The Forcing of Ageostrophic Motion According to the Semi-Geostrophic Equations and in an Isentropic Coordinate Model

Abstract: It has been shown previously how a transformation of coordinates applied to the primitive equations with the geostrophic momentum approximation produces the quite simple semi-geostrophic equations. Here the connection with quasi-geostrophic theory and the role of ageostrophic motions are clarified. The cross-frontal circulation equation of Eliassen (1962) is shown to be applicable in a modified form in three dimensions, and a simple “ω equation” in obtained. A similar analytical development is possible in isentropic coordinates. As an example of the diagnostic use of the equations derived, a study of the formation of an upper air front in a numerical model is given.

Photocontrol of stem elongation in light-grown plants of Fuchsia hybrida.

Abstract: Stems of the caulescent long-day plant, Fuchsia hybrida cv Lord Byron, showed 2 types of response to light. In one, internode length was increased by far-red irradiation given at the end of an 8 h photoperiod: the response was no greater with prolonged exposure and was less when the start of far-red was delayed. The effect of far-red was reversible by a subsequent exposure to red light. Internode length was inversely proportional to the Pfr/P ratio established before entry to darkness and there was no evidence for loss of Pfr during a 16 h dark period. The inhibitory effect of Pfr acted at a relatively late stage of internode growth. With the development of successive internodes a second response appeared in which stems lengthened following prolonged daily exposures to red or far-red light, or mixtures of the two, or to brief breaks with red or white light. In these later internodes, a short exposure to far-red near the middle of the night was not reversible by red because red alone promoted elongation at this time. Internode length increased with increase in the daily duration of light and, when light was given throughout an otherwise dark period of 16 h, with increase in illuminance to a saturation value of 200 lx from tungsten lamps. Elongation increased as a linear function of decrease in photostationary state of phytochrome down to Pfr/P≃0.3; however, internodes were shorter in far-red light than in 25% red/red+far-red. It was concluded that stem length is a net response to two modes of phytochrome action. An inductive effect of Pfr inhibits a late stage in internode expansion, and a phytochrome reaction which operates only in light (and may involve pigment cycling) promotes an early stage of internode development. Stem elongation is thus a function both of the daily duration of light and its red/red+far-red content. The outgrowth of axillary buds was controlled by the first type of phytochrome action only.

Plant Husbandry and Management Techniques for Growing Grain Legumes Under Simulated Tropical Conditions in Controlled Environments

Abstract: Practical solutions are described to problems incurred in growing cultivars of cowpea, soyabean, lima bean and pigeon pea under simulated tropical conditions in controlled environments, namely (a) ‘Saxcil’ growth cabinets in which daylength, day and night temperatures, light intensity and quality, relative humidity and CO 2 , concentration are precisely controlled and can be varied over time; (b) compartmentalized glasshouses and adjoining dark compartments where daylength, and day and night temperatures are automatically controlled and night-break illumination can be provided, and (c) heated plastic film houses in which daylength-insensitive tropical legumes can be grown to maturity during the UK summer months since the environment of the wet tropics can be simulated in all respects other than daylength.

Effect of organic constituents and complexed metal ions on aggregate stability of some east anglian soils

Abstract: Summary Paired soils of high and low organic matter content from the East Anglian silts were used to determine the role of different organic constituents and complexed metal ions in relation to aggregate stability. Although leaching with periodate and borate caused some loss of stability for most of the soils, the changes were much less than those due to extraction of the soils with pyrophosphate or acetylacetone which were more effective in removing organic materials complexed with iron and aluminium. Amounts of iron and aluminium extracted were not well correlated with changes in stability. The results indicate that in these soils polysaccharides are less important to aggregate stability than organic matter bonded to the clay particles through association with aluminium or iron.

A comparison of the structures of vapour-deposited and bulk arsenic sulphide glasses

Abstract: Accurate comparative measurements have been made of the X-ray diffraction pattern of a bulk arsenic sulphide glass prepared from the melt and a 250 μm film prepared by vapour deposition of the evaporated bulk. By using Ag Kα radiation, measurements have been made up to Q = 21 A −1 (Q = 4π sin θ/λ) so as to give good spatial resolution. Significant differences are found between bulk and film specimens, and in particular a shoulder is found on the high r side of the first peak in the distribution function for the film. Also, the film is richer in arsenic than the parent bulk. The results are compared in detail with a number of models, all of which involve covalent bonding requirements being fully satisfied, and it is concluded that there are more AsAs bonds in the film than the minimum required by stoichiometry and that a significant fraction ( ≈ 2 3 ) of these are unusually long ( ≈2.6 A compared to the more usual 2.5 A). The most probable explanation is that the vapour contains a significant fraction of As4S4 species (in which the AsAs distances are ≈2.6 A ) and that the film contains a mixture of molecular species which have undergone considerable polymerization. The extent to which this results in a sheet-like structure similar to that proposed for the bulk glass remains unclear.

Observations on spontaneous hand use in the common marmoset ( Callithrix jacchus )

Abstract: Four male and four female marmoset monkeys were observed to make a total of 5,600 “right”, “left”, or “both” hand responses over seven categories of spontaneous behaviour. Significant and consistent hand preferences were shown for the majority of monkeys in two of the categories of behaviour, but not in the other five. The paper considers some of the methodological difficulties involved in recording “handedness” in a species such as the common marmoset.

Stimulus Selection and Behavioral Inhibition

Abstract: One important area of applied psychology is devoted to the development of techniques for eliminating or weakening some responses so that they may be replaced with others. The psychopharmacologist has become involved in the search for drugs that affect response elimination and the neurochemical mechanisms that control inhibition. The term “behavioral inhibition” has been used as a description and as an explanation in psychopharmacology, and some of these uses will be discussed in later sections of this chapter. First, I will discuss some manifestations of behavioral inhibition and consider the possibility that different neurochemical mechanisms may mediate different sorts of inhibition.

Raindrop impact stress and the breakdown of soil crumbs

Abstract: Summary The stress produced by raindrop impact, calculated as the rate of change of momentum divided by area of contact, was found to be only partly satisfactory in studies of breakdown of paper tissue and soil crumbs. The calculated stresses for failure did not agree closely with values found by other methods, and varied systematically with raindrop size. The differences were related to the effect of duration of application of stress, and to the concentration of stress around the periphery of the drop.

The photoelectron spectrum of N2, and partial cross sections as a function of photon energy from 16 to 40 eV

Abstract: The Daresbury electron synchrotron has been used to provide photons from 16 to 40 eV for an investigation of the photoelectron spectrum of molecular nitrogen. A cylindrical mirror analyser was designed so as to obtain partial cross sections which are not dependent upon the asymmetry parameter $\beta $ of the ejected photoelectrons. Partial cross sections are reported for individual vibrational states of the $\text{N}\_{2}^{+}$ ion over the region covered by the Hopfield bands and their associated photoionization continua to 20.5 eV. Allowance has been made in the data for the resonant scattering of electrons from residual N$\_{2}$ through the formation of the short-lived state of N$\_{2}^{-}$ and for the photo dissociation of N$\_{2}^{+}$. Partial cross sections for the electronic states of the N$\_{2}^{+}$ ion are reported which allow recent theoretical predictions to be studied. Reasonable agreement is found between theory and experiment above 30 eV for the X $^{2}\Sigma \_{\text{g}}^{+}$ state of N$\_{2}^{+}$. There is also good agreement between theory and experiment for the B $^{2}\Sigma \_{\text{u}}^{+}$ state except near threshold. The data for the A $^{2}\Pi _{\text{u}}$ state show a steady departure from theory towards the higher photon energies.

An Intersection Theorem for a Collection of Families of Subsets of a Finite Set

Abstract: In this note we prove the following theorem. THEOREM 1. Let k, t #s 1. Let s/ t = {A n , A t2 A lrt } be sets of subsets of {1, ..., m}, where U U r t), A hh * 0 (l < 'i < h < U l < h < r «i (C)' if m/k ^ t, bounds are best possible. If t ^ 2, a/?rf m ^ 2k when t = 2, and r x ^ ... ^ r f and (m\\ there is equality in the bounds then either i\\ = I I, r 2 = ... = r t = 0 if m/k ^ /, or \\ k J (m-\\ \\ r, = ... =r t =y k \\ if m/k I m\\ Of course the bound I 1 corresponds to the case when j / t (say) consists of lm-\\ \\ all ^-subsets of {1, ..., m). To obtain r x +... +r t = t j 1 is also simple: for each \\k~\\ I i, 1 ^ i ^ /, we let J/,-consist of all A>subsets of {1,..., m} which contain the element 1. There is no ambiguity in the statement of the theorem when m/k — t, for the two bounds then have the same value. When / = 1 the theorem is trivially true, so we shall henceforth assume that t ^ 2. The Erdos-Ko-Rado theorem [3] is a consequence of this theorem [take t ^ m/k and let s# x = ... =s/ t ]. First we explain the fundamental structural ideas which give rise to the theorem.

Quantitative data on the carrying of young captive monkeys (Callithrix jacchus) by other members of their family groups

Abstract: Quantitative data are reported on the relative extents to which young common marmosets were carried by other members of their families during the first four weeks of life The paper also includes data on the composition of the Reading colony

Nitrogen Nutrition of Cowpea (Vigna unguiculata). I. Effects of Applied Nitrogen and Symbiotic Nitrogen Fixation on Growth and Seed Yield

Abstract: Effectively nodulated cowpea plants, grown in pots without applied nitrogen, were vegetatively equal to non-nodulated plants supplied with 60 ppm N throughout growth (88 days) and produced significantly greater seed yields. Supplying non-nodulated plants with 120 or 240 ppm N improved seed yields (but not significantly) compared with plants completely dependent on symbiotic fixation. Nodulation promoted branching, and improved pod set and/or retention compared with plants relying on applied N.

On the shapes of passive suspension feeders

Abstract: In situ observations have been made on the shapes of passive suspension feeders in currents. Particular shapes occur in different animal groups and may constitute adaptations to maximise particle capture. Flat fans are found in oscillating and tidal currents and radial or bushy arrangements occur under turbulent conditions. In persistent unidirectional currents dish-shaped fans with the concave side facing the current may be found. In other current regimes small-scale, dish-shaped filters are often found within larger supporting structures. Laboratory tests with models suggest that dish-shaped filters may capture a greater proportion of available particles than flat filters of the same area. In a variety of suspension feeders the food-catching surfaces are located on the leeward side of the supporting structure. It is suggested that the relatively low current velocity, microturbulence and eddying which occurs to leeward probably favours particle capture. When currents change direction mobile animals such as crinoids can actively re-orientate and maintain the leeward location of their food catching surfaces. The shapes of some sessile animals allow passive re-orientation which achieves the same result. These shapes are mounted on flexible stems and include cones, spirals and shallow V-sectioned pinnate fans. These structures are only stable when their apices face upcurrent, food-catching surfaces are located on their leeward sides, within the cones or V-sections.

A Note on the Instability of the African Easterly Jet.

Abstract: A stability analysis has been performed for an easterly lower tropospheric jet which approximates the observed flow over West Africa during summer. The most unstable disturbance has a growth rate of 0.27 day−1, a wavelength close to 4000 km and a phase speed of about 9 m s−1. Although gross features of its energetics are similar to those found by Rennick in a recent theoretical study, there are significant differences in horizontal structure. The present results appear to be in closer agreement with observation.