Showing papers by "University of Hertfordshire published in 1975"

Long-range transport of photochemical ozone in north-western Europe

Abstract: Measurements of the concentrations of ozone and trichlorofluoromethane in the atmosphere over various parts of the southern British Isles provides evidence to suggest that photochemical ozone and the pollutants from which it is formed may be transported into the region from their origins in continental Europe. It seems likely, therefore, that even isolated areas, away from centres of industrialisation, may suffer the effects of this pollution.

Lateral compressibility and penetration into phospholipid monolayers and bilayer membranes

Abstract: THE phospholipid bilayer1 in certain biological membranes is maintained so that the range of temperature over which the gel-to-liquid crystal transition occurs includes the environmental temperature2. As a result, clusters of phospholipid molecules in crystalline and liquid-crystalline states1 coexist in the membrane and the isothermal lateral compressibility of the membrane lipids is enhanced3. Any increase in compressibility should facilitate insertion of foreign molecules into the bilayer thereby affecting transport across the membrane. Indeed, there is evidence that transport of ions4,5 and sugars3, and penetration of an enzyme6 is increased when the chain-melting transition of the lipids occurs. The lateral compressibility of phospholipid bilayers has not been measured, however, and there is no direct evidence for an increase in compressibility at the point where the gel-to-liquid crystal phase transition occurs. In order to measure lateral compressibility, compression solely in the plane of the bilayer is required. Such directed compression of bilayers will be difficult but it can be readily achieved with monolayers at the air–water interface. Since the molecular packing in such monolayers of phospholipids is equivalent to that in bilayers dispersed in excess water1,7, this model system is particularly convenient for exploring the role of lateral compressibility. Here we show (1) how the compressibility of lecithin mono-layers varies with packing density and changes at the chain-melting transition, and (2) how penetration of a hydrophobic protein is dependent on the compressibility.

Turbulent diffusion within a wheat canopy: II. Results and interpretation

Abstract: The coefficient of turbulent diffusion was measured in a 1·25m tall wheat canopy using a uniform release of nitrous oxide, the energy and momentum balance methods, and the humidity profile. The nitrous oxide profile gave the most accurate values, KN in the lower two thirds of the canopy, and a regression of the energy balance estimates, KE, against KN had a slope of 1·17 ± 0·10 with a non-significant intercept of 17cm2s−1. The mean day time profile of KN was exponential, K(z) = K(h) exp(−γ(1-z/h)) with γ = 3·9 when u(h) 1·2m s−1. But analysis of KN for the height interval 0·3 to 0·8m shows the importance of thermal stability, and the results are related to the non-dimensional stability parameter g/T(ΔT/Δz/(u(h)h2) where ΔT/Δz is the temperature gradient and u(h) is the windspeed at crop height, h. The large scatter in the results was attributed to the heterogeneity of the crop. Also the wind profile was frequently S-shaped defying a simple one-dimensional analysis and causing the momentum balance to give nonsensical results. Hence it seems unlikely that one-dimensional analysis of transfer can give values of K allowing an accurate estimate of the source and sink distributions within a dense crop canopy.

The influence of moonlight on catches of insects in light-traps in Africa. III. The effective radius of a mercury-vapour light-trap and the analysis of catches using effective radius

Abstract: Using the inverse square law, estimates can be made of the distances at which illumination from a light-trap is equal to that from background sources. From these distances an index of trap radius can be constructed which can be considered as a measure of trap potential. Between new moon and full moon trap radii vary, depending upon the times of the night at which the trap may be operating, in ratios from about 10:1 to 15:1. A comparable index of light-trap catches can be calculated which allows catches to be examined in relation to changing radius of the trap. Analysis of a series of catches in Uganda and Ghana shows that many species are more abundant than expected in periods of moonlight, particularly at and near full moon, the biggest difference between new moon and full moon being about 10:1 for Marasmia trapezalis (Gn.), whereas the Isoptera, Bostrychidae and Spodoptera triturata (Wlk.) are 3–4 times more frequent at full moon. The ratios between catch at new moon and catch at full moon suggest that the primary determinant of catch is the frequency with which insects cross the boundary of a region of influence whose size is determined by a radius of equal energy. Deductions about the pattern of insect activity through a lunation, and nightly, and the general agreement between curves describing the change in radius of the trap and those of trap catches suggest that changes in catch over a lunation can be explained by changes in the effectiveness of the trap. When corrections are made to allow for such changes, all taxa show some increase in numbers in moonlit periods and in many taxa this increase is substantial. Correction of catches should take account of flight periodicity and this periodicity should, if possible, be confirmed by methods independent of light-traps.

A compact sealed pulsed CO 2 TEA laser

Abstract: A compact sealed pulsed CO 2 TEA laser with an operational life exceeding 106pulses has been developed. It provides single-mode output pulses of 1.0-MW peak power in 50-ns full width at half maximum (FWHM) and total energy 110 mJ in 2 μs. The output beam emerges from an 8.5-mm-diam aperture with a full-angle divergence of 3.5 mrad, which is less than 1.5 times the diffraction limited value. With a different optical resonator system, the corresponding multi-mode output exceeds 1.4 MW in 80 ns with a total energy of 300-500 mJ delivered in 4 μs and with a beam divergence of about 10 mrad. These output levels, corresponding to 15-25 J/l, are obtained for a pulse repetition frequency of 2 Hz and are maintained after initial conditioning, even in lasers tested to 2 \times 10^{6} pulses. Hitherto, prolonged sealed operation was not possible because the glow discharge degraded into arcs. This has been overcome in the present device by the addition of small quantities of carbon monoxide and hydrogen to the basic CO 2 -N 2 -He-laser gas mixture before seal-off.

The activity of some pyrethroids, DDT and lindane in smoke from coils for biting inhibition, knockdown and kill of mosquitoes (Diptera, Culicidae)

Abstract: The action of smoke from smouldering mosquito coils against Aedes aegypti(L.), Anopheles stephensi List. and Culex pipiens fatigans Wied. was studied. Smokes from lindane or DDT coils did not inhibit biting of guinea-pigs by Ae. aegypti or A. stephensi nor did they cause knockdown. The pyrethroids (allethrin, pyrethrins, bioallethrin and S-bioallethrin in that order) were increasingly effective in knocking down and killing C. p. fatigans and Ae. aegypti, and their bite-inhibiting activity on Ae. aegypti and A. stephensi increased in the same sequence. Pyrethrins were inferior to allethrin for knockdown of A. stephensi. Smoke from a bioallethrin coil inhibited Ae. aegypti from probing and taking blood from man. Tests in a cylinder of 0·034 m3 and a room of 25 m3 suggested approximate relative potencies of 1:2:4 for allethrin, bioallethrin and S-bioallethrin, the bite-inhibitory and knockdown actions being closely associated. Use of gauze-ended test cages reduced the range of relative potencies. The discussion suggests that the sequence of effects exerted by smoke on a mosquito entering a room is deterrency, expellency, interference with host finding, bite inhibition, knockdown and, eventually, death.

Studies on the toxicity of zinc sulphate and of cadmium sulphate to stone loach Noemacheilus barbatulus (L.) in hard water

Abstract: The toxicity of zinc sulphate and cadmium sulphate to stone loach Noemacheilus barbatulus was examined in an attempt to explain the distribution of the species in two polluted streams. Stone loach in hard water were more sensitive than rainbow trout to zinc, but much more resistant to cadmium. Their disappearance from the Willow Brook, Northants, in 1971–72 could be accounted for by zinc toxicity. A behavioural change, the loss of the instinct to hide during daylight, occurred in subsequently lethal concentrations of cadmium. The accumulation of cadmium in several tissues was also determined.

COMBINED α- AND β-ADRENOCEPTOR BLOCKING DRUG AH 5158: FURTHER STUDIES ON α-ADRENOCEPTOR BLOCKADE IN ANAESTHETIZED ANIMALS

Abstract: 1. AH 5158, 5-(1-hydroxy-2-((1-methyl-3-phenylpropyl)amino)ethyl)salicylamide, competitively antagonised phenylephrine-induced vasopressor responses in anaesthetized dogs, thus confirming that the drug possesses alpha-adrenoceptor blocking activity. 2. In contrast, AH 5158 was a relatively ineffective antagonist of vasopressor responses to noradrenaline in anesthetized dogs. Thus, at the lowest dose-level tested (1 mg/kg) AH 5158 abolished the increase in pulse width caused by noradrenaline, but otherwise had little or no blocking effect in doses as high as 10 mg/kg. Propranolol (0.1 mg/kg) also abolished the increase in pulse width caused by noradrenaline. With both drugs this effect is thought to be a consequence of blockade of the beta-adrenoceptor-mediated cardia stimulant action of noradrenaline. 3. The interaction between AH 5158 and noradrenaline in spinal dogs, anaesthetized cats and pithed rats was very similar to that seen in anaesthetized dogs. 4. Noradrenaline pressor responses were effectively antagonized by AH 5158 in anaesthetized dogs pretreated with cocaine. The degree of block was similar to that obtained when phenylephrine was the agonist in untreated dogs. 5. These results are consistent with the hypothesis that AH 5158 blocks a cocaine-sensitive inactivation process for noradrenaline in addition to blocking alpha- and beta-adrenoceptors. The resultant increase in the level of circulating noradrenaline would tend to counteract the adrenoceptor blocking action of the drug. 6. The implications of these findings are discussed.

Head Morphology of Second-Stage Juveniles of Some Heteroderidae (Nematoda: Tylenchoidea)

Abstract: Scanning electron microscope observations of heads of second stage juveniles of five of the genera of the Heteroderidae are described and the systematic significance of the different forms discussed. Within the genus Heterodera differences in head morphology generally accord with the recognised sub-divisions of the genus.

Effect of Nitrogen Fertilizer on Photosynthesis and Ribulose 1,5-Diphosphate Carboxylase Activity in Spring Wheat in the Field

Abstract: Wheat was grown in the field with different levels of nitrogenous fertilizer, and the rate of photosynthesis and the activity of ribulose 1,5-diphosphate carboxylase in the flag leaves deter mined. Additional nitrogen increased the dry weight and leaf area of the plants, but did not increase grain yield ; the rate of photosynthesis of the flag leaves was unchanged but the activity of ribulose 1,5-diphosphate carboxylase increased. The significance of these observations to the loss of potential yield of wheat and the relationship between photosynthesis and carboxyl ase activity is considered.

Polyacrylic acid-induced resistance to tobacco mosaic virus in tobacco cv. Xanthi

Abstract: SUMMARY Polyacrylic acid (PA) of molecular weight 1700A, 1700B and 3500 caused resistance to infection with tobacco mosaic virus in tobacco cv. Xanthi-nc, when sprayed on the leaves or watered into the soil. The numbers of lesions produced in the treated plants were between 27 and 97% fewer than in the untreated plants depending on the concentration of PA, its molecular weight and the method of application. Some resistance was caused against potato virus X and potato virus Y but only at concentrations that were harmful to the plants. It appears that PA activates a mechanism responsible for localizing viruses in hypersensitive plants.

Effects of Carbon Dioxide on Metabolism by the Glycollate Pathway in Leaves

Abstract: When solutions of [14C]glycollate, glycine, serine, glycerate, or glucose were supplied to segments of wheat leaves through their cut bases in the light, most of the 14C was incorporated into sucrose in air but in C02-free air less sucrose was made. The synthesis of sucrose was decreased because metabolism of serine was partly blocked. Sucrose synthesis from glucose and glycerate in C02-free air was decreased but to a smaller extent ; relatively more CO2 was evolved and serine accumulated. The effects of DCMU and light of different wavelengths on metabolism by leaves of L-[U-14C]serine confirmed that simultaneous photosynthetic assimilation of carbon was necessary for the conversion of serine to sucrose. Of various products of photosynthesis fed exogenously to the leaves a-keto acids were the most effective in promoting photosynthesis of sucrose and release of 14C02 from 14C-labelled serine. This suggests that in C02-free air the metabolism of serine may be limited by a shortage of a-keto acid acceptors for the amino group. In C02-free air added glucose stimulated production of CO2 and sucrose from d-[U-14C] glycerate and no competitive effects were evident even though glucose is converted rapidly to sucrose under these conditions. In addition to a supply of keto acid, photosynthesis may also provide substrates that can be degraded and provide energy in the cytoplasm for the conversion of glycerate to sugar and phosphates and sucrose.

Insect pollination of sugar-beet (beta-vulgaris) seed crops

Abstract: SUMMARY The flowers of sugar-beet crops grown to produce hybrid seed were visited by many species of insects which often carried much sugar-beet pollen on their bodies and could have contributed to pollination.

The Control of Water and Carbon Dioxide Flux in Water-stressed Sugar Beet

Abstract: Changes in leaf and canopy water potential of sugar beet growing in soil of decreasing water content depended on soil water potential and were independent of water flux from the plant when this was varied by changing the water vapour content of the air. The calculated hydraulic conductance of the plant increased as flux increased and decreased as leaf water potential decreased and as the plant aged. The conductances to water vapour of individual leaves and of the canopy decreased as leaf water potential decreased and increased with increasing humidity of the air. The latter effect was independent of changes in leaf water potential. The conductances were not affected by the rate of evaporation or leaf temperature. The rate of photosynthesis was directly related to leaf conductance except in severely stressed, mature leaves in which leaf water potential had a more direct effect on photosynthesis. Stomatal conductances, transpiration, and photosynthesis were greater in young leaves than mature leaves on the same plant and at the same leaf water potential. These results are discussed in relation to current agricultural irrigation practices used for sugar beet.

Transmission of broad bean stain virus and Echtes Ackerbohnenmosaik‐Virus to field beans (Viciajaba) by weevils

Abstract: SUMMARY Sitona lineatus and Apion vorax were the two most common species of weevil on field beans (Vicia faba minor) at Rothamsted between 1970 and 1974. In glasshouse tests, A. vorax was a much more efficient vector than 5. lineatus of broad bean stain virus (BBSV) and Echtes Ackerbohnenmosaik-Virus (EAMV), and both species transmitted EAMV more often than BBSV. Five other species of Apion transmitted the viruses infrequently or not at all. S. lineatus adults transmitted no more often after 8–16 days on infected plants than after 1–2 days. Some A. vorax adults transmitted EAMV, but not BBSV, after feeding on infected leaves for a few minutes. After 4 days on infected plants, A. vorax sometimes remained infective for the following 8 days. No A. vorax collected from woodland plants in spring was infective with BBSV or EAMV, but 4% from bean crops containing seed-borne infection carried BBSV and 17% carried EAMV. BBSV and EAMV were recovered from triturated weevils, but not from weevil haemolymph. Possibly the viruses are transmitted as contaminants of the mouthparts or by regurgitation during feeding, but A. vorax was observed to regurgitate only when anaesthetized. BBSV and EAMV were not transmitted by aphids (Aphis fabae and Acyrthosiphon pisum), nor by pollen beetles {Meligethes spp.). Field observations suggest that infected seed is the main source of BBSV and EAMV in spring-sown crops, and that crops grown from virus-free seed, and isolated from infected crops by 250–500 m, remain free of infection for most of the season.

A comparison of different criteria for selecting binary tests in diagnostic keys

Abstract: SUMMARY The problem of selecting tests to be used in nonprobabilistic binary diagnostic keys is discussed. Five selection criteria are compared and it is shown that all except a new criterion suffer from some deficiency. This criterion cannot be extended easily to cope with multiresponse tests but another criterion, which behaves satisfactorily with binary tests, can be extended in some circumstances. The only criterion which can always be used with multiresponse tests is least satisfactory for binary tests. Consider n populations characterized by p binary characters. An individual sample from one of the populations may be assigned to its population of origin, or identified, by observing the values of its characters. In the following this process of observation will be termed testing and, unless otherwise stated, each test will be assumed to have two possible responses, termed positive and negative. A binary diagnostic key is a device for identifying samples, by applying the tests sequentially in a hierarchical manner. A sequence of test responses leading to an identification is termed a branch of the key. In general, branches will differ in length and the tests they use, although the same test can occur on several branches. Voss (1952) gives an interesting review of the historical development of keys. To construct a key one requires a table giving the responses to thep tests for every population. There are four possible entries in this table: the response may be known to be positive for the whole population, or to be negative, or to be variable within the population, or the response may be unknown, there being no information available about the population value of the character concerned. Clearly, in the latter case, samples from the population may give either positive responses or negative responses and different samples need not give the same response. The first two types of response enable populations to be separated with certainty and when sufficient of these so-called fixed responses occur, all n populations can be identified uniquely. Even when there are insufficient fixed responses to give complete separation of the populations, one may identify a sample to within a group of populations with certainty. Such groups may be further separated, either by using a probabilistic key (Good, 1970) or better by discriminant methods. In this paper we are concerned solely with certain identification and therefore regard variable and unknown responses as equally uninformative, referring to both as unknown responses. An optimum key may be defined as that with minimum average number of tests for identification. Alternative formulations include keys with minimum cost per identification or minimum number of different tests used (Gower & Barnett, 1971; Willcox & Lapage,

Turbulent diffusion within a wheat canopy: I. Measurement using nitrous oxide

Abstract: A new method is described for measuring the vertical component of the coefficient of turbulent diffusion, K, within a wheat canopy. A uniform controlled flux of nitrous oxide was released from a network of nylon tubes at ground level, and K was calculated from the concentration gradient measured at the centre of the network. The method was first used above the canopy when the crop was short, and the results agreed with those obtained from the wind profile and energy balance. Experiments with different sizes of distribution area showed that in most conditions a radius of only 12m was adequate to give a vertical flux that was constant within 15% to a height of 1m in a canopy 1·25m tall. The possible error in K was estimated to be 10 to 15% in the lower half of the canopy increasing to 30 to 40% above 1·0m. This is a useful complement to the energy and momentum balance methods that are very inaccurate in the lower half of the canopy.

Factors Influencing the Strength of Rubbers

Abstract: The strength behavior of rubbers is discussed in terms of fracture mechanics which treats fatigue and tensile failure as crack growth processes from small flaws. Crack growth can be influe...