The reponse of lichen growth to transplantation to rock surfaces of different aspect

Thalli of four saxicolous lichens on slate rock fragments were transplanted from rock surafces to horizontal boards and then to south-east-facing and north-west-facing rock surfaces. The radial growth rate of Physcia orbicularis and Parmelia conspersa thalli declined after transplatation to north-west-facing rock surfaces and was unchanged after transplantation to south-east-facing rock surfaces cmpared with growth rates on the boards. The radial growth rate of P. glabratula ssp. fuliginosa thalli declined after transplantation to south-east-facing rock surfaces and was unchanged after transplantation to north-west-facing rock surfaces compared with grwoth rate on the boards. The radial growth rate of P. saxatilis thalli was similar on the horizontal boards, south-east-facing and north-west-facing rock surfaces. These results are dsicussed in relation to the aspect distribution of the four lichens in South Gwynedd, Wales.

The influence of the frequency of wetting and drying on the radial growth of three saxicolous lichens in the field

Three lichen species were wetted with distilled water at different frequencies during August 1973 to July 1974. The radial growth rates of Parmelia glabratula ssp. fuliginosa and Physcia orbicularis thalli declined with increased wetting while the radial growth rate of Parmelia conspersa thalli increased with wetting frequency until ten experimental wettings per month but at fifteen wettings per month fell to a value near to the control. In the summer months, wetting resulted in a decline in the radial growth of P. glabratula ssp fuliginosa compared with the control but had little influence on the growth of P. conspersa and Physcia orbicularis. In the winter months, wetting had no significant influence on the radial growth of Parmelia glabratula ssp. fuliginosa, while the radial growth of P. conspersa increased and Physcia orbicularis declined compared with controls. These results are interpreted physiologically and in relation to the aspect distribution of the three lichens on rock surfaces.

The use of lichen growth rings in lichenometry: some preliminary findings

Certain species of crustose lichens have concentrically zoned margins which probably represent yearly growth rings. These marginal growth rings offer an alternative method of studying annual growth fluctuations, establishing growth rate-size curves, and determining the age of thalli for certain crustose species. Hence, marginal growth rings represent a potentially valuable, unexploited, tool in lichenometry. In a preliminary study, we measured the widths of the successive marginal rings in 25 thalli of Ochrolechia parella (L.) Massal., growing at a maritime site in north Wales. Mean ring widths of all thalli varied from a minimum of 1.02 mm (the outermost ring) to a maximum of 2.06 mm (the third ring from the margin). There is some suggestion that marginal ring width and thallus size are positively correlated; and hence that growth rates increase in larger thalli in this small population. In a further study on recently exposed bedrock adjacent to Breidalon, SE Iceland, we examined the potential for using marginal growth rings to estimate thallus age of a lichen tentatively identified as a Rhizocarpon (possibly R. concentricum (Davies) Beltram.) and thus confirm the timing of surface exposure (c. 50 years). Collectively, these results suggest: 1) the measurement of marginal rings is a possible alternative method of studying the growth of crustose lichens; 2) O. parella may grow differently to other crustose species, exhibiting a rapidly increasing radial growth rate in thalli >40 mm; 3) where lichens with marginal rings grow on recently exposed surfaces (<60 yrs), minimum age estimates can be made using growth rings as an in situ indication of lichen growth rate; 4) it is suggested that this phenomenon could provide a valuable, previously unexploited, in situ lichenometric-dating tool in areas lacking calibration control.

Growth of crustose lichens: a review

Crustose species are the slowest growing of all lichens. Their slow growth and longevity, especially of the yellow-green Rhizocarpon group, has made them important for surface-exposure dating (‘lichenometry’). This review considers various aspects of the growth of crustose lichens revealed by direct measurement including: 1) early growth and development, 2) radial growth rates (RGR, mm yr-1), 3) the growth rate-size curve, and 4) the influence of environmental factors. Many crustose species comprise discrete areolae that contain the algal partner growing on the surface of a non-lichenised fungal hypothallus. Recent data suggest that ‘primary’ areolae may develop from free-living algal cells on the substratum while ‘secondary’ areolae develop from zoospores produced within the thallus. In more extreme environments, the RGR of crustose species may be exceptionally slow but considerably faster rates of growth have been recorded under more favourable conditions. The growth curves of crustose lichens with a marginal hypothallus may differ from the ‘asymptotic’ type of curve recorded in foliose and placodioid species and the latter are characterized by a phase of increasing RGR to a maximum and may be followed by a phase of decreasing growth. The decline in RGR in larger thalli may be attributable to a reduction in the efficiency of translocation of carbohydrate to the thallus margin or to an increased allocation of carbon to support mature ‘reproductive’ areolae. Crustose species have a low RGR accompanied by a low demand for nutrients and an increased allocation of carbon for stress resistance; therefore enabling colonization of more extreme environments.

Studies on biofilm growth of Pseudomonas aeruginosa PAO1

The development of in vitro techniques to model the surface-associated mode of growth is a prerequisite to understanding more fully the physiological changes involved in such a growth strategy. Key factors believed to influence bacterial persistence in chronic infections are those of the biofilm mode of growth and slow growth rate. Methods for controlling Pseudomonas aeruginosa biofilm population growth rates were investigated in this project. This microorganism was incompatible with the in vitro 47mm diameter membrane filter-based biofilm technique developed for the study of Escherichia coli and Staphylococcus epidermidis by Gilbert et al (Appl. Environ. Microbiol. 1989, 55, 1308-1311). Two alternative methods were designed. The first comprised a 25mm diameter cellulose acetate membrane filter supported in an integral holder. This was found to be limited to the study of low microbial population densities with low flow rates. The second, based on a cylindrical cellulose fibre depth filter, permitted rapid flow rates to be studied and allowed growth rate control of biofilm and eluted cells. Model biofilms released cells to the perfusing medium as they grew and divided. The viability of released cells was reduced during, and shortly after, inclusion of ciprofloxacin in the perfusate. Outer membrane profiles of biofilm populations exhibited at least two bands not apparent in planktonic cells grown in batch and chemostat culture, and LPS profiles of biofilm populations showed variation with growth rate. Cell surface hydrophobicity of resuspended biofilm cells varied little with growth rate, whilst it decreased markedly for cells released from the biofilms as growth rate increased. Cells released from the biofilm were more hydrophilic than their sessile counterparts. Differing growth rates, LPS profiles and hydrophobicity are proposed to have a bearing on the release of cells from the adherent population.

The mechanics of creep crack growth in a Magnox alloy

Magnox AL80 has been used for a study of creep crack propagation. A number of variables have been considered such as specimen geometry,notch root radius, material thickness, creep prestrain and stress level.The work has covered the material behaving under two values of the creep exponent, n=3.5 and n=7, according to the stress level. As well as observing initiation times and crack growth rates, scribed grids have been used to examine the near crack tip strain levels and distributions. It was shown that estimations of COD from notch flank opening can give misleading indications of material behaviour and that a more informative method was to monitor displacements in the material surrounding the crack tip. Strong evidence was found for crack advance being displacement controlled, however it was shown that the COD approach should be considered geometry dependant. The summation of ∈xx and ∈yy provided the most successful description of crack advance as it produced a single value that described propagation in all the cases concidered. The strain distributions indicates that σyy was related to distance from a point ahead of the crack tip by the exponent - (l/n+l) and that σxx is proportional to σyy. The constraint stresses arising in the DEN and CN specimens were evaluated. Initiation time was found to be principally affected by the stress level but was modified by the constraints arising from specimen geometry. Crack growth was found not to obey either the empirical K or σpett relationships but was reviewed in context of the observed strain behaviour.

Creep crack growth in cast steam turbine casing steels

The creep rupture properties of cast ½Cr½Mo¼V and 1Cr1Mo¼V alloy steel used in the manufacture of power station steam generating plant. have been investigated. The effects of constraint and geometry on the creep rupture properties are also considered. The validity of various criteria controlling macroscopic creep crack growth in cast CrMoV alloys has been examined. It is found that neither the stress intensity factor nor reference stress correlate satisfactorily the creep crack growth rates at the test temperature of 550°C. Certain minimum displacements must be achieved for crack initiation and propagation. It is found that this displacement as measured by crack opening displacement or crack aspect ratio, is the same in both compact tension and centre-cracked panel geometries, is invariant with crack length and decreases with increasing constraint. The effect of constraint on creep crack growth rate in the two geometries is less conclusive. A new model describing creep crack growth in cast CrMoV alloy steels has been developed. The model is based on the results from a numerical finite element creep analysis of the relaxation and redistribution of stress ahead of an incubating creep crack . It is found that macroscopic creep crack growth in a material undergoing either plane stress or plane strain deformation can be described by a fracture stress which is based on the Von Mises equivalent stress. It has been shown that this model is capable of rationalising all of the experimental crack velocity data from the cast CrMoV alloys. The resultant degree of data correlation is far superior to that obtained when using the stress intensity factor or reference stress. A cumulative damage creep fracture model based upon the results from the numerical analysis has been developed. It is found that the model is capable of predicting the behaviour of propagating creep cracks in cast CrMoV alloys from smooth bar creep rupture data.

The biology of the lichen Rhizocarpon geographicum: symbionts, growth, ecology, and lichenometry

Rhizocarpon geographicum (L.) DC. is one of the most widely distributed species of crustose lichens. This unusual organism comprises yellow-green ‘areolae’ that contain the algal symbiont which develop and grow on the surface of a non-lichenized, fungal ‘hypothallus’ that extends beyond the margin of the areolae to form a marginal ring. This species grows exceptionally slowly with annual radial growth rates (RGR) as low as 0.07 mm yr-1 and its considerable longevity has been exploited by geologists in the development of methods of dating the age of exposure of rock surfaces and glacial moraines (‘lichenometry’). Recent research has established some aspects of the basic biology of this important and interesting organism. This chapter describes the general structure of R. geographicum, how the areolae and hypothallus develop, why the lichen grows so slowly, the growth rate-size curve, and some aspects of the ecology of R. geographicum including whether the lichen can inhibit the growth of its neighbours by chemical means (‘allelopathy’). Finally, the importance of R. geographicum in direct and indirect lichenometry is reviewed.

L-carnosine affects the growth of Saccharomyces cerevisiae in a metabolism-dependent manner

The dipeptide L-carnosine (β-alanyl-L-histidine) has been described as enigmatic: it inhibits growth of cancer cells but delays senescence in cultured human fibroblasts and extends the lifespan of male fruit flies. In an attempt to understand these observations, the effects of L-carnosine on the model eukaryote, Saccharomyces cerevisiae, were examined on account of its unique metabolic properties; S. cerevisiae can respire aerobically, but like some tumor cells, it can also exhibit a metabolism in which aerobic respiration is down regulated. L-Carnosine exhibited both inhibitory and stimulatory effects on yeast cells, dependent upon the carbon source in the growth medium. When yeast cells were not reliant on oxidative phosphorylation for energy generation (e.g. when grown on a fermentable carbon source such as 2% glucose), 10-30 mM L-carnosine slowed growth rates in a dose-dependent manner and increased cell death by up to 17%. In contrast, in media containing a non-fermentable carbon source in which yeast are dependent on aerobic respiration (e.g. 2% glycerol), L-carnosine did not provoke cell death. This latter observation was confirmed in the respiratory yeast, Pichia pastoris. Moreover, when deletion strains in the yeast nutrient-sensing pathway were treated with L-carnosine, the cells showed resistance to its inhibitory effects. These findings suggest that L-carnosine affects cells in a metabolism-dependent manner and provide a rationale for its effects on different cell types. © 2012 Cartwright et al.

Firm growth and barriers to growth among small firms in India

Empirical work on micro and small firms focuses on developed countries, while existing work on developing countries is all too often based on small samples taken from ad hoc questionnaires. The census data we analyze here are fairly representative of small business structure in India. Consistent with findings from prior research on developed countries, size and age have a negative impact on firm growth in the majority of specifications. Enterprises managed by women have lower expected growth rates. Proprietary firms face lower growth on the whole, especially if they are young firms. Exporting has a positive effect on firm growth, especially for young firms and for female-owned firms. Although some small firms are able to convert know-how into commercial success, we find that many others are unable to translate it into superior growth.

The influence of environment on foliose lichen growth and its biological significance

Radial growth and growth in mass of lichens is influenced by climatic and microclimatic factors and also by substratum factors such as rock and bark texture, chemistry, and nutrient enrichment. Seasonal fluctuations in growth, as measured by radial growth rate (RaGR) per month, often correlate best with average or total rainfall, the number of rain days, or rainfall in a specific season. Temperature is also considered to be an important climatic factor in some studies. Interactions between microclimatic factors and especially light intensity, temperature, and moisture are the most important in determining local annual growth rates. The physical and chemical nature of the substratum has a profound influence on the growth of foliose lichens. Hence, the effects of texture, porosity, rate of drying, and the physical changes of the substratum on growth are likely to influence lichen distributions. Bird droppings may influence growth and survival by smothering the thalli, altering the pH, or adding inhibitory and stimulatory compounds. Nitrogen and phosphate availability may also influence growth. Chemical factors may also have an important influence on lichens of maritime rocks, the effect of salinity and calcium ions being of particular importance. Zinc, copper, and mercury may also be important in lichen growth as they have been shown to affect the chlorophyll content of lichen algae. Effects of environmental factors on growth influence the competitive ability of lichens thus influencing their ecology and distribution.

High rate growth of nanocrystalline diamond films using high microwave power and pure nitrogen/methane/hydrogen plasma

In this work, we investigate the impact of minute amounts of pure nitrogen addition into conventional methane/hydrogen mixtures on the growth characteristics of nanocrystalline diamond (NCD) films by microwave plasma assisted chemical vapour deposition (MPCVD), under high power conditions. The NCD films were produced from a gas mixture of 4% CH4/H2 with two different concentrations of N2 additive and microwave power ranging from 3.0 kW to 4.0 kW, while keeping all the other operating parameters constant. The morphology, grain size, microstructure and texture of the resulting NCD films were characterized by using scanning electron microscope (SEM), micro-Raman spectroscopy and X-ray diffraction (XRD) techniques. N2 addition was found to be the main parameter responsible for the formation and for the key change in the growth characteristics of NCD films under the employed conditions. Growth rates ranging from 5.4 μm/h up to 9.6 μm/h were achieved for the NCD films, much higher than those usually reported in the literature. The enhancing factor of nitrogen addition on NCD growth rate was obtained by comparing with the growth rate of large-grained microcrystalline diamond films grown without nitrogen and discussed by comparing with that of single crystal diamond through theoretical work in the literature. This achievement on NCD growth rate makes the technology interesting for industrial applications where fast coating of large substrates is highly desirable.

Firm growth and firm size

This article analyses the growth rates of the complete population of UK-registered firms for the period 2001 to 2005. We estimate Gibrat's law – that growth rates are independent of firm size – by deciles of the firm size distribution. Whether we are able to reject Gibrat's law varies across deciles. We also show how estimates vary according to the measure of firm size, time period and sample selection.

Gravity spun polycaprolactone fibres for soft tissue engineering:interaction with fibroblasts and myoblasts in cell culture

Poly(ε-caprolactone) (PCL) fibres were produced by wet spinning from solutions in acetone under low shear (gravity flow) conditions. As-spun PCL fibres exhibited a mean strength and stiffness of 7.9 MPa and 0.1 GPa, respectively and a rough, porous surface morphology. Cold drawing to an extension of 500% resulted in increases in fibre strength (43 MPa) and stiffness (0.3 GPa) and development of an oriented, fibrillar surface texture. The proliferation rate of Swiss 3T3 mouse fibroblasts and C2C12 mouse myoblasts on as-spun, 500% cold-drawn and gelatin-modified PCL fibres was determined in cell culture to provide a basic measure of the biocompatibility of the fibres. Proliferation of both cell types was consistently higher on gelatin-coated fibres relative to as-spun fibres at time points below 7 days. Fibroblast growth rates on cold-drawn PCL fibres exceeded those on as-spun fibres but myoblast proliferation was similar on both substrates. After 1 day in culture, both cell types had spread and coalesced on the fibres to form a cell layer, which conformed closely to the underlying topography. The high fibre compliance combined with a potential for modifying the fibre surface chemistry with cell adhesion molecules and the surface architecture by cold drawing to enhance proliferation of fibroblasts and myoblasts, recommends further investigation of gravity-spun PCL fibres for 3-D scaffold production in soft tissue engineering. © 2005 Elsevier Ltd. All rights reserved.

Fatigue crack growth behaviour in molten-metal processed SiC particle-reinforced aluminium alloys

Fatigue crack initiation and subsequent short crack growth behaviour of 2014-5wt%SiC aluminium alloy composites has been examined in 4-point bend loading using smooth bar specimens. The growth rates of long fatigue cracks have also been measured at different stress ratios using pre-cracked specimens. The distributions of SiC particles and of coarse constituent particles in the matrix (which arise as a result of the molten-metal processing and relatively slow cooling rate) have been investigated. Preferential crack initiation sites were found to be SiC-matrix interfaces, SiC particles associated with constituent particles and the coarse constituent particles themselves. For microstructurally short cracks the dispersed SiC particles also act as temporary crack arresters. In the long crack growth tests, higher fatigue crack growth rates were obtained than for monolithic alloys. This effect is attributed to the contribution of void formation, due to the decohesion of SiC particles, to the fatigue crack growth process in the composite. Above crack depths of about 200 μm 'short' crack growth rates were in good agreement with the long crack data, showing a Pris exponent, m = 4 in both cases. For the long crack and short crack growth tests little effect of specimen orientation and grain size was observed on fatigue crack growth rates, but, specimen orientation affected the toughness. No effect of stress ratio in the range R = 0.2-0.5 was seen for long crack data in the Paris region.