Petrophysical measurement of ODP Leg 122 and 123 samples (Tables 1, 2)

The capillary-pressure characteristics of 22 samples of lithified post-Paleozoic Indian-Ocean carbonates were compared to published data from older carbonate rocks (lower Paleozoic Hunton Group of Texas and Oklahoma). The Indian-Ocean samples are considerably more porous than are the Paleozoic samples, yet all of the Indian-Ocean samples fit readily into a descriptive petrofacies scheme previously established for the Hunton Group. The Indian-Ocean samples may be assigned to four petrophysical facies (petrofacies) based on the shapes of their capillary-pressure curves, their pore-throat-size distributions, their estimated recovery efficiency values (for nonwetting fluids), and the visual characteristics of their pore systems, as observed with a scanning-electron microscope. Petrofacies assignments for the Indian-Ocean samples are as follows. Petrofacies I includes six samples collected from the coarse basal portions of event deposits (primarily turbidites). These samples have large throats, leptokurtic throat-size distributions, low- to moderate recovery efficiency values, concave cumulative-intrusion capillary-pressure curves, and high porosity values. Petrofacies II includes two sedimentologically dissimilar samples that have medium-size throats, platykurtic throat-size distributions, moderate- to-high recovery efficiency values, gently sloping cumulative-intrusion capillary-pressure curves, and high porosity values. Petrofacies III includes two polymictic sandstones and a skeletal packstone that have small throats, polymodal throat-size distributions, moderate recovery efficiency values, gently sloping cumulative-intrusion capillary-pressure curves, and high porosity values. Petrofacies IV includes 11 samples, mostly recrystallized neritic carbonates, that have small throats, leptokurtic throat-size distributions, high recovery efficiency values, convex cumulative-intrusion capillary-pressure curves, and low porosity values. Comparison of petrofacies assignment to core-, thin-section-, and smear-slide data, and to inferred depositional setting, suggests that pore systems in most samples from Holes 765C and 766A result from primary depositional features, whereas pore systems in samples from Hole 761C and one sample from Hole 765C have been strongly influenced by diagenetic processes. For Hole 761C, prediction of petrophysical parameters should be most successful if based on diagenetic facies patterns. By contrast, the distribution of favorable reservoir facies and of permeability barriers in less highly altered rocks collected from Holes 765C and 766A is related to depositional patterns. Recovery efficiency is inversely related to both porosity and median throat size for the present data set. This relationship is similar to that observed for carbonates of the lower Paleozoic Hunton Group and the Ordovician Ellenburger dolomite, but opposite of that observed for some other ancient carbonates. The coarse deposits of the massive basal units of turbidites are petrophysically distinct and form a coherent petrophysical group (Petrofacies I) with substantial reservoir potential. Two samples assigned to Petrofacies I have extremely large throats (median throat size at least 4 ?m, and at least six times that of any other sample) and therefore high permeability values. These two samples come from thin, coarse turbidites that lack or have poorly developed fine divisions and are interpreted to have been deposited on channeled suprafan lobes in a proximal mid-fan setting. The restriction of extremely high permeability values to a single depositional facies suggests that careful facies mapping of deep-sea fans in a deliberate search for such coarse turbidites could dramatically enhance the success of exploration for aquifers or hydrocarbon reservoirs. Such reservoirs should have substantial vertical heterogeneity. They should have high lateral permeability values but low vertical permeability values, and reservoir sections should include numerous thin units having widely differing petrophysical characteristics.

Geochemistry of sediments and interstitial waters of ODP Sites 128-798 and128-799

Interstitial waters in sediments below 400 (Site 798) and 435 meters below seafloor (Site 799) have chloride concentrations of 516-527 and 501-515 mM, respectively, lower than the 540 mM of the modern-day Japan Sea. The chemical composition of interstitial waters, bulk sediments, clay-size sediment fraction, and carbonate nodules from Oki Ridge (Site 798) and Kita-Yamato Trough (Site 799), Japan Sea, reflect in-situ diagenetic processes superimposed on geochemical signals that may indicate freshening of Miocene local marginal basin waters. Interstitial waters at both sites exhibit changes in chemical composition which coincide with the occurrence of low-porosity and high-bulk density layers composed of dolomite and opal-CT, which impede diffusive communication with the overlying interstitial waters. Based on interstitial water stable isotope evidence and mass-balance calculations of chloride dilution, diagenetic reactions that involve the release of structural bound water from opal-A and/or clay minerals contribute to the observed geochemical signals, but cannot account for all the measured chloride dilution.

(Table T1) Permeabilities and bulk properties of ODP Hole 191-1179C

One of the objectives of drilling at Site 1179 was to search for microbes or biochemical evidence of microbial activity as part of the ongoing exploration of the depth and extent of the deep biosphere. The existence of living microbes has not been confirmed, but the chemistry of pore waters from the site, such as sulfate and ammonium profiles, is consistent with sulfate reduction and nitrification by anaerobic bacteria. However, chemical profiles are affected by the movement of molecules and ions through porous sediments by diffusion and advection. Permeability is thus an important consideration in the interpretation of pore water chemistry profiles. Moreover, diatomaceous sediments have some unique and, as yet, poorly understood physical properties. The purpose of this research is to measure hydraulic conductivity (permeability) in a suite of sediment samples from Ocean Drilling Program Site 1179 by the transient-pulse method. The sample set consists of four diatom ooze samples from Unit I, one radiolarian ooze sample from Unit II, and one pelagic clay sample from Unit III. The permeability of the clay is 1.92 µd, whereas the permeabilities of the overlying radiolarian and diatom oozes range from 289 to 1604 µd. Among these samples, permeability increases with porosity and grain size, in keeping with the results of previous studies.

Correlation between wet bulk density and carbonate content from IODP Hole 321-U1338A, 321-U1338B and 321-U1338C

Sediment cores collected from the Eastern Equatorial Pacific Ocean display a clear positive second-order relationship between wet bulk density (WBD) and carbonate content. This has long interested the paleoceanography community because detailed Gamma Ray Attenuation Porosity Evaluator (GRAPE) measurements, which approximate WBD, might be used to determine records of carbonate content at very high temporal resolution. Although general causes for the relationship are known, they have not been presented and discussed systematically on the basis of first principles. In this study, we measure the mass and carbonate content of 50 sediment samples with known WBD from Site U1338, before and after rinsing with de-ionized water; we also determine the mass related proportion of coarse (> 63 µm) material. Samples exhibit clear relationships between WBD, carbonate content, mass loss upon rinsing, and grain size. We develop a series of mathematical expressions to describe these relationships, and solve them numerically. As noted by previous workers, the second-order relationship between WBD and carbonate content results from the mixing of biogenic carbonate and biogenic silica, which have different grain densities and different porosities. However, at high carbonate content, a wide range in WBD occurs because samples with greater amounts of coarse carbonate have higher porosity. Moreover compaction impacts carbonate particles more than biogenic silica particles. As such, a single two-component equation cannot be used to determine carbonate content accurately across depth intervals where both the porosity and type of carbonate vary. Instead, the WBD-carbonate relationship is described by an infinite series of curves, each which represents mixing of multiple sediment components with different densities and porosities. Dissolved ions also precipitate from pore space during sample drying, which adds mass to the sediment. Without rinsing samples, simple empirical relationships between WBD and carbonate content are further skewed by salt dilution.

Combining Sr and Na additions in hypoeutectic Al-Si foundry alloys

From recent published data, it is still unclear whether combining additions of Na and Sr have synergistic effects or deleterious interactions, This paper clarifies the interactions between these two modifiers and investigates the effects of such interactions on alloy solidification and castability. It was found that combined additions of Sr and Na do not appear to cause improvement of the modification of the eutectic microstructure even after only a short period after addition. Na addition may promote Sr vaporization and/or oxidation kinetically. leading to a quicker loss of both modifiers, which is blamed for the rapid loss of the modification effect during melt holding. Quenching trials during the eutectic arrest indicate that addition of Sr into Na-modified melts does not alter the eutectic solidification behaviour The effect of Na on eutectic solidification dominates, and the eutectic is observed to evolve with a significant dependency on the thermal gradient, Combining Sr and Na additions produced no beneficial effects on porosity and casting defects. (c) 2005 Elsevier B.V. All rights reserved.

Distinct physiological mechanisms underlie altered glycinergic synaptic transmission in the murine mutants spastic, spasmodic, and oscillator

Spastic (spa), spasmodic (spd), and oscillator (ot) mice have naturally occurring glycine receptor ( GlyR) mutations, which manifest as motor deficits and an exaggerated startle response. Using whole-cell recording in hypoglossal motoneurons, we compared the physiological mechanisms by which each mutation alters GlyR function. Mean glycinergic miniature IPSC ( mIPSC) amplitude and frequency were dramatically reduced (> 50%) compared with controls for each mutant. mIPSC decay times were unchanged in spa/spa (4.5 +/- 0.3 vs 4.7 +/- 0.2 ms), reduced in spd/spd (2.7 +/- 0.2 vs 4.7 +/- 0.2 ms), and increased in ot/ot (12.3 +/- 1.2 vs 4.8 +/- 0.2 ms). Thus, in spastic, GlyRs are functionally normal but reduced in number, whereas in spasmodic, GlyR kinetics is faster. The oscillator mutation results in complete absence of alpha 1-containing GlyRs; however, some non-alpha 1-containing GlyRs persist at synapses. Fluctuation analysis of membrane current, induced by glycine application to outside-out patches, showed that mean single-channel conductance was increased in spa/spa (64.2 +/- 4.9 vs 36.1 +/- 1.4 pS), but unchanged in spd/spd (32.4 +/- 2.1 vs 35.3 +/- 2.1 pS). GlyR-mediated whole-cell currents in spa/spa exhibited increased picrotoxin sensitivity (27 vs 71% block for 100 mu M), indicating alpha 1 homomeric GlyR expression. The picrotoxin sensitivity of evoked glycinergic IPSCs and conductance of synaptic GlyRs, as determined by nonstationary variance analysis, were identical for spa/spa and controls. Together, these findings show the three mutations disrupt GlyR-mediated inhibition via different physiological mechanisms, and the spastic mutation results in compensatory alpha 1 homomeric GlyRs at extrasynaptic loci.

Influence of calcium on the microstructure and properties of an Al-7Si-0.3Mg-xFe alloy

The effect of Ca addition on the microstructure, physical characteristics (density/porosity), and mechanical properties (tensile and impact strength) has been investigated in an Al-7Si-0.3Mg-xFe (x = 0.2, 0.4, and 0.7) alloy. The size of Al-Fe intermetallic platelets (beta-Al5FeSi) increased with increasing Fe content. The addition of Ca modified the eutectic microstructure and also reduced the size of intermetallic Fe-platelets, causing improved elongation and impact strengths. A low level of Ca addition (39 ppm) reduced the porosity of the alloys. The tensile strength was decreased marginally with Ca addition. However, Ca addition improved the ductility of the alloy by 18.3, 16.7, and 44 pet and the impact strength by 44, 48, and 15.8 pct for Fe contents of 0.2, 0.4, and 0.7 pct, respectively.

Improving the solubility and dissolution of poorly soluble drugs by salt formation and the consequent effect on mechanical properties

The bioavailability of BCS II compounds may be improved by an enhanced solubility and dissolution rate. Four carboxylic acid drugs were selected, which were flurbiprofen, etodolac, ibuprofen and gemfibrozil. The drugs were chosen because they are weak acids with poor aqueous solubility and should readily form salts. The counterions used for salt formation were: butylamine, pentylamine, hexylamine, octylamine, benzylamine, cyclohexylamine, tert-butylamine, 2-amino-2-methylpropan­2-ol, 2-amino-2-methyl propan-1,3-ol and tromethamine. Solubility was partially controlled by the saturated solution pH with the butylamine counterion increasing the solution pH and solubility and dissolution to the greatest extent. As the chain length increased, solubility was reduced due to the increasing lipophilic nature of the counterion. The benzylamine and cyclohexylamine counterions produced crystalline, stable salts but did not improve solubility and dissolution significantly compared to the parent compound. The substitution of hydroxyl groups to tert-butylamine counterions produced an increase in solubility and dissolution. AMP2 resulted in the most enhanced solubility and dissolution compared to the parent drug but using the tris salt did not further improve solubility due to a very stable crystal lattice structure. The parent drugs were very difficult to compress due to orientation effects and lamination. Compacts were prepared of each parent drug and salt and their modulus of elasticity values were measured using a three-point bend (Young’s modulus, E0) were extrapolated to zero porosity and compared. Compressibility and E0 were improved with the butylamine, tert-butylamine, cyclohexylamine and AMP2 counterions. The most significant improvement in compression and E0 was with the AMP2 salts. Mechanical properties were related to the hydrogen bonding within the crystal lattice structure for the gemfibrozil salt series.

Pore structure and diffusional properties of hardened cement pastes

This study has investigated the inclusion of pulverised fuel ash (PFA) and blast furnace slag (BFS) into hardened cement pastes (HCP) in retarding the ingress of chloride ions and oxygen molecules from the external environment. The influence of environmental factors such as drying and carbonation on the pore structure and diffusional properties of OPC, OPC/30%PFA and OPC/65%BFS hardened pastes was investigated. Specimens were desorbed from a saturated surface dry condition to a near constant weight at 65% relative humidity (RH) while others were simultaneously exposed to a 65% RH atmosphere and a carbon dioxide atmosphere of up to 5% by volume until there were fully carbonated. The presence of the interfacial zone at the cement paste-aggregate interface was critically reviewed and identified. The influence of the interfacial zone on porosity and chloride ingress in assumed periodic composites of glass bead mortars was also studied. The investigations have demonstrated the following: (a) The use of fly ash and slag in blended cement pastes has resulted in a marked reduction in capillary porosity and rate of chloride ingress. (b) The ratio of oxygen to chloride diffusion coefficients increased from values close to 1 in permeable pastes, to values of around 15 in low-permeability blended fly ash and slag pastes. This supports the view that the diffusion of chloride ions is retarded by the surface charge of the hydrated cement gel in low-permeability pastes. (c) Compared with plain OPC pastes, the carbonation of blended fly ash and slag pastes resulted in a marked increase in the coarse capillary porosity and a corresponding increase in the oxygen and chloride diffusion rates.

Diagenesis and aquifer characteristics of the Sherwood Sandstone Group in North Nottinghamshire

The Sherwood Sandstone Group forms an important aquifer in Eastern England, which in North Nottinghamshire comprises the Nottingham Castle and Lenton Sandstone Formations. The aquifer is formed by an alluvial red-bed sequence dominated by medium-coarse grained sandstones which are texturally immature to submature and have only been subjected to shallow burial diagenesis. These sandstones reached the mature stage of the meso diagenetic regime, and four stages are recognized in their diagenetic history depending upon the physical/chemical processes prevailing and the subsequent effect on porosity and permeability. Stage "One" represents changes including dissolution of unstable silicates, clay replacement, red colouration and precipitation of authigenic minerals (quartz, feldspar, illite, l/S, kaolinite, dolomite, ferroan calcite, calcite). The net result of these changes was porosity reduction. Stage "Two" included changes due to mechanical compaction which resulted in minor porosity reduction. Stage "Three" was the main phase of secondary porosity enhancement. Stage "Four" represents changes taking place in the present groundwater where porosity and permeability may have been increased by dissolution and partly reduced by kaolinite precipitation. Porosity measured by water-resaturation and Hg-injection gave average values of 25.63% and 24.85% respectively. The results are comparable and showed marked correlation especially in highly porous/permeable rocks. Porosity measurements from photomicrographs were markedly offset from laboratory results. Horizontal Kw ranged between 1.43 x 10-5 and 1.13 x 10-1 mm/sec, with an average of  1.68 x 10-2 mm/sec. The estimated KHg ranged between 7.29 x 10-6 and 6.99 x 10-2 mm/sec with an average of 1.47 x 10-2 mm/sec. Both results are significantly correlated for highly porous/permeable rocks. The hydraulic properties are highly dependent upon the diagenetic properties (as most of the pores present are of secondary origin) as well as the pore size distribution. The chemistry of these groundwaters indicates that they are under-saturated with respect to dolomite, calcite, K-feldspar, l/S clay, and montmorillonite. The precipitation of kaolinite,and to a lesser extent illite, is favoured in the present groundwater regime.

Assessment of physical and hydrological properties of biological soil crusts using x-ray microtomography and modelling

Biological soil crusts (BSCs) are formed by aggregates of soil particles and communities of microbial organisms and are common in all drylands. The role of BSCs on infiltration remains uncertain due to the lack of data on their role in affecting soil physical properties such as porosity and structure. Quantitative assessment of these properties is primarily hindered by the fragile nature of the crusts. Here we show how the use of a combination of non-destructive imaging X-ray microtomography (XMT) and Lattice Boltzmann method (LBM) enables quantification of key soil physical parameters and the modeling of water flow through BSCs samples from Kalahari Sands, Botswana. We quantify porosity and flow changes as a result of mechanical disturbance of such a fragile cyanobacteria-dominated crust. Results show significant variations in porosity between different types of crusts and how they affect the flow and that disturbance of a cyanobacteria-dominated crust results in the breakdown of larger pore spaces and reduces flow rates through the surface layer. We conclude that the XMT–LBM approach is well suited for study of fragile surface crust samples where physical and hydraulic properties cannot be easily quantified using conventional methods.

Experiments for CFD-modelling of cooling water and Insulation debris two-phase flow phenomena during loss of coolant accidents

The knowledge of insulation debris generation and transport gains in importance regarding reactor safety research for PWR and BWR. The insulation debris released near the break consists of a mixture of very different fibres and particles concerning size, shape, consistence and other properties. Some fraction of the released insulation debris will be transported into the reactor sump where it may affect emergency core cooling. Experiments are performed to blast original samples of mineral wool insulation material by steam under original thermal-hydraulic break conditions of BWR. The gained fragments are used as initial specimen for further experiments at acrylic glass test facilities. The quasi ID-sinking behaviour of the insulation fragments are investigated in a water column by optical high speed video techniques and methods of image processing. Drag properties are derived from the measured sinking velocities of the fibres and observed geometric parameters for an adequate CFD modelling. In the test rig "Ring line-II" the influence of the insulation material on the head loss is investigated for debris loaded strainers. Correlations from the filter bed theory are adapted with experimental results and are used to model the flow resistance depending on particle load, filter bed porosity and parameters of the coolant flow. This concept also enables the simulation of a particular blocked strainer with CFDcodes. During the ongoing work further results of separate effect and integral experiments and the application and validation of the CFD-models for integral test facilities and original containment sump conditions are expected.

Understanding the link between transglutaminase and the induction of fibrosis in cystic fibrosis (CF)

The emerging role of the multifunctional enzyme, Transglutaminase 2 (TG2) in Cystic Fibrosis (CF) has been linked to its increased expression and intracellular transamidating activity. However, a full understanding of the molecular mechanisms involved still remains unclear despite numerous studies that have attempted to delineate this process. These mechanisms include the NFκB and TGFβ1 pathway amongst others. This study reveals for the first time that the development of fibrosis in CF is due to a TG2-driven epithelial to mesenchymal transition (EMT) via a mechanism involving the activation of the pro-fibrotic cytokine TGFβ1. Using a human ΔF508/W1282X CFTR CF mutant bronchial cell (IB3-1), its CFTR corrected “add-back” cell (C38) as well as a primary human bronchial epithelial cell (HBEC), elevated TG2 levels in the CFTR mutant IB3 cell were shown to activate latent TGFβ1 leading to increased levels found in the culture medium. This activation process was blocked by the presence of cell-permeable and impermeable TG2 inhibitors while inhibition of TGFβ1 receptors blocked TG2 expression. This demonstrates the direct link between TG2 and TGFβ1 in CF. The presence of active cell surface TG2 correlated with an increase in the expression of EMT markers, associated with the CF mutant cells, which could be blocked by the presence of TG2 inhibitors. This was mimicked using the “addback” C38 cell and the primary human bronchial epithelial cell, HBEC, where an increase in TG2 expression and activity in the presence of TGFβ1 concurred with a change in cell morphology and an elevation in EMT marker expression. Conversely, a knockdown of TG2 in the CF mutant IB3 cells illustrated that an inhibition of TG2 blocks the increase in EMT marker expression as well as causing an increase in TEER measurement. This together with an increase in the migration profile of the CF mutant IB3 cell against the “add-back” C38 cell suggests that TG2 drives a mesenchymal phenotype in CF. The involvement of TG2 activated TGFβ1 in CF was further demonstrated with an elevation/inhibition of p- SMAD 2 and 3 activation in the presence of TGFβ1/TG2 cell-permeable/impermeable inhibitors respectively. The use of a comparative airway cell model where bronchial epithelial cells were cultured at the air liquid interface (ALI) confirmed the observations in submerged culture depicting the robustness of the model and reiterated the importance of TG2 in CF. Using a CFTR corrector combined with TG2 inhibitors, this study showed that the correction and stabilisation of the ΔF508 CFTR mutation in the mutant cell forged an increase in matured CFTR copies trafficking to the apical surface by circumventing proteosomal degradation. Thus the results presented here suggests that TG2 expression is elevated in the CFTR mutant bronchial cell via a TGFβ1 driven positive feedback cycle whereby activation of latent TGFβ1 by TG2 leads in turn to an elevation in its own expression by TGFβ1. This vicious cycle then drives EMT in CF ultimately leading to lung remodelling and fibrosis. Importantly, TG2 inhibition blocks TGFβ1 activation leading to an inhibition of EMT and further blocks the emerging fibrosis, thus stabilizing and supporting the maturation, trafficking and conductance of CFTR channels at the apical surface.

A pragmatic approach for engineering porous mannitol and mechanistic evaluation of particle performance

The importance of mannitol has increased recently as an emerging diluent for orodispersible dosage forms. The study aims to prepare spray dried mannitol retaining high porosity and mechanical strength for the development of orally disintegrating tablets (ODTs). Aqueous feed of d-mannitol (10% w/v) comprising ammonium bicarbonate, NH4HCO3 (5% w/v) as pore former was spray dried at inlet temperature of 110-170°C. Compacts were prepared at 151MPa and characterized for porosity, hardness and disintegration time. Particle morphology and drying mechanisms were studied using thermal (HSM, DSC and TGA) and polymorphic (XRD) methods. Tablet porosity increased from 0.20±0.002 for pure mannitol to 0.53±0.03 using fabricated porous mannitol. Disintegration time dropped by 50-77% from 135±5.29s for pure mannitol to 75.33±2.52-31.67±1.53s for mannitol 110-170°C. Hardness increased by 150% at 110°C (258.67±28.89N) and 30% at 150°C (152.70±10.58N) compared to pure mannitol tablets (104.17±1.70N). Increasing inlet temperature resulted in reducing tablet hardness due to generation of 'micro-sponge'-like particles exhibiting significant elastic recovery. Impact of mannitol polymorphism on plasticity/elasticity cannot be ruled out as a mixture of α and β polymorphs formed upon spray drying.

The structure and dynamics of saxicolous lichen communities

The saxicolous lichen vegetation on Ordovician slate rock at the mouth of the River Dovey, South Merionethshire, Wales was described in relation to several environmental variables which include aspect, slope angle, light intensity, rock porosity, rock microtopography and rock stability. Each of the measured environmental variables was shown to influence the lichen vegetation. A number of groups of species which were characteristic of certain environments were described. The data from the saxicolous lichen communities were analysed using multivariate analysis. Qualitative and quantitative data were ordinated, the qualitative data being easier to interpret ecologically, and site number (which reflects distance from the sea and altitude), rock porosity and light intensity were shown to be important environmental variables. A classification of the data was also carried out. The results of the ordination and classification were combined together and a model constructed which describes saxicolous lichen vegetation. A method which uses the model as an aid to the design and interpretation of field experiments is described. The model is applied to an experiment which investigates the effect on growth of transplanting four saxicolous lichens to different aspects. Growth was inhibited in Physcia orbicularis and Parmelia conspersa on rock surfaces of northwest aspect compared with growth on rock surfaces of southeast aspect. Growth was inhibited in Parmelia glabratula ssp. fuliginosa on rock surfaces of southeast aspect compared with rock surfaces of northwesr aspect. The growth of Parmelia saxatilis was similar at both southeast and northwesr aspects. Growth inhibition or stimulation in thalli of Physcia orbicularis, Parmelia conspersa and Parmelia glabratula ssp. fuliginosa after transplantation was consistent with the predictions of the model while the results for Parmelia saxatilis were not as expected. There was evidence that the frequency of Parmelia conspersa and Parmelia glabratula at a site is related to an effect of the environment on the growth of the thalli. There was also evidence that the frequency of Physcia orbicularis at a site is related to an effect of the environment on the establishment phase of the thalli and for the competitive exclusion of Parmelia saxatilis thalli from southeast facing rock surfaces. The distribution of lichens in relation to height on nine rock surfaces was investigated. It was suggested that the distribution of the lichens was influenced by microclimatic factors which are related to height on the rock, environmental variables which are associated with the rock substratum (e.g. rock porosity and rock microtopography) and by historical factors. The pattern of one crustose and one foliose lichen on four rock surfaces of different aspect and slope was investigated. On the vertically inclined surface the density of small thalli of Buellia aethalea and Parmelia glabratula ssp fuliginosa was correlated with the microtopography of the surface in transects horizontally across the rock surface but not in transects vertically down the rock surface. there were consitent differences in the scale and intensity of pattern horizontally and vertically and also a decrease in the intensity of pattern vertically as the slope of the rock surface decreased. These results were consistent with the suggestion of a gradient of microclimatic factors up the rock. The differences in the scale and intensity of pattern in different size classes in the population were consistent with the changes in pattern with time which have been shown to occur during succession in sand dune and salt marsh vegetation. The relationship between thallus size and height on a rock surface and between the radial growth rate and location of a thallus on a rock surface were investigated. Thalli of Parmelia glabratula ssp. fuliginosa were larger at the top of the rock surface than at the bottom and the data were consistent with the suggestion that the colonisation of the rock surface began at the top and, in time, spread downwards. The radial growth rate of the thalli could not be related to variation in slope, porosity, microtopography or directly to height on the rock but could be related to the horizontal location of the thalli on the rock. These results were consistent with the suggestion that here is a gradient of microclimatic factors across the rock surface which is also modified by height on the rock surface. The succession of lichen communities was described by relating the vegetation to rock porosity, rock microtopography, species diversity and rock stability. An initial stage dominated by crustose lichens leads to communities dominated by crustose, foliose and fruticose species. In the late stages of the succession on some rock surfaces crustose species again become dominant. The occurrence of the climax state and cyclic vegetation change in lichen communities are discussed. A mthod of estimating the age structure of a lichen population by relating thallus size to growth rate is described. The sources of error in the method are discussed in some detail and several refinements suggested to increase the accuracy of the method. The population dynamics of Parmelia glabratula ssp. fuliginosa was investigated by applying life tables to the age structures of eight different populations. The data were consistent with a period of relatively constant recruitment of thalli into the populations. Mortality in lichen populations was divided into deaths which occur after fragmentation of the thallus and deaths which occur after catastrophic environmental events. THe data suggest that the rate of fragmenting death is dependent on the age of the thallus while the rate of catastrophic death is dependent on the number of thalli established in an age class. A comparison of the numbers of thalli in each age class in the eight populations suggested that population density is controlled firstly, by climate and secondly, by variables related to the local rock surface environment. The rate of fragmenting death is related to the diversity of the community and the influence of diversity together with environmental variables in fluctuating or cyclic changes in population number.