Showing papers by "University of Aberdeen published in 1990"

Electroceramics: Characterization by Impedance Spectroscopy

Abstract: Electroceramics are advanced materials whose properties and applications depend on the close control of structure, composition, ceramic texture, dopants and dopant (or defect) distribution. Impedance spectroscopy is a powerful technique for unravelling the complexities of such materials, which functions by utilizing the different frequency dependences of the constituent components for their separation. Thus, electrical inhomogeneities in ceramic electrolytes, electrode/electrolyte interfaces, surface layers on glasses, ferroelectricity, positive temperature coefficient of resistance behavior and even ferrimagnetism can all be probed, successfully, using this technique.

Mechanical impedance to root growth: a review of experimental techniques and root growth responses

Abstract: SUMMARY Mechanicalimpedancetorootgrowthisoneofthemostimportant factorsdeterminingroot elongation and proliferation within a soil profile. Penetrometers overestimate resistance to root growth in soil by a factor of between two and eight and, although they remain the most convenient method for predicting root resistance, careful interpretation of results and choice of penetrometer design are essential if improved estimates of soil resistance to root elongation are to be obtained. Resistance to root growth through pressurized cells containing ballotini considerably exceeds the confining pressure applied externally to these cells. Results from this work are reappraised. Existing models of soil penetration by roots and penetrometers are reviewed together with the factors influencing penetration resistance. The interpretation of results from mechanical impedance experiments is examined in some detail and root responses, including possible mechanisms of response, are discussed.

The Ecology of Chitin Degradation

Abstract: Chitin is the (1→4)-β-linked homopolymer of N-acetyl-D-glucosamine (Fig. 1). The individual polymer chains can be thought of as helices, as each sugar unit is inverted with respect to its neighbors. This leads to their stabilization as rigid ribbons by 03—H … 05 and 06—H … 07 hydrogen bonds. The commonest form of chitin is α-chitin. Its unit cell is of two N,N‵-diacetylchitobiose units of two chains in an antiparallel arrangement. Thus, adjacent polymer chains run in opposite directions, held together by 06—H … 06 hydrogen bonds, and the chains are held in sheets by 07 … H—N hydrogen bonds (Minke and Blackwell, 1978). This gives a statistical mixture of CH2OH orientations, equivalent to half oxygens on each residue, each forming inter- and intramolecular hydrogen bonds. This results in two types of amide groups; all are involved in the interchain C=O … H—N bonds, while half of the groups also serve as acceptors for 06—H … O=C intramolecular bonds. This extensive intermolecular hydrogen bonding leads to a very stable structure, the individual polymer chains eventually giving rise to microfibrils if allowed to crystallize (Gooday, 1983). A less common form of chitin is β-chitin, in which the unit cell is of one N,N‵diacetylchitobiose unit, giving a polymer stabilized as a rigid ribbon, as for α-chitin, by 03—H … 05 intramolecular bonds (Gardner and Blackwell, 1975). Chains are then held together in sheets by C=O … H—N hydrogen bonding of the amide groups and by the CH2OH side chains, forming intersheet hydrogen bonds to the carbonyl oxygens on the next chains (06—H … 07). This gives a structure of parallel poly-N-acetylglucosamine chains with no intersheet hydrogen bonds.

Risk and Return on Real Estate: Evidence from Equity Reits

Abstract: We analyze monthly returns on an equally-weighted index of 18 to 23 equity (real property) real estate investment trusts (REITs) that were traded on major stock exchanges over the 1973-87 period. We employ a multifactor Arbitrage Pricing Model using prespecified macroeconomic factors. We also test whether equity REIT returns are related to changes in the discount on closed-end stock funds, which seems plausible given the closed-end nature of REITs. Three factors, and the percentage change in the discount on closed-end stock funds, consistently drive equity REIT returns: unexpected inflation and changes in the risk and term structures of interest rates. The impacts of these variables on equity REIT returns is around 60 percent of the impacts on corporate stock returns generally. As expected, the impacts are greater for more heavily levered REITs than for less levered REITs. Real estate, at least as measured by the return performance of equity REITs, is less risky than stocks generally, but does not offer a superior risk-adjusted return and is not a hedge against unexpected inflation.

Obesity, Weight Loss and Prognosis in Type 2 Diabetes

Abstract: Medical records were reviewed of all 263 Type 2 diabetic patients from the Aberdeen diabetic clinic who were known to have died in 1985 or 1986 Mean age was 65 years (interquartile range 57-75 years) at diagnosis and 72 (66-80) years for men, 75 (72-83) years for women, at death Life expectancy at age 65 was 35% less than published figures for the general population Analysis of survival in 233 patients who lived more than 1 year (189 overweight) using stepwise multiple regression indicated as significant (p less than 005) adverse independent variables: age at diagnosis, presence of clinical ischaemic heart disease at diagnosis, plasma glucose at diagnosis; and as significant favourable variables: oral hypoglycaemic drug therapy, weight loss in the first year, and an interaction between weight loss and BMI for patients with BMI greater than 25 kg m-2 Changes in fashions over the years are likely to have biased these results towards including oral hypoglycaemic therapy and excluding the expected adverse effect of smoking Mean weight loss at 1 year was 26 kg for those with BMI 25-30 kg m-2, 68 kg with BMI greater than 30 kg m-2, following standard dietetic advice For the average patient each 1 kg weight loss was associated with 3-4 months prolonged survival

Physiology of microbial degradation of chitin and chitosan

Abstract: Chitin is produced in enormous quantities in the biosphere, chiefly as the major structural component of most fungi and invertebrates. Its degradation is chiefly by bacteria and fungi, by chitinolysis via chitinases, but also via deacetylation to chitosan, which is hydrolysed by chitosanases. Chitinases and chitosanases have a range of roles in the organisms producing them: autolytic, morphogenetic or nutritional. There are increasing examples of their roles in pathogenesis and symbiosis. A range of chitinase genes have been cloned, and the potential use for genetically manipulated organisms over-producing chitinases is being investigated. Chitinases also have a range of uses in processing chitinous material and producing defined oligosaccharides.

Electroceramics: Characterization by Impedance Spectroscopy

Abstract: Electroceramics are advanced materials whose properties and applications depend on the close control of structure, composition, ceramic texture, dopants and dopant (or defect) distribution. Impedance spectroscopy is a powerful technique for unravelling the complexities of such materials, which functions by utilizing the different frequency dependences of the constituent components for their separation. Thus, electrical inhomogeneities in ceramic electrolytes, electrode/electrolyte interfaces, surface layers on glasses, ferroelectricity, positive temperature coefficient of resistance behavior and even ferrimagnetism can all be probed, successfully, using this technique.

Hardsetting Soils: Behavior, Occurrence, and Management

Abstract: Hardsetting soils are soils that set to a hard, structureless mass during drying and are thereafter difficult or impossible to cultivate until the profile is re wetted. The term hardsetting, originally used when the concept was first defined, will be used here rather than the hyphenated spelling that has sometimes been used. Only in Australia is this form of behavior specifically identified, mapped, and given the name “hardsetting” (Northcote et al., 1975).

A new mechanism of granite emplacement: intrusion in active extensional shear zones

Abstract: ONE of the principal ways in which continental crust grows is by the incorporation, from deeper within the Earth, of large volumes of granitic magma A 'space problem' exists1 as to how these magmas are accommodated in the crust Traditionally two main emplacement mechanisms have been emphasized: 'forceful' intrusion, whereby buoyancy-driven magmas physically push the crust aside, creating granitic diapirs and balloons; and 'passive' emplacement characterized by replacive mechanisms such as cauldron subsidence and stoping Although more recent work2,3 has demonstrated that space for granites may be created within bends and offsets of large transcurrent faults, the simple view of either forceful or passive still fails to account for the intrusive mechanisms of many granites Here we report the discovery of a new igneous intrusion mechanism In the superbly exposed Proterozoic continental crust of South Greenland we have observed that rapakivi granite was intruded as large-scale sheets along ductile extensional shear zones that were active during emplacement In such a process the space problem seems to be simply resolved

Fate of fibrinogen in human arterial intima.

Abstract: Fibrinogen and fibrinogen/fibrin-related antigen (total FRA) was measured in human normal intima and different types of atherosclerotic lesions and mural thrombi. The amount showed marked variation between groups of tissue samples, but within each group there was a significant correlation between levels of total FRA and low density lipoprotein (LDL), suggesting that some common factor must influence their influx or retention. The total FRA were analyzed by gradient sodium dodecyl sulfate polyacrylamide gel electrophoresis and immunoblotting with antisera to whole fibrinogen and fragments D and E, and fibrinopeptide A (FPA). All intimal samples (but not thrombi) contained fragment X, the first product of plasmin digestion of fibrinogen, but fragment Y was present in only half the samples, and no core-fragment E containing FPA was detected in any sample, suggesting that fibrinogenolysis is limited. By contrast, all samples contained fragment E, which was negative for FPA, so presumably derived from fibrin; they also contained fragments D-dimer and DY, which are characteristic degradation products of cross-linked fibrin. There were no differences between samples obtained during reconstructive vascular surgery and samples obtained at autopsy, so the patterns appear to represent the steady state. This implies that within the intima there is continuous formation of cross-linked fibrin and continuous fibrinolysis, both processes generating fragments that may have atherogenic properties.

Nitrification in coniferous forest soils.

Abstract: Net nitrification rates tend to be low or negligible in the forest floor of many coniferous forests of North-East Scotland. The most likely process controls are substrate availability, pH, allelopathy, water potential, nutrient status and temperature. These are discussed in relation to field and laboratory studies of net and potential rates of nitrification. Fungi make up by far the largest part of the nitrifier community in the coniferous forest floor. Very little is known about the distribution and activity of autotrophs in these systems, although it is certain that in vitro evidence suggesting autotrophs cannot nitrify at pH levels characteristic of coniferous forest soils is unrealistic. Because of the metabolic diversity of nitrifying fungi, a variety of organic and inorganic nitrification pathways may exist in coniferous forests. The possible involvement of free radicles in fungal nitrification in coniferous forest soils is also suggested. A complete understanding of nitrification in coniferous forest soils can only result from field characterisation of N flux such as through the use of 15N. This must be combined with ecophysiological characterisation of the organisms involved in order that the complexity of nitrification in coniferous forest soils can be resolved.

The epidemiology of infertility in Aberdeen.

Abstract: OBJECTIVE--To study the prevalence of infertility, both primary and secondary, outcome of pregnancy, occupation, and uptake of medical services in a total population of women from a geographically defined area. DESIGN--A postal questionnaire survey of an age cohort of women who had completed their fertility, and who were randomly selected from the Grampian Health Board9s primary care register. SETTING--Aberdeen city district. SUBJECTS--1024 Women in the age group 46-50, of whom 130 had to be excluded. Of the remaining 894 women, 766 (86%) responded to the questionnaire. MAIN OUTCOME MEASURES--Response to questionnaire on pregnancy history, the length of time taken to become pregnant each time, and whether medical advice had been sought. RESULTS--Among the 766 women contacted, 602 (79%) reported no difficulties in having children, 56 (7%) had chosen not to have children, and the remaining 108 (14%) had experienced infertility, defined as having difficulty in becoming pregnant for more than two years. In total 68 (9%) women had primary infertility, of whom 41 (5%) eventually conceived. Of the 40 (5%) with secondary infertility, 23 (3%) conceived. Overall, 52 (7%) of the population were left with an unresolved problem of infertility. Only 67 (62%) infertile women had made use of hospital services, and a further 8 (7%) had consulted their general practitioners. Among those who conceived there was no difference in the proportion who sought advice compared with those who did not. CONCLUSION--The overall prevalence of infertility was 14%, although half of these women eventually conceived. Primary infertility was more common than secondary infertility. Only 62% of infertile women attended a hospital clinic for treatment of their infertility.

What is meant by a "controlled" ventricular rate in atrial fibrillation?

Abstract: Reduction of a rapid ventricular rate in atrial fibrillation results in a longer diastolic filling period and a higher left ventricular stroke volume but this is offset by reduced contractility and fewer beats per minute; the net effect on cardiac output is uncertain. Sequences of stroke distances were measured by Doppler ultrasound in 60 resting patients with atrial fibrillation to determine the relation between ventricular rate and linear cardiac output. The slope of the cardiac output/ventricular rate relation was positive in all 20 patients with a ventricular rate less than 90 beats per minute and negative in 16 (40%) of 40 patients with a ventricular rate greater than 90 beats per minute. In atrial fibrillation the ventricular rate can be regarded as "controlled" when the cardiac output/ventricular rate slope is positive and "uncontrolled" when the slope is negative--that is when reduction of ventricular rate would lead to increased cardiac output. As so defined, ventricular rate at rest was controlled in every patient when the ventricular rate was less than 90, controlled in 44 (73%) patients when the ventricular rate was 90-140 beats per minute, and uncontrolled in every case when it was greater than 140 beats per minute. Achieving a target ventricular rate of 90 beats per minute in patients with atrial fibrillation at rest would result in control with the least compromise of cardiac output.

Time of occurrence, duration, and ventricular rate of paroxysmal atrial fibrillation: the effect of digoxin.

Abstract: One hundred and thirty nine episodes of atrial fibrillation were identified from Holter recordings in 72 patients with paroxysmal atrial fibrillation. Paroxysms occurred more often by day than by night, suggesting that attacks are more closely associated with sympathetic than with vagal activity. In 41 patients who were not taking digoxin there were 79 episodes, and in 31 patients who were taking digoxin there were 60 episodes. Significantly more of the episodes that lasted for 30 minutes or more occurred in patients taking digoxin (13/17); the relative risk of a prolonged paroxysm associated with taking digoxin was 4.3 (95% confidence intervals 1.6-11.9). The mean (SD) ventricular rate at the onset of the paroxysms was not significantly different in those taking digoxin (140 (25) beats/min) and in those who were not (134 (22) beats/min). In paroxysmal atrial fibrillation, pretreatment with digoxin does not seem to reduce the frequency of paroxysms, or the ventricular rate when paroxysms occur, but it is associated with longer attacks.

Association of Painful and Painless Diabetic Polyneuropathy With Different Patterns of Nerve Fiber Degeneration and Regeneration

Abstract: We evaluated neuropathological abnormalities in sural nerve biopsies from 6 nondiabetic control subjects and 16 age-matched diabetic patients with different syndromes of sensory polyneuropathy (6 with chronic painful neuropathy [CPN], 4 with newly presenting painful neuropathy [NPN], and 6 with painless neuropathy associated with recurrent neurotrophic foot ulcers [RFU]). Although all but one of the evaluated features of myelinated and unmyelinated fiber pathology could be found in every diabetic patient, certain myelinated fiber abnormalities were associated with the clinical characteristics of the neuropathy. Thus, myelinated fiber density was severely reduced, "empty" Schwann tubes (an index of myelinated fiber degeneration) were increased, and early regeneration (bands of Bungner [BB], nonmyelinated axons) was pronounced in the RFU group. Progression from BB to regenerating myelinated fiber cluster (myelination and maturation) was more successful in patients with CPN and NPN than in those with RFU, and the finding of fibers with disproportionately large Schwann cells (cytoplasm and myelin) relative to axon caliber was exclusive to patients with neuropathic pain. We concluded that 1) unequal rates of successful fiber regeneration may underlie the apparent difference in the extent of myelinated fiber loss between painful and painless diabetic polyneuropathy; 2) myelinated and unmyelinated fiber degeneration and regeneration per se are probably not the cause of neuropathic pain in diabetic polyneuropathy, because each occurred in patients with RFU; and 3) axonal atrophy may be involved in neuropathic pain generation.

Luminescence-based nonextractive technique for in situ detection of Escherichia coli in soil.

Abstract: Measurement of light output by luminometry was used to estimate quantitatively the cell concentrations of luminescent strains of Escherichia coli in liquid culture and inoculated into soil. Strains were constructed in which luciferase production was autoinducible or constitutive. In the former, light output per cell varied considerably during growth but was constant in constitutive strains. In liquid culture, the lower detection limit was in the order of 10(2) cells ml-1. Sensitivity was reduced by approximately 1 order of magnitude for cells inoculated into soil, when 2 x 10(2) to 6 x 10(3) cells g of soil-1 could be detected. Light output measurements were obtained within 5 min of sampling, and luminometry therefore potentially offers a rapid and sensitive detection technique for genetically engineered microorganisms.

Comparison of clinical and experimental uveitis.

Abstract: Uveitis is a term which encompasses many clinical syndromes which would appear to be discrete entities. Both clinically and experimentally, the separation of uveitis affecting only the anterior segment from that affecting the posterior segment has a sound pathogenetic basis. However, clear distinctions among the various forms of endogenous posterior uveitis are more difficult to maintain in the light of evidence from experimental models of autoimmune uveitis (EAU). EAU can be induced by a variety of retinal antigens and each antigen has been shown to induce somewhat different forms of EAU, depending on such factors as dose of antigen, species and strains of animal model, and the type(s) of adjuvant used. However, within each model a similar spectrum of uveoretinal responses can be induced by each antigen suggesting that the pathogenetic mechanisms are probably similar also. In addition, if these models are analogous to human disease, then each clinical entity within this apparently heterogeneous group of ...

The 'Jupiter' sinking: effects on children's fears, depression and anxiety.

Abstract: Twenty-five girls who survived the sinking of the cruise ship 'Jupiter' were compared with three other groups of girls--71 controls from a separate school; 46 girls in the same school who had not wanted to go on the cruise; and 13 girls who were in a 'near miss' group in that they wanted to go but did not get places. All completed the Fear Survey Schedule for Children (revised form), the Children's Manifest Anxiety Scale and the Birleson Depression Inventory. Survivors did not become generally more fearful. Rather, they developed significantly greater fears to stimuli related to the traumatic event. The results are discussed in relation to the conditioning theory of the acquisition of phobias. Language: en

Foraging behavior of abyssal grenadier fish: inferences from acoustic tagging and tracking in the North Pacific Ocean

Abstract: Abyssal grenadier fish Coryphaenoides yaquinae were Coryphaenoides armatus and observed arriving at baits deployed within view of a free-fall video vehicle (FVV) camera on the sea floor at two stations in the North Pacific, Sta. F 32°50′N, 124°W, 4400 m deep in the vicinity of the California current and Sta. CNP 31°N, 159°W, a 5900 m deep oligotrophic station. Included within each bait deployment were one or two ingestible acoustic transmitters. A total of 23 fish at Sta. F and 13 fish at Sta. CNP ingested transmitters and were tracked using an acoustic tracking system (ATEX). The number of fish within view of the camera increased to a mean maximum of 4.7 at 60 min at Sta. F and 11.8 by 400 min at Sta. CNP, a paradox in view of presumed lower fish population density at Sta. CNP. Fish that ingested transmitters moved away at radial velocities between 1 and 15 cm s−1, reaching a mean radius of 233 m by 370 min at Sta. F and 622 min at Sta. CNP. Fish appear to be active foragers with no evidence for a “sit and wait” foraging strategy. Grenadiers generally remained near the sea floor as they dispersed. Only one vertical movement to an altitude of ca 25 m was recorded and this comprised less than 0.2% of tracking time. The number of fish present at the bait was found to correspond to the following relationship: N t = α 0 x (1 − c −xf ) t ⩽ β α 0 x c −xt (c βx − 1) t > β where Nt is number of fish present at time t min after bait reaches the sea floor, α0 is initial arrival rate of fish, β is mean fish staying time and x is the bait decay constant. In accordance with optimal foraging theory staying time (β) is longer at Sta. CNP.

Enteric bacteria and osmotic stress: intracellular potassium glutamate as a secondary signal of osmotic stress?

Abstract: Enteric bacteria have evolved an impressive array of mechanisms that allow the cell to grow at widely different external osmotic pressures. These serve two linked functions; firstly, they allow the cell to maintain a relatively constant turgor pressure which is essential for cell growth; and secondly they permit changes in cytoplasmic composition such that the accumulation of intracellular osmolytes required to restore turgor pressure does not impair enzyme function. The primary event in turgor regulation is the controlled accumulation of potassium and its counterion glutamate. At high external osmolarities the cytoplasmic levels of potassium glutamate can impair enzyme function. Rapid growth is therefore dependent upon secondary responses, principally the accumulation of compatible solutes, betaine (N-trimethylglycine), proline and trehalose. The accumulation of these solutes is achieved by the controlled activity of transport systems and enzymes in response to changes in external osmotic pressure. It has been proposed that the accumulation of potassium glutamate during turgor regulation acts as a signal for the activation of these systems [1,2]. This brief review will examine the evidence that control over the balance of cytoplasmic osmolytes is achieved by sensing of the intracellular potassium (and glutamate) concentration.

Effects of ibuprofen on exercise-induced muscle soreness and indices of muscle damage.

Abstract: Thirty-two volunteers participated in a two-period crossover study in which ibuprofen was tested against an identical placebo for its effectiveness in reducing muscle soreness and damage after two bouts of downhill running. Subjective soreness, quadriceps isometric strength and isometric endurance time at 50 percent of maximum strength, serum activities of creatine kinase, lactate dehydrogenase and aspartate transaminase and serum levels of creatinine and urea were recorded at intervals up to 72 hours after exercise. Each downhill run produced muscle soreness, and a decline in muscle strength and 50 percent endurance time, although these parameters were unaffected by ibuprofen treatment. All serum parameters measured increased after both runs, but for the three enzymes this increase was smaller after the second run. Serum creatine kinase and urea levels were higher in the ibuprofen group after both runs. These results indicate that ibuprofen is not an appropriate treatment for delayed onset muscle soreness and damage.