5,124 research outputs found
Using tree ring cellulose as a tool to estimate past tritium inputs to the ocean
No full textTritium (3H) concentrations in tree rings should reflect ambient precipitation. Thus, to improve knowledge of the 3H input to the oceans, we developed a new technique to measure 3H concentrations in annual tree rings. Measurements of 3H were made on cellulose, the primary constituent of wood, as the isotopic signal of its carbon bound hydrogen atoms should be unchanged since biosynthesis. Traditional cellulose extraction techniques from softwoods are slow and were found to not yield reproducibly pure cellulose. Therefore, a new microwave method was developed which reduces extraction times from 3–5 days to approximately 3 h. Potential 3H contamination from the hydroxyl groups of the cellulose molecule was subsequently removed by exchange with 3H-free NaOH, thus avoiding the dangers of working with large amounts of cellulose nitrate. The validity of the technique was tested by presenting a 3H time series from a cedar tree which grew in Tollymore Forest Park, Northern Ireland, for comparison with 3H data from the Valentia weather station. We find that the 3H in the cellulose clearly reflects the 3H in precipitation with no significant smearing of the bomb signal. A simple box model illustrates that the maximum reservoir residence time of source water for the tree is less than 1 yr, suggesting that groundwater is not a major source of water for this tree. In general, however, the groundwater input needs to be quantified for accurate 3H reconstructions to be made. This work demonstrates the potential of using 3H in wood cellulose as a proxy for 3H in precipitation and, thus, opens the door to reconstruction of past 3H inputs to the ocean
Higher cortisol:cortisone ratios in the preovulatory follicle of completely unstimulated IVF cycles indicate oocytes with increased pregnancy potential
No full textBACKGROUND: Conception following gonadotrophin-stimulated IVF and embryo transfer has been associated with a higher intrafollicular cortisol:cortisone ratio and decreased metabolism of cortisol to cortisone. The role of glucocorticoids in human oocyte maturation is not fully understood, but active glucocorticoid (cortisol) may be important. This study relates intrafollicular cortisol and cortisone concentrations to oocyte fertilization and embryo implantation in unstimulated cycles. METHODS: Patients aged <40 years with favourable sperm underwent unstimulated IVF–embryo transfer. Study 1 related intrafollicular cortisol levels to oocyte and IVF outcome: (i) fertilized, pregnant (n = 9); (ii) fertilized, not pregnant (n = 21); and (iii) unfertilized (n = 12). Study 2 was a case–control study of 27 patients (same outcome groups of equal size) which measured intrafollicular cortisol, cortisone and the cortisol:cortisone ratio. RESULTS: Conception cycles demonstrated higher cortisol concentrations compared with the fertilized group (study 1) [median (95% confidence interval): 299 (249–330) versus 227 nmol/l (185–261); P < 0.05] and higher cortisol:cortisone ratios when compared with the unfertilized group (study 2) [7.38 (5.23–9.19) versus 3.56 (1.75–7.46) respectively; P = 0.02]. Of the women with cortisol:cortisone ratios greater than the outcome independent mean of 5.90, 58% conceived compared with only 13% with ratios <5.90 (P < 0.02). CONCLUSION: Higher cortisol:cortisone ratios in conception cycles suggest that active glucocorticoid may be important for final oocyte maturation and embryo implantation in unstimulated cycles
Past veterinarians in South Africa
Get PDFAn alphabetical list containing short biographies of all deceased South African veterinarians up to 1990.[compiled by] P.J. (Bill) PosthumusVolume 1: AL -- Volume 2: M-ZAlso available in print http://137.215.9.20/record=b1893606ab2013ab201
Open brief aan den WelEdel. Gestr. Heer P.J. Joubert
No full textleyds-70-7201.pdf created from original pamphlet in the WJ Leyds Collection held in the Africana Section of the Stellenbosch University Library and Information Service.Dutch open letter to P.J. Joubert concerning a railroad concession granted to the author and two of his friends in 1885
Design, Modeling and Simulation of a 52MHz MEMS Gyroscope Device in 1.5um SOI
No full textIn this thesis , a simulation model of a MEMS gyroscope is presented. The model enables mode matching and analysis of the dynamic behavior of a gyroscope. Furthermore, the model allows the optimization the design parameters of the gyroscope. The simulated gyroscope operates at a frequency of 52MHz with amplitudes of 10nm and quality factor of 50,000. Finally, the drive mode measurements are presented at different bias voltages.Microelectronics & Computer EngineeringElectrical Engineering, Mathematics and Computer Scienc
Het gemeentelijk Investeringsraadsel: Het verband tussen gemeentelijke investeringen en lokale welvaartsontwikkeling
No full textDit proefschrift gaat over de vraag in hoeverre in Nederland de lokale welvaartsontwikkeling wordt bepaald door de gemeentelijke investeringsinspanning. Op project niveau is meestal wel het een en ander bekend over de maatschappelijke effecten, maar over de impact van de totale investeringsinspanning ontbreekt zowel fundamentele als toepasbare kennis. Het is een raadsel dat nog opgelost dient te worden. De doelstelling van dit proefschrift is daaraan een bijdrage te leveren.Housing System
Coupled thermo–hydro–mechanical processes for the Dutch radioactive waste repository
No full textDisposal of spent nuclear fuel and long lived radioactive waste in deep clay geological formations is one of the promising options worldwide. In this concept of the geological disposal system, the Boom Clay is considered as a potential host rock when designing a generic waste repository in the Netherlands. For design and evaluation of a repository for geologic disposal of nuclear wastes one of its principal concern is the thermal loading. High-level radioactive waste and spent fuel generate considerable amounts of heat. When those waste types are disposed in a geological repository the elevated thermal effect on the behaviour of soils surrounding nuclear waste disposal give rise to change in hydraulic and mechanical properties is a significant factor for repository design. Understanding these time-dependent phenomena processes in relation to both the effects of pore water dissipation and of the thermal expansion is essential for reliably assessing repository performance and evaluating the safety case. This paper presents some of the investigation on the thermal processes with emphasis on the coupled Thermo-Hydro- Mechanical (THM) processes for the disposal concept of a radioactive waste disposal facility, in Boom Clay at a depth of about 500m.Geo-engineerin
Probabilistic performance assessment of a deep tunnel for a radioactive waste repository in French COx claystone
No full textA preliminary probabilistic study of the stability of a circular drift excavated for a radioactive waste repository in the French Callovo-Oxfordian claystone is presented and discussed. An analytical mechanical model assuming isotropic elastic behaviour and linear plastic softening was used. Particular emphasis here is placed on the uncertainty of mechanical property values. The test results from several laboratories showed considerably variable property values and they have been interpreted statistically in this investigation. The obtained statistical results were used in a Monte Carlo framework. The performance of the drift was evaluated in terms of the probability of threshold exceedance in the extent of the plastic zone.Geo-engineerin
Variability in reference point microindentation and recommendations for testing cortical bone: location, thickness and orientation heterogeneity
No full textReference Point Indentation (RPI) has been proposed as a new clinical tool to aid the diagnosis of Osteoporosis. This study has examined the performance of the tool within entire femurs to improve the understanding of the mechanical properties of bone and also to guide future RPI testing to optimize repeatability of results obtained using the technique. Human, bovine, porcine and rat femurs were indented along three longitudinal axes: anterior and posterior: medial and lateral as well as around the circumference of the femoral head and neck. Cortical and subchondral bone thickness was measured using CT and radiography. The study shows that in some samples, bone is too thin to support the high loads applied with the technique and in these cases, RPI values are highly influenced by thickness. The technique will be useful in the mid-shaft region where cortical thickness is greatest, providing previously established guidelines are followed to optimize measurement repeatability, including performing multiple measurements per sample and investigating multiple samples. The study has also provided evidence that RPI values vary significantly with test site, hence mechanical properties should not be inferred from RPI findings alone away from the test site, even within the same bone. In conclusion, RPI appears to be a useful tool for scientific investigation; however further work is required to examine the feasibility of using RPI for assessing differences between healthy and diseased bone in a clinical settin
Achteraf bekeken: Architectuur in Suriname 1951 tot 1969: Bouwwerken ontworpen door ir. P.J. Nagel (1921-1997)
No full textDit boek bestaat hoofdzakelijk uit foto’s van bouwwerken in Suriname, ontworpen door ir. Peter Jacobus Nagel in de periode 1951-1969. Ingenieur P.J. Nagel is afgestudeerd aan de Technische Hogeschool Delft. In dit boek wordt beschreven het leven van Nagel: zijn studietijd, eerste werkkring op Aruba, leven en werken als zelfstandig architect in Suriname van 1951 tot 1963 en tot slot zijn activiteiten in- en vanuit Nederland
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