434 research outputs found
Spatio-temporal patterns in the postglacial flooding of the Great Barrier Reef shelf, Australia
The shelf of the Great Barrier Reef (GBR) was progressively marine flooded from the last glaciation maximum (LGM) (ca 20 ka BP) until the last sea-level highstand (ca 6 ka BP), affecting the depositional evolution of the GBR margin and associated deposits. However, the physiographic variables related to this process have not been fully characterized, especially in relation to the sedimentary processes at the shelf margin. For this study, we used a bathymetric model of the entire shelf and a shelf margin sub-set, divided into 33 latitudinal zones. Postglacial marine flooding was simulated and flooded area (km2), flooding magnitude (km2 per sea-level increment), flooding rate (km2. kyâ1) and coastline length (km) were estimated for each zone, from 130 m to 0 m below present sea level, representing the period from 20 ka to 6 ka BP. Our results show that the postglacial marine flooding did not occur uniformly and that some sub-regions (e.g. the southern-central GBR) had early and rapid flooding. Coastal complexity increased in the mid-postglacial, reaching maximum values at around 9 ka BP. This reflects a coastal landscape evolving from a linear, laterally connected coast to a complex coast dominated by estuaries and lagoons, partly returning to its initial linearity during highstand. Flooding trends and geological evidence make two depositional relationships apparent. Firstly, the timing and magnitude of the off-shelf sediment flux appears linked to the presence and orientation of a shelf-edge rim, and to the extension and morphology of the evolving drainage network. Secondly, the periods of shelf-edge reef development and demise seem to respond to the remobilisation, trapping or redirection of fine sediments. We propose a sedimentation model for the shelf margin and the slope driven by the interplay of sea-level rise and shelf physiography, and we highlight two fundamental processes: (1) the cross-shelf sediment transport related to coastline retreat under rising sea levels, and (2) the effectiveness of transient embayments in redirecting or trapping sediments. The quantifications provided in this study have implications in the estimation of Pleistocene carbonate budgets and the atmospheric carbon cycle, as well as for past human migrations
Leadership in the British civil service: an interpretation
This article is essentially a polemic. The argument is that when politicians and officials now talk of âleadershipâ in the British civil service they do not use that word in the way in which it was previously used. In the past leading civil servants, acting in partnership with ministers and within constitutional constraints, exercised leadership in the sense of setting example, inspiring confidence and encouraging loyalty. The loosening of traditional constitutional patterns, the marginalization of senior officials in the policy process and the emergence of business methods as the preferred model for public Âadministration have led to a political and administrative environment in which leadership in the British civil service is now about encouraging patterns of behaviour which fit in with these changes. Leadership skills are now about âdeliveryâ; they are not about motivation. It is time for politicians, officials and scholars to be open about this
Omentum is highly effective in the management of complex cardiothoracic surgical problems
AbstractObjectives: Vascularized, pedicled tissue flaps are often used for cardiothoracic surgical problems complicated by factors that adversely affect healing, such as previous irradiation, established infection, or steroid use. We reviewed our experience with use of the omentum in these situations to provide a yardstick against which results with other vascularized flaps (specifically muscle flaps) could be compared. Methods: A retrospective review was undertaken of 85 consecutive patients in whom omentum was used in the chest. In 47 patients (group I), use of omentum was prophylactic to aid in the healing of closures or anastomoses considered to be at high risk for failure. In 32 patients (group II), omentum was used in the treatment of problems complicated by established infection. In 6 patients (group III), omentum was used for coverage of prosthetic chest wall replacements after extensive chest wall resection. Results: Overall, omental transposition was successful in its prophylactic or therapeutic purpose in 88% of these difficult cases (75/85). Success with omentum was achieved for 89% of patients (42/47) in group I, 91% of patients (29/32) in group II, and 67% of patients (4/6) in group III. Three patients (3.5%) had complications of omental mobilization. Four patients (4.7%) died after the operation as a result of failure of the omentum to manage the problem for which it was used. Conclusions: Results with omental transposition compare favorably with published series of similarly challenging cases managed with muscle transposition. Complications of omental mobilization are rare. We believe that its unique properties render the omentum an excellent choice of vascularized pedicle in the management of the most complex cardiothoracic surgical problems.J Thorac Cardiovasc Surg 2003;125:526-3
A dedicated electric oven for characterization of thermoresistive polymer nanocomposites
AbstractThe construction, characterization and control of an electric oven dedicated to the study of thermoresistive polymer nanocomposites is presented. The oven is designed with a heating plate capable of reaching 300°C with a resolution of 0.3°C and an area of uniform temperature of 3.8cmĂ2.5cm. The temperature is regulated by means of a discrete proportionalâintegralâderivative controller. A heat transfer model comprising three coupled non-linear differential equations is proposed to predict the thermal profiles of the oven during heating and cooling, which are experimentally verified. The oven is used for thermoresistive characterization of polymer nanocomposites manufactured from a polysulfone polymer and multiwall carbon nanotubes
Phonon and Elastic Instabilities in MoC and MoN
We present several results related to the instability of MoC and MoN in the
B1 (sodium chloride) structure. These compounds were proposed as potential
superconductors with moderately high transition temperatures. We show that the
elastic instability in B1-structure MoN, demonstrated several years ago,
persists at elevated pressures, thus offering little hope of stabilizing this
material without chemical doping. For MoC, another material for which
stoichiometric fabrication in the B1-structure has not proven possible, we find
that all of the cubic elastic constants are positive, indicating elastic
stability. Instead, we find X-point phonon instabilities in MoC (and in MoN as
well), further illustrating the rich behavior of carbo-nitride materials. We
also present additional electronic structure results for several transition
metal (Zr, Nb and Mo) carbo-nitride systems and discuss systematic trends in
the properties of these materials. Deviations from strict electron counting
dependencies are apparent.Comment: 5 pages and 4 trailing figures. Submitted to PR
OH detection by absorption of frequency-doubled diode laser radiation at 308nm
Radiation at 308 nm has been obtained by frequency doubling the output of a commercial diode laser cooled to 165 K. A single pass through a crystal of LiIO3 converted 1 mW of 616 nm radiation to 50 pW of UV, and this was used to detect the OH radical in absorption in a flow tube. Possible extensions of the method for detection of OH in the atmosphere are discussed
Characteristics associated with quality of life among people with drug-resistant epilepsy
Quality of Life (QoL) is the preferred outcome in non-pharmacological trials, but there is little UK population evidence of QoL in epilepsy. In advance of evaluating an epilepsy self-management course we aimed to describe, among UK participants, what clinical and psycho-social characteristics are associated with QoL. We recruited 404 adults attending specialist clinics, with at least two seizures in the prior year and measured their self-reported seizure frequency, co-morbidity, psychological distress, social characteristics, including self-mastery and stigma, and epilepsy-specific QoL (QOLIE-31-P). Mean age was 42 years, 54% were female, and 75% white. Median time since diagnosis was 18 years, and 69% experienced â„10 seizures in the prior year. Nearly half (46%) reported additional medical or psychiatric conditions, 54% reported current anxiety and 28% reported current depression symptoms at borderline or case level, with 63% reporting felt stigma. While a maximum QOLIE-31-P score is 100, participantsâ mean score was 66, with a wide range (25â99). In order of large to small magnitude: depression, low self-mastery, anxiety, felt stigma, a history of medical and psychiatric comorbidity, low self-reported medication adherence, and greater seizure frequency were associated with low QOLIE-31-P scores. Despite specialist care, UK people with epilepsy and persistent seizures experience low QoL. If QoL is the main outcome in epilepsy trials, developing and evaluating ways to reduce psychological and social disadvantage are likely to be of primary importance. Educational courses may not change QoL, but be one component supporting self-management for people with long-term conditions, like epilepsy
- âŠ