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Surface constraints on the depth of the Atlantic meridional overturning circulation: Southern Ocean versus North Atlantic
Paleoclimate proxy evidence suggests that the Atlantic meridional overturning circulation (AMOC) was about 1000 m shallower at the Last Glacial Maximum (LGM) compared to the present. Yet it remains unresolved what caused this glacial shoaling of the AMOC, and many climate models instead simulate a deeper AMOC under LGM forcing. While some studies suggest that Southern Ocean surface buoyancy forcing controls the AMOC depth, others have suggested alternatively that North Atlantic surface forcing or interior diabatic mixing plays the dominant role. To investigate the key processes that set the AMOC depth, here we carry out a number of MITgcm ocean-only simulations with surface forcing fields specified from the simulation results of three coupled climate models that span much of the range of glacial AMOC depth changes in phase 3 of the Paleoclimate Model Intercomparison Project (PMIP3). We find that the MITgcm simulations successfully reproduce the changes in AMOC depth between glacial and modern conditions simulated in these three PMIP3 models. By varying the restoring time scale in the surface forcing, we show that the AMOC depth is more strongly constrained by the surface density field than the surface buoyancy flux field. Based on these results, we propose a mechanism by which the surface density fields in the high latitudes of both hemispheres are connected to the AMOC depth. We illustrate the mechanism using MITgcm simulations with idealized surface forcing perturbations as well as an idealized conceptual geometric model. These results suggest that the AMOC depth is largely determined by the surface density fields in both the North Atlantic and the Southern Ocean
Wear of composite ceramics in mixed-material combinations in total hip replacement under adverse edge loading conditions
Further development of ceramic materials for total hip replacement aim to increase fracture toughness and further reduce the incidence of bearing fracture. Edge loading due to translational mal positioning (microseparation) has replicated stripe wear, wear rates, and bimodal wear debris observed on retrievals. This method has replicated the fracture of early zirconia ceramic-on-ceramic bearings. This has shown the necessity of introducing microseparation conditions to the gait cycle when assessing the tribological performance of new hip replacement bearings. Two novel ceramic matrix composite materials, zirconia-toughened alumina (ZTA) and alumina-toughened zirconia (ATZ), were developed by Mathys Orthop€adie GmbH. In this study, ATZon- ATZ and ZTA-on-ZTA bearing combinations were tested and compared with alumina-on-alumina (Al2O3-on-Al2O3) bearings under adverse microseparation and edge loading conditions using the Leeds II physiological anatomical hip joint simulator. The wear rate (695% confidence limit) of ZTA-on-ZTA was 0.1460.10 mm3/million cycles and that of ATZ-on-ATZ was 0.0660.004 mm3/million cycles compared with a wear rate of 0.7461.73 mm3/million cycles for Al2O3- on-Al2O3 bearings. Stripe wear was evident on all bearing combinations; however, the stripe formed on the ATZ and ZTA femoral heads was thinner and shallower that that formed on the Al2O3 heads. Posttest phase composition measurements for both ATZ and ZTA materials showed no significant change in the monoclinic zirconia content. ATZon- ATZ and ZTA-on-ZTA showed superior wear resistance properties when compared with Al2O3-on-Al2O3 under adverse edge loading conditions. VC 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 00B: 000–000, 2013
Report of the National Science Foundation-Sponsored GeoEngineering Extreme Events Reconnaissance (GEER) Team
The L’Aquila earthquake occurred on April 6 2009 at 03:32:39 local time. The
earthquake was located in the central Italy region of Abruzzo. Much of the damage
occurred in the capital city of L’Aquila, a city of approximate population 73000,
although many small villages in the surrounding regions were significantly damaged
including Paganica, Castelnuovo, and Onna. Collapsed and damaged structures in
L’Aquila included both older masonry buildings and relatively modern reinforced
concrete structures. At the time of this writing, 307 people are known to have died from the earthquake, most in collapsed structures, making this the deadliest earthquake to strike Italy since the 1980 Irpinia earthquake.
A number of reconnaissance teams were mobilized to the affected region in the
weeks following the earthquake. The national institute of geophysics and volcanology
(Istituto Nazionale di Geofisica e Vulcanologia, INGV) mobilized a team of geologists (EMERGEO Working Group) to look for evidence of surface rupture and other effects;
some of their findings are discussed in this report. The GEER team was assembled to
investigate geological, seismological, and geotechnical engineering aspects of the
event. The international GEER team is comprised of members from Italy, Austria,
Switzerland, Greece, and the United states. Team members were selected to provide
needed expertise in geology, engineering geology, GIS applications, earthquake
ground motions, and geotechnical earthquake engineering. The team includes
individuals highly experienced in post-earthquake reconnaissance and relatively young
professionals investigating their first earthquake.
The GEER team did not focus on structural engineering or lifeline aspects of the
event, which were investigated by an EERI team. The GEER and EERI activities were
closely coordinated to optimize resources in the documentation of the valuable,
perishable data associated with the earthquake effects.
The GEER team employed a number of innovative technologies to facilitate
effective reconnaissance. All teams mobilized for field work had a common GPS unit and laptop with a Google Earth (GE) GIS database activity maintained over the course
of the work. The GE database was used to keep track of visited locations, but also
contained maps of surface geology, locations of aftershocks, strong motion stations,
and other information relevant to investigators in the field. Another valuable use of
technology involved LIDAR mapping of a site having significant incidents of ground
failure (Lake Sinizzo).
This report presents the GEER findings. Following this introduction, Chapter 2
describes the geologic and tectonic setting, moment tensor solutions for the mainshock
and several triggered events, analysis of aftershock patterns, and analysis of GPS and
InSAR data. Included in Chapter 2 is a preliminary model of the ruptured fault. Chapter 3 describes the ground motions recorded during the mainshock by a digital instrument array. Metadata associated with the recordings is presented, trends in the recorded ground motions are presented, and preliminary comparisons to ground motion
prediction equations are made. Chapter 4 presents damage patterns, both within
L’Aquila and through comparisons of damage intensities in adjacent villages with similar
construction. The results provide valuable insights into possible site effects on ground
motion in regions where recordings are not available. Chapter 5 presents our findings
on ground failure, defined as permanent ground deformations induced by the
earthquake. Observed ground failure included several rockfalls, seismic compression of
fill materials, and apparent strength loss of soil materials leading to inward movement of the banks of a lake. Chapter 6 reviews the performance of earth dams and earth
retaining structures, both of which generally performed well
Regenerative function of immune system: Modulation of muscle stem cells
Ageing is characterised by progressive deterioration of physiological systems and the loss of skeletal muscle mass is one of the most recognisable, leading to muscle weakness and mobility impairments. This review highlights interactions between the immune system and skeletal muscle stem cells (widely termed satellite cells or myoblasts) to influence satellite cell behaviour during muscle regeneration after injury, and outlines deficits associated with ageing. Resident neutrophils and macrophages in skeletal muscle become activated when muscle fibres are damaged via stimuli (e.g. contusions, strains, avulsions, hyperextensions, ruptures) and release high concentrations of cytokines, chemokines and growth factors into the microenvironment. These localised responses serve to attract additional immune cells which can reach in excess of 1 × 105 immune cell/mm3 of skeletal muscle in order to orchestrate the repair process. T-cells have a delayed response, reaching peak activation roughly 4 days after the initial damage. The cytokines and growth factors released by activated T-cells play a key role in muscle satellite cell proliferation and migration, although the precise mechanisms of these interactions remain unclear. T-cells in older people display limited ability to activate satellite cell proliferation and migration which is likely to contribute to insufficient muscle repair and, consequently, muscle wasting and weakness. If the factors released by T-cells to activate satellite cells can be identified, it may be possible to develop therapeutic agents to enhance muscle regeneration and reduce the impact of muscle wasting during ageing and disease
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