The sensitivity of the tropical circulation and Maritime Continent precipitation to climate model resolution

The dependence of the annual mean tropical precipitation on horizontal resolution is investigated in the atmospheric version of the Hadley Centre General Environment Model (HadGEM1). Reducing the grid spacing from about 350 km to 110 km improves the precipitation distribution in most of the tropics. In particular, characteristic dry biases over South and Southeast Asia including the Maritime Continent as well as wet biases over the western tropical oceans are reduced. The annual-mean precipitation bias is reduced by about one third over the Maritime Continent and the neighbouring ocean basins associated with it via the Walker circulation. Sensitivity experiments show that much of the improvement with resolution in the Maritime Continent region is due to the specification of better resolved surface boundary conditions (land fraction, soil and vegetation parameters) at the higher resolution. It is shown that in particular the formulation of the coastal tiling scheme may cause resolution sensitivity of the mean simulated climate. The improvement in the tropical mean precipitation in this region is not primarily associated with the better representation of orography at the higher resolution, nor with changes in the eddy transport of moisture. Sizeable sensitivity to changes in the surface fields may be one of the reasons for the large variation of the mean tropical precipitation distribution seen across climate models

Climate simulations for 1880-2003 with GISS modelE

We carry out climate simulations for 1880-2003 with GISS modelE driven by ten measured or estimated climate forcings. An ensemble of climate model runs is carried out for each forcing acting individually and for all forcing mechanisms acting together. We compare side-by-side simulated climate change for each forcing, all forcings, observations, unforced variability among model ensemble members, and, if available, observed variability. Discrepancies between observations and simulations with all forcings are due to model deficiencies, inaccurate or incomplete forcings, and imperfect observations. Although there are notable discrepancies between model and observations, the fidelity is sufficient to encourage use of the model for simulations of future climate change. By using a fixed well-documented model and accurately defining the 1880-2003 forcings, we aim to provide a benchmark against which the effect of improvements in the model, climate forcings, and observations can be tested. Principal model deficiencies include unrealistically weak tropical El Nino-like variability and a poor distribution of sea ice, with too much sea ice in the Northern Hemisphere and too little in the Southern Hemisphere. The greatest uncertainties in the forcings are the temporal and spatial variations of anthropogenic aerosols and their indirect effects on clouds.Comment: 44 pages; 19 figures; Final text accepted by Climate Dynamic

Who’s looking at who?

Object abuse: beyond tools, beyond brands, beyond auratic fetishism. A symposium event This event will consider a less-explored reading of objects and things, questioning our relation with them and exploring the potential of other forms of address. We suggest that a new intention needs to be employed to interrogate our role in relations with objects; that in object abuse there lies the question of who or what is abused. Does co-presence allow another position, redressing our intentions and interactions – who’s looking at who? Might the animistic gaze reveal objects to be more than tools or resources? Or are we blinded by our fetishes?* Three speakers, from different disciplines, will present a provocation in response to this question. An Open Space process will be engaged in for the assembled audience and speakers to address this question. People will participate in an active way, producing a dynamic debate. Participants will be co-present in a non-hierarchial structure. *’They (the Moderns) do have a fetish, the strangest one of all: they deny to the objects they fabricate the autonomy they have given them. They pretend they are not surpassed, outstripped by events. They want to keep their mastery, and they find its source within the human subject, the origin of action’. Bruno Latour, On the Modern Cult of the Factish Gods </p

Quantitative analysis of voltage-gated potassium currents from primary equine (Equus caballus) and elephant (Loxodonta africana) articular chondrocytes.

In this comparative study, we have established in vitro models of equine and elephant articular chondrocytes, examined their basic morphology, and characterized the biophysical properties of their primary voltage-gated potassium channel (Kv) currents. Using whole cell patch-clamp electrophysiological recording from first-expansion and first-passage cells, we measured a maximum Kv conductance of 0.15 +/- 0.04 pS/pF (n = 10) in equine chondrocytes, whereas that in elephant chondrocytes was significantly larger (0.8 +/- 0.4 pS/pF, n = 4, P </= 0.05). Steady-state activation parameters of elephant chondrocytes (V = -22 +/- 6 mV, k = 11.8 +/- 3 mV, n = 4) were not significantly different from those of horse chondrocytes (V = -12.5 +/- 4.3 mV, k = 12 +/- 2, n = 10). This suggests that there would be slightly more resting Kv activation in elephant chondrocytes than in their equine counterparts. Kinetic analysis revealed that both horse and elephant chondrocyte Kv currents had similar activation and inactivation parameters. Pharmacological investigation of equine chondrocyte Kv currents showed them to be powerfully inhibited by the potassium channel blockers tetraethylammonium and 4-aminopyridine but not by dendrotoxin-I. Immunohistochemical studies using polyclonal antibodies to Kv1.1-Kv1.5 provided evidence for expression of Kv1.4 in equine chondrocytes. This is the first electrophysiological study of equine or elephant chondrocytes. The data support the notion that voltage-gated potassium channels play an important role in regulating the membrane potential of articular chondrocytes and will prove useful in future modeling of electromechanotransduction of fully differentiated articular chondrocytes in these and other species

Evidence for functional ATP-sensitive (K(ATP)) potassium channels in human and equine articular chondrocytes.

OBJECTIVE: Chondrocytes are highly sensitive to variations in extracellular glucose and oxygen levels in the extracellular matrix. As such, they must possess a number of mechanisms to detect and respond to alterations in the metabolic state of cartilage. In other organs such as the pancreas, heart and brain, such detection is partly mediated by a family of potassium channels known as K(ATP) (adenosine 5'-triphosphate-sensitive potassium) channels. Here we investigate whether chondrocytes too express functional K(ATP) channels, which might, potentially, serve to couple metabolic state with cell activity. METHODS: Immunohistochemistry was used to explore K(ATP) channel expression in equine and human chondrocytes. Biophysical properties of equine chondrocyte K(ATP) channels were investigated with patch-clamp electrophysiology. RESULTS: Polyclonal antibodies directed against the K(ATP) Kir6.1 subunit revealed high levels of expression in human and equine chondrocytes mainly in superficial and middle zones of normal cartilage. Kir6.1 was also detected in superficial chondrocytes in osteoarthritic (OA) cartilage. In single-channel electrophysiological studies of equine chondrocytes, we found K(ATP) channels to have a maximum unitary conductance of 47 +/- 9 pS (n=5) and a density of expression comparable to that seen in excitable cells. CONCLUSION: We have shown, for the first time, functional K(ATP) channels in chondrocytes. This suggests that K(ATP) channels are involved in coupling metabolic and electrical activities in chondrocytes through sensing of extracellular glucose and intracellular adenosine triphosphate (ATP) levels. Altered K(ATP) channel expression in OA chondrocytes may result in impaired intracellular ATP sensing and optimal metabolic regulation

Deficiencies in numerical models of anisotropic nonlinearly elastic materials

Incompressible nonlinearly hyperelastic materials are rarely simulated in finite element numerical experiments as being perfectly incompressible because of the numerical difficulties associated with globally satisfying this constraint. Most commercial finite element packages therefore assume that the material is slightly compressible. It is then further assumed that the corresponding strain-energy function can be decomposed additively into volumetric and deviatoric parts. We show that this decomposition is not physically realistic, especially for anisotropic materials, which are of particular interest for simulating the mechanical response of biological soft tissue. The most striking illustration of the shortcoming is that with this decomposition, an anisotropic cube under hydrostatic tension deforms into another cube instead of a hexahedron with non-parallel faces. Furthermore, commercial numerical codes require the specification of a 'compressibility parameter' (or 'penalty factor'), which arises naturally from the flawed additive decomposition of the strain-energy function. This parameter is often linked to a 'bulk modulus', although this notion makes no sense for anisotropic solids; we show that it is essentially an arbitrary parameter and that infinitesimal changes to it result in significant changes in the predicted stress response. This is illustrated with numerical simulations for biaxial tension experiments of arteries, where the magnitude of the stress response is found to change by several orders of magnitude when infinitesimal changes in 'Poisson's ratio' close to the perfect incompressibility limit of 1/2 are made

Microstructure and tensile mechanical properties of anisotropic rigid polyurethane foam

10.1007/s11340-008-9146-0Experimental Mechanics486763-776EXMC