12,643 research outputs found
Response of MarineāTerminating Glaciers to Forcing: Time Scales, Sensitivities, Instabilities, and Stochastic Dynamics
Recent observations indicate that many marineāterminating glaciers in Greenland and Antarctica are currently retreating and thinning, potentially due to longāterm trends in climate forcing. In this study, we describe a simple twoāstage model that accurately emulates the response to external forcing of marineāterminating glaciers simulated in a spatially extended model. The simplicity of the model permits derivation of analytical expressions describing the marineāterminating glacier response to forcing. We find that there are two time scales that characterize the stable glacier response to external forcing, a fast time scale of decades to centuries, and a slow time scale of millennia. These two time scales become unstable at different thresholds of bed slope, indicating that there are distinct slow and fast forms of the marine ice sheet instability. We derive simple expressions for the approximate magnitude and transient evolution of the stable glacier response to external forcing, which depend on the equilibrium glacier state and the strength of nonlinearity in forcing processes. The slow response rate of marineāterminating glaciers indicates that current changes at some glaciers are set to continue and accelerate in coming centuries in response to past climate forcing and that the current extent of change at these glaciers is likely a small fraction of the future committed change caused by past climate forcing. Finally, we find that changing the amplitude of natural fluctuations in some nonlinear forcing processes, such as ice shelf calving, changes the equilibrium glacier state
Minimal kernels of Dirac operators along maps
Let be a closed spin manifold and let be a closed manifold. For maps
and Riemannian metrics on and on , we consider
the Dirac operator of the twisted Dirac bundle . To this Dirac operator one can associate an index
in . If is -dimensional, one gets a lower bound for
the dimension of the kernel of out of this index. We investigate
the question whether this lower bound is obtained for generic tupels
Discovery of Temperate Latitude Clouds on Titan
Until now, all the clouds imaged in Titan's troposphere have been found at far southern latitudes (60Ā°-90Ā° south). The occurrence and location of these clouds is thought to be the result of convection driven by the maximum annual solar heating of Titan's surface, which occurs at summer solstice (2002 October) in this south polar region. We report the first observations of a new recurring type of tropospheric cloud feature, confined narrowly to ~40Ā° south latitude, which cannot be explained by this simple insolation hypothesis. We propose two classes of formation scenario, one linked to surface geography and the other to seasonally evolving circulation, which will be easily distinguished with continued observations over the next few years
A Dynamic CGE Model: An Application of R&D- Based Endogenous Growth Model Theory
An R&D based endogenous growth - applied general equilibrium model is developed from an underlying analytical model which combines Romer's capital variety with Grossman and Helpman's multi-sector open economy model. The transitional dynamics of the analytical model are derived. For numerical implementation, a time discrete empirical model, with an Armington structure, is fit to East Asian data of the social accounting matrix variety. Simulations of trade reform are performed and their static and dynamic effects compared. The transition paths of the state variables are found to have a half-life of five to six periods. A solution of the Social Planner's problem, and interventions which seek to obtain this outcome from the decentralized model are also obtained'.Applied General Equilibrium, Trade, Growth, International Relations/Trade, F11, 031, 041,
Crystal structure of the catalytic fragment of murine poly(ADP-ribose) polymerase-2.
Poly(ADP-ribose) polymerase-1 (PARP-1) has become an important pharmacological target in the treatment of cancer due to its cellular role as a 'DNA-strand break sensor', which leads in part to resistance to some existing chemo- and radiological treatments. Inhibitors have now been developed which prevent PARP-1 from synthesizing poly(ADP-ribose) in response to DNA-breaks and potentiate the cytotoxicity of DNA damaging agents. However, with the recent discoveries of PARP-2, which has a similar DNA-damage dependent catalytic activity, and additional members containing the 'PARP catalytic' signature, the isoform selectivity and resultant pharmacological effects of existing inhibitors are brought into question. We present here the crystal structure of the catalytic fragment of murine PARP-2, at 2.8 A resolution, and compare this to the catalytic fragment of PARP-1, with an emphasis on providing a possible framework for rational drug design in order to develop future isoform-specific inhibitors
A new 1.6-micron map of Titanās surface
We present a new map of Titan's surface obtained in the spectral 'window' at ā¼1.6 Ī¼m between strong methane absorption. This pre-Cassini view of Titan's surface was created from images obtained using adaptive optics on the W.M. Keck II telescope and is the highest resolution map yet made of Titan's surface. Numerous surface features down to the limits of the spatial resolution (ā¼200ā300 km) are apparent. No features are easily identifiable in terms of their geologic origin, although several are likely craters
Direct measurement of the size of 2003 UB313 from the Hubble Space Telescope
We have used the Hubble Space Telescope to directly measure the angular size
of the large Kuiper belt object 2003 UB313. By carefully calibrating the point
spread function of a nearby field star, we measure the size of 2003 UB313 to be
34.31.4 milliarcseconds, corresponding to a diameter of 2400100 km or
a size % larger than Pluto. The V band geometric albedo of 2003 UB313 is
%. The extremely high albedo is consistent with the frosty methane
spectrum, the lack of red coloring, and the lack of observed photometric
variation on the surface of 2003 UB313. Methane photolysis should quickly
darken the surface of 2003 UB313, but continuous evaporation and redeposition
of surface ices appears capable of maintaining the extreme alebdo of this body
Recovery and serious mental illness: a review of current clinical and research paradigms and future directions
Introduction: Recovery from serious mental illness has historically not been considered a likely or even possible outcome. However, a range of evidence suggests the courses of SMI are heterogeneous with recovery being the most likely outcome. One barrier to studying recovery in SMI is that recovery has been operationalized in divergent and seemingly incompatible ways, as an objective outcome, versus a subjective process.
Areas Covered: This paper offers a review of recovery as a subjective process and recovery as an objective outcome; contrasts methodologies utilized by each approach to assess recovery; reports rates and correlates of recovery; and explores the relationship between objective and subjective forms of recovery.
Expert Commentary: There are two commonalities of approaching recovery as a subjective process and an objective outcome: (i) the need to make meaning out of oneās experiences to engage in either type of recovery and (ii) there exist many threats to engaging in meaning making that may impact the likelihood of moving toward recovery. We offer four clinical implications that stem from these two commonalities within a divided approach to the concept of recovery from SMI
- ā¦