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  • 1
    ISSN: 1420-9136
    Keywords: wave propagation ; linear Rossby wave theory ; stratospheric planetary waves ; potential vorticity ; passive tracers ; critical layers ; wave breaking ; wave mean-flow interaction ; reversibility
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A recently proposed general definition of wave breaking is further discussed, in order to deal with some points on which misunderstanding appears to have arisen. As with surface and internal gravity waves, the classification of Rossby waves into ‘breaking’ and ‘not breaking’ is a generic classification based on dynamical considerations, and not a statement about any unique ‘signature’ or automatically recognizable shape. Nor is it a statement about passive tracers uncorrelated with potential vorticity on isentropic surfaces. A strong motivation for the definition is that proofs of the ‘nonacceleration’ theorem of wave, mean-flow interaction theory rely, explicitly or implicitly, on a hypothesis that the waves do not ‘break’ in the sense envisaged. The general definition refers to the qualitative behaviour of a certain set of material contours, namely those, and only those, which would undulate reversibly, with small ‘slopes’, under the influence of the waves' restoring mechanism, in those circumstances for which linearized, nondissipative wave theory is a self-consistent approximation to nonlinear reality. The waves' restoring mechanism depends upon the basic-state vertical potential density gradient in the case of gravity waves, and upon the basic-state isentropic gradient of potential vorticity in the case of Rossby waves. In the usual linearized theory of planetary scale Rossby waves on a zonal shear flow, the relevant material contours lie along latitude circles when undisturbed.
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  • 2
    ISSN: 1369-1600
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The amino acid L-glutamine is essential for the function of both resting and stimulated lymphocytes, and its uptake is significantly increased after stimulation. The effects of ethanol on the immune system appear to be widespread and significant, and its role as an osmolyte has recently been proposed to be important. The in vitro effect of concurrent glutamine deprivation and ethanol exposure in different osmotic conditions was investigated with respect to the proliferative capability of lymphocytes in vitro from both alcohol abusers and non-abusers, and also the kinetics of glutamine transport across peripheral blood lymphocytes (PBL) membranes from non-abusers. In a physiologically normal situation ethanol increases osmolality, and tonicity remains balanced. However, in situations of electrolyte imbalance ethanol addition may result in osmolality remaining near normal levels, but with hypotonicity. It was found that a lack of glutamine and iso-osmotic hypotonic high ethanol concentrations caused a greater inhibition of mitogen-stimulated lymphocyte proliferation than either factor alone. This was true for PBL from both non-abusers and abusers of alcohol. There was no change in membrane permeability and active transport of glutamine into lymphocytes from non-abusers that were stimulated in vitro in various conditions of ethanol, osmolality and tonicity. While lymphocyte proliferation may be inhibited in certain conditions and this is further affected by a lack of glutamine, the capacity for active glutamine transport was maintained, perhaps due to its essential role in lymphocyte metabolism.
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Addiction biology 5 (2000), S. 0 
    ISSN: 1369-1600
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The alterations in the immune system caused by ethanol appear to be a complex combination of direct and indirect effects. The role of ethanol as an osmolyte has previously been studied in this laboratory with rat splenocytes. In the present study the osmotic effects of ethanol were investigated in lymphocytes from human normal subjects and alcohol abusers. Mitogen-stimulated lymphocytes were cultured in vitro with ethanol in hyperosmotic isotonic or iso-osmotic hypotonic conditions. The former conditions mimic the physiological situation where ethanol increases osmolality in an electrolyte-balanced environment. Under these conditions, lymphocyte proliferation was unaffected. Ethanol addition in iso-osmotic hypotonic conditions, where there is electrolyte imbalance, was associated with inhibition of T-lymphocyte proliferation. Hyperosmotic hypertonic solutions in the absence of ethanol also resulted in inhibition of T-lymphocyte proliferation. Electron microscopy and measurement of cell viability and metabolic activity (lactate and ATP levels) indicated that the decreased proliferation associated with NaCl-induced hyperosmotic hypertonic conditions was at least partially attributable to cell death together with, and possibly caused by, detrimental effects on mitochondria. Conversely, decreased T-lymphocyte proliferation in iso-osmotic hypotonic high ethanol solutions, appeared not to be due to changes in cell viability, nor alterations to energy metabolism. It is proposed that ion fluxes involved in the maintenance of cell volume, in particular K + movement, may be important in facilitating normal lymphocyte proliferation in the presence of ethanol in pathological conditions associated with electrolyte imbalance.
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Addiction biology 2 (1997), S. 0 
    ISSN: 1369-1600
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: While there have been reports on the in vitro effects of ethanol on mitogen-stimulated lymphocyte proliferation, little attention has been paid to whether these effects are mediated by the ethanol molecule per se or the associated hyperosmolality. There is controversy whether ethanol at high concentrations inhibits or has no effect on mitogen-stimulated proliferation of T cells. In this study we sought to distinguish between effects due to ethanol and those related to increased osmolality. Rat splenocytes were cultured in vitro in hypertonic (320 mOsm) or isotonic (320 mOsm) ethanol solutions (up to 400 mg/dL), or in corresponding hypertonic solutions without ethanol. Proliferative responses to the B cell mitogen lipopolysaccharide and the T cell mitogen concanavalin A were measured by mitochondrial dimethylthiazole diphenyl tetrazolium metabolism and [3H]-thymidine incorporation into DNA. B cell response was not significantly affected by ethanol under any conditions. By contrast, T cell proliferative responses were significantly inhibited by isotonic ethanol solutions or hypertonic solutions in the absence of ethanol, but not by hypertonic ethanol solutions. These results indicate that, while high osmolality is normally inhibitory to lymphocyte function, the increase in osmolality caused by ethanol is protective against the otherwise detrimental effects of ethanol.
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  • 5
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The ability of 15 atmospheric general circulation models (AGCM) to simulate the tropical intraseasonal oscillation has been studied as part of the Atmospheric Model Intercomparison Project (AMIP). Time series of the daily upper tropospheric velocity poential and zonal wind, averaged over the equatorial belt, were provided from each AGCM simulation. These data were analyzed using a variety of techniques such as time filtering and space-time spectral analysis to identify eastward and westward moving waves. The results have been compared with an identical assessment of the European Centre for Medium-range Weather Forecasts (ECMWF) analyses for the period 1982–1991. The models display a wide range of skill in simulating the intraseasonal oscillation. Most models show evidence of an eastward propagating anomaly in the velocity potential field, although in some models there is a greater tendency for a standing oscillation, and in one or two the field is rather chaotic with no preferred direction of propagation. Where a model has a clear eastward propagating signal, typical periodicities seem quite reasonable although there is a tendency for the models to simulate shorter periods than in the ECMWF analyses, where it is near 50 days. The results of the space-time spectral analysis have shown that no model has captured the dominance of the intraseasonal oscillation found in the analyses. Several models have peaks at intraseasonal time scales, but nearly all have relatively more power at higher frequencies (〈 30 days) than the analyses. Most models underestimate the strength of the intraseasonal variability. The observed intraseasonal oscillation shows a marked seasonality in its occurrence with greatest activity during northern winter and spring. Most models failed to capture this seasonality. The interannual variability in the activity of the intraseasonal oscillation has also been assessed, although the AMIP decade is too short to provide any conclusive results. There is a suggestion that the observed oscillation was suppressed during the strong El Niño of 1982/83, and this relationship has also been reproduced by some models. The relationship between a model's intraseasonal activity, its seasonal cycle and characteristics of its basic climate has been examined. It is clear that those models with weak intraseasonal activity tend also to have a weak seasonal cycle. It is becoming increasingly evident that an accurate description of the basic climate may be a prerequisite for producing a realistic intraseasonal oscillation. In particular, models with the most realistic intraseasonal oscillations appear to have precipitation distributions which are better correlated with warm sea surface temperatures. These models predominantly employ convective parameterizations which are closed on buoyancy rather than moisture convergence.
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  • 6
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract. The ability of 15 atmospheric general circulation models (AGCM) to simulate the tropical intraseasonal oscillation has been studied as part of the Atmospheric Model Intercomparison Project (AMIP). Time series of the daily upper tropospheric velocity poential and zonal wind, averaged over the equatorial belt, were provided from each AGCM simulation. These data were analyzed using a variety of techniques such as time filtering and space-time spectral analysis to identify eastward and westward moving waves. The results have been compared with an identical assessment of the European Centre for Medium-range Weather Forecasts (ECMWF) analyses for the period 1982–1991. The models display a wide range of skill in simulating the intraseasonal oscillation. Most models show evidence of an eastward propagating anomaly in the velocity potential field, although in some models there is a greater tendency for a standing oscillation, and in one or two the field is rather chaotic with no preferred direction of propagation. Where a model has a clear eastward propagating signal, typical periodicities seem quite reasonable although there is a tendency for the models to simulate shorter periods than in the ECMWF analyses, where it is near 50 days. The results of the space-time spectral analysis have shown that no model has captured the dominance of the intraseasonal oscillation found in the analyses. Several models have peaks at intraseasonal time scales, but nearly all have relatively more power at higher frequencies (〈30 days) than the analyses. Most models underestimate the strength of the intraseasonal variability. The observed intraseasonal oscillation shows a marked seasonality in its occurrence with greatest activity during northern winter and spring. Most models failed to capture this seasonality. The interannual variability in the activity of the intraseasonal oscillation has also been assessed, although the AMIP decade is too short to provide any conclusive results. There is a suggestion that the observed oscillation was suppressed during the strong El Niño of 1982/83, and this relationship has also been reproduced by some models. The relationship between a model's intraseasonal activity, its seasonal cycle and characteristics of its basic climate has been examined. It is clear that those models with weak intraseasonal activity tend also to have a weak seasonal cycle. It is becoming increasingly evident that an accurate description of the basic climate may be a prerequisite for producing a realistic intraseasonal oscillation. In particular, models with the most realistic intraseasonal oscillations appear to have precipitation distributions which are better correlated with warm sea surface temperatures. These models predominantly employ convective parameterizations which are closed on buoyancy rather than moisture convergence.
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  • 7
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 434 (2005), S. 271-271 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Sir By using the distributed power of personal computers around the planet, D. A. Stainforth and colleagues (Nature 433, 403–406; 2005) have quantified uncertainty in forecasts of global warming resulting from a ...
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  • 8
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 338 (1989), S. 54-57 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The El Nifio event in the tropical Pacific ocean is now recognized as part of the natural variability of the coupled ocean-atmosphere system3. At its height, the El Nino event is associated with an anomalous warming of the surface waters of the east and central tropical Pacific. There have been ...
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  • 9
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 320 (1986), S. 602-607 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Fig. 1 a, Standardized annual rainfall anomalies for the Sahel, 1901-85 (upper panel). Values to 1984 are after Nicholson11; 1985 values are from CLIMAT reports. The lower panel gives the numbers of stations used. 6, SST anomalies (relative to 1951-80), for July to September 1901-85. Solid line, ...
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  • 10
    Electronic Resource
    Electronic Resource
    [s.l.] : Macmillian Magazines Ltd.
    Nature 415 (2002), S. 512-514 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Increasing concentrations of atmospheric carbon dioxide will almost certainly lead to changes in global mean climate. But because—by definition—extreme events are rare, it is significantly more difficult to quantify the risk of extremes. Ensemble-based probabilistic predictions, as ...
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