Volume 32, Issue 1

Physical, mathematical, and observational grounds are employed to show that there is no physically meaningful global temperature for the Earth in the context of the issue of global warming. While it is always possible to construct statistics for any given set of local temperature data, an infinite range of such statistics is mathematically permissible if physical principles provide no explicit basis for choosing among them. Distinct and equally valid statistical rules can and do show opposite trends when applied to the results of computations from physical models and real data in the atmosphere. A given temperature field can be interpreted as both “warming” and “cooling” simultaneously, making the concept of warming in the context of the issue of global warming physically ill-posed.

When making the connection between the thermodynamics of irreversible processes and the theory of stochastic processes through the fluctuation–dissipation theorem, it is necessary to invoke a postulate of the Einstein–Boltzmann type. For convective processes hydrodynamic fluctuations must be included; the velocity is a dynamical variable and although the entropy cannot depend directly on the velocity, δ 2 S will depend on velocity variations. Some authors do not include velocity variations in δ 2 S , and so have to introduce a non-thermodynamic function which replaces the entropy and does depend on the velocity. At first sight, it seems that the introduction of such a function requires a generalisation of the Einstein–Boltzmann relation to be invoked. We review the reason why it is not necessary to introduce such a function, and therefore why there is no need to generalise the Einstein–Boltzmann relation in this way. We then obtain the fluctuation–dissipation theorem, which shows some differences as compared with the non-convective case. We also show that δ 2 S is a Liapunov function when it includes velocity fluctuations.

Besides temperature, we used hydrostatic pressure as a physical parameter for studying the stability and energetics of biomolecular systems. High pressure is also an important feature of certain natural environments, and the high-pressure phase behaviour of biomolecules is of increasing biotechnological interest. By using thermodynamic, spectroscopic, and scattering techniques, the temperature and pressure-dependent structure and phase behaviour of model biomembrane systems and proteins have been studied. The results demonstrate that combined temperature–pressure-dependent studies can help delineate the conformational and free-energy landscape of biomolecules and hence help to elucidate which features and thermodynamic parameters are essential in determining their stability. Moreover, we present data on the effect of various types of cosolvents on the temperature- and pressure-dependent structure and stability of proteins. We also introduce pressure as a kinetic variable. Applying the pressure-jump relaxation technique in combination with time-resolved synchrotron X-ray diffraction and spectroscopic techniques, the kinetics of lipid phase transitions and un/refolding reactions of proteins have been studied. Finally, recent advances in using the pressure axis for studying misfolding, aggregation, and amyloid fibril formation of proteins and its potential biotechnological and biomedical relevance will be discussed. We conclude with an outlook of the perspectives of high pressure research.