ULTRASONIC VELOCITIES OF CHALK SAMPLES: INFLUENCE OF POROSITY, FLUID CONTENT AND TEXTURE

ABSTRACT The acoustic properties of the pure chalk of the Upper Cretaceous Tor Formation have been studied on core material from the Dan and South Arne fields, Danish North Sea. Detailed investigations were carried out on 56 vertical plug samples with porosities ranging from 14% to 45%, i.e. measurement of P-and S-wave velocities of dry and water-wet samples and microtextural image analysis on backscatter micrographs. Porosity is the primary control on sonic velocities and elastic moduli of chalk with identical pore fluids. For chalk samples dominated by fine carbonate particles (mud) we obtain a well-defined relation between elastic moduli and porosity, which can be modeled using a modified upper Hashin-Shtrikman bound. The trend is defined by a bulk and shear modulus at zero porosity of 54 and 22 GPa, and by a high-porosity end-member at 47%. We find that compaction, grain size distribution, and possibly mineralogy, rather than pore-filling cementation, control the variation of porosity for the samples. Variations in chalk particle size distribution and the content of non-carbonates influence the relation between elastic properties and porosity for the samples investigated even though the carbonate content is >95%. South Arne samples are found to be stiffer than Dan/Gorm samples for identical porosities e.g. a porosity of 30% corresponds on average to a bulk modulus of 17 GPa and 14 GPa, respectively, for the saturated samples. Conversely, a bulk modulus of 15 GP

Lipolysis drives expression of the constitutively active receptor GPR3 to induce adipose thermogenesis

Thermogenic adipocytes possess a therapeutically appealing, energy-expending capacity, which is canonically cold-induced by ligand-dependent activation of β-adrenergic G protein-coupled receptors (GPCRs). Here, we uncover an alternate paradigm of GPCR-mediated adipose thermogenesis through the constitutively active receptor, GPR3. We show that the N terminus of GPR3 confers intrinsic signaling activity, resulting in continuous Gs-coupling and cAMP production without an exogenous ligand. Thus, transcriptional induction of Gpr3 represents the regulatory parallel to ligand-binding of conventional GPCRs. Consequently, increasing Gpr3 expression in thermogenic adipocytes is alone sufficient to drive energy expenditure and counteract metabolic disease in mice. Gpr3 transcription is cold-stimulated by a lipolytic signal, and dietary fat potentiates GPR3-dependent thermogenesis to amplify the response to caloric excess. Moreover, we find GPR3 to be an essential, adrenergic-independent regulator of human brown adipocytes. Taken together, our findings reveal a noncanonical mechanism of GPCR control and thermogenic activation through the lipolysis-induced expression of constitutively active GPR3.ISSN:0092-8674ISSN:1097-417

Ensemble approach to simulated annealing

We present three reasons for implementing simulated annealing with an ensemble of random walkers which search the configuration space in parrallel. First, an ensemble allows the implementation of an adaptive cooling schedule because it provides good statistics for collecting thermodynamic information. This new adaptive implementation is general, simple, and, in some sense, optimal. Second, the ensemble can tell us how to optimally allocate our effort in the search for a good solution, i.e., given the total computer time available, how many members to use in the ensemble. Third, an ensemble can reveal otherwise hidden properties of the configuration space, e.g., by examining Hamming distance distributions among the ensemble members. We present numerical results on the bipartitioning of random graphs and on a graph bipartitioning problem whose static thermodynamic properties may be solved for exactly

On lumped models for thermodynamic properties of simulated annealing problems

The paper describes a new method for the estimation of thermodynamic properties for simulated annealing problems using data obtained during a simulated annealing run. The method works by estimating energy-to-energy transition probabilities and is well adapted to simulations such as simulated annealing, in which the system is never in equilibrium.Nous décrivons une nouvelle méthode pour estimer les propriétés thermodynamiques dans des problèmes de recuit simulé, méthode qui utilise des données acquises durant le recuit simulé. La méthode est basée sur l' estimation des probabilités de transition énergie-énergie et est bien adaptée à des simulations de type recuit simulé, dans lesquelles le système n'est jamais à l'équilibre