Terrestrial – Ocean environmental change in the northwestern Pacific from the glacial times to Holocene

The Mixed Water Region (MWR) between the Oyashio Current and the Kuroshio Extension and surrounding terrestrial region have been affected by the global climatic change. The sedimentary core KR02-15 PC6 collected at 40°23.8871′N, 143°29.8663′E in the MWR provides detailed records of pollen and spores and alkenone sea surface temperature (SST) during the last 15 kyr, showing that both ocean and terrestrial environments have been appreciably linked. Abundance of Picea, a proxy for terrestrial cool climate, fluctuated, coinciding with the alkenone-SST change during the interstadial period (15.0–7.7 cal kyr B.P.). Alkenone-SST increased to the modern level at 8.0 cal kyr B.P. and remained almost constant until 2.0 kyr B.P. while the terrestrial warming still continued until 4.0 cal kyr B.P. The rainfall under terrestrial warm condition increased gradually from 7.9 cal kyr B.P. and rapidly from 2.0 cal kyr B.P. Both terrestrial and marine environments cooled down during the last 2 kyr possibly due to the intensified cold Oyashio Current.     

Statistical distribution of gravitational-lensing excursion angles: winding ways to us from the deep Universe

We investigate statistical distributions of differences in gravitational-lensing deflections between two light rays, the so-called lensing excursion angles. A probability distribution function of the lensing excursion angles, which plays a key role in estimates of lensing effects on angular clustering of objects (such as galaxies, quasi-stellar objects and also the cosmic microwave background temperature map), is known to consist of two components: a Gaussian core and an exponential tail. We use numerical gravitational-lensing experiments in a ΛCDM cosmology for quantifying these two components. We especially focus on the physical processes responsible for generating these two components. We develop a simple empirical model for the exponential tail which allows us to explore its origin. We find that the tail is generated by the coherent lensing scatter by massive haloes with   M > 10¹⁴  h ⁻¹ M_⊙  at   z < 1  and that its exponential shape arises due to the exponential cut-off of the halo mass function at that mass range. On scales larger than 1 arcmin, the tail does not have a practical influence on the lensing effects on the angular clustering. Our model predicts that the coherent scatter may have non-negligible effects on angular clustering at subarcminute scales.     

Quasi-radial modes of rotating stars in general relativity

By using the Cowling approximation, quasi-radial modes of rotating general relativistic stars are computed along equilibrium sequences from non-rotating to maximally rotating models. The eigenfrequencies of these modes are decreasing functions of the rotational frequency. The eigenfrequency curve of each mode as a function of the rotational frequency has discontinuities, which arise from the avoided crossing with other curves of axisymmetric modes.     

Can non-Gaussian cosmological models explain the WMAP high optical depth for reionization?

The first-year Wilkinson Microwave Anisotropy Probe data suggest a high optical depth for Thomson scattering of  0.17 ± 0.04  , implying that the Universe was reionized at an earlier epoch than previously expected. Such early reionization is likely to be caused by ultraviolet (UV) photons from first stars, but it appears that the observed high optical depth can be reconciled within the standard structure formation model only if star formation in the early Universe was extremely efficient. With normal star formation efficiencies, cosmological models with non-Gaussian density fluctuations may circumvent this conflict as high density peaks collapse at an earlier epoch than in models with Gaussian fluctuations. We study cosmic reionization in non-Gaussian models and explore to what extent, within available constraints, non-Gaussianities affect the reionization history. For mild non-Gaussian fluctuations at redshifts of 30 to 50, the increase in optical depth remains at a level of a few per cent and appears unlikely to aid significantly in explaining the measured high optical depth. On the other hand, within available observational constraints, increasing the non-Gaussian nature of density fluctuations can easily reproduce the optical depth and may remain viable in underlying models of non-Gaussianity with a scale-dependence.     

A numerical model simulating reactive transport and evolution of fracture permeability

A numerical model is presented to describe the evolution of fracture aperture (and related permeability) mediated by the competing chemical processes of pressure solution and free‐face dissolution/precipitation; pressure (dis)solution and precipitation effect net‐reduction in aperture and free‐face dissolution effects net‐increase. These processes are incorporated to examine coupled thermo‐hydro‐mechano‐chemo responses during a flow‐through experiment, and applied to reckon the effect of forced fluid injection within rock fractures at geothermal and petroleum sites. The model accommodates advection‐dominant transport systems by employing the Lagrangian–Eulerian method. This enables changes in aperture and solute concentration within a fracture to be followed with time for arbitrary driving effective stresses, fluid and rock temperatures, and fluid flow rates. This allows a systematic evaluation of evolving linked mechanical and chemical processes. Changes in fracture aperture and solute concentration tracked within a well‐constrained flow‐through test completed on a natural fracture in novaculite (Earth Planet. Sci. Lett. 2006, in press) are compared with the distributed parameter model. These results show relatively good agreement, excepting an enigmatic abrupt reduction in fracture aperture in the early experimental period, suggesting that other mechanisms such as mechanical creep and clogging induced by unanticipated local precipitation need to be quantified and incorporated. The model is applied to examine the evolution in fracture permeability for different inlet conditions, including localized (rather than distributed) injection. Predictions show the evolution of preferential flow paths driven by dissolution, and also define the sense of permeability evolution at field scale. Copyright © 2006 John Wiley & Sons, Ltd.     

Finite source effect on the polarization degree induced by a single microlens

We investigate the effect of a single microlens on Stokes parameters. Semi-analytical formulae of the microlensed Stokes parameters are derived. The formulae not only reduce the double integrals in the estimations of those quantities but can also be approximated to a useful form in the bypass case. By using our formulation, we show that a combination of polarimetric data with photometric data enables us to estimate not only the finite source effect but also the direction of the microlens motion.     

Low T/|W| dynamical instability in differentially rotating stars: diagnosis with canonical angular momentum

We study the nature of non-axisymmetric dynamical instabilities in differentially rotating stars with both linear eigenmode analysis and hydrodynamic simulations in Newtonian gravity. We especially investigate the following three types of instability; the one-armed spiral instability, the low   T /| W |  bar instability, and the high   T /| W |  bar instability, where T is the rotational kinetic energy and W is the gravitational potential energy. The nature of the dynamical instabilities is clarified by using a canonical angular momentum as a diagnostic. We find that the one-armed spiral and the low   T /| W |  bar instabilities occur around the corotation radius, and they grow through the inflow of canonical angular momentum around the corotation radius. The result is a clear contrast to that of a classical dynamical bar instability in high   T /| W |  . We also discuss the feature of gravitational waves generated from these three types of instability.