Effect of wave amplitude on turbulent flow in a wavy channel by direct numerical simulation

The present study numerically investigates the characteristics of three-dimensional turbulent flow in a wavy channel. For the purpose of a careful observation of the effect of the wave amplitude on the turbulent flow, numerical simulations are performed at a various range of the wave amplitude to wavelength ratio (0.01?α/λ?0.05), where the wavelength is fixed with the same value of the mean channel height (H). The immersed boundary method is used to handle the wavy surface in a rectangular grid system, using the finite volume method. The Reynolds number (Re=U_bH/ν) based on the bulk velocity (U_b) is fixed at 6760. The present computational results for a wavy surface are well compared with those of references. When α/λ=0.02, the small recirculating flow occurs near the trough at the instant, but the mean reverse flow is not observed. In the mean flow field, the reverse flow appears from α/λ=0.03 among the wave amplitude considered in this study. The domain of the mean reverse flow defined by the locations of separation and reattachment depends strongly on the wave amplitude. The pressure drag coefficient augments with increasing the wave amplitude. The friction drag coefficient shows the increase and decrease behavior according to the wave amplitude. The quantitative information about the flow variables such as the distribution of pressure and shear stress on the wavy surface is highlighted.     

The estimation of acid dissociation constants in seawater media from potentionmetric titrations with strong base. I. The ionic product of water — Kw

The various assumptions implicit in the calculation of acid dissociation constants (based on ionic medium standard states) from potentiometric titrations using a cell with liquid junction (i.e. a pH measuring cell) have been examined. It was concluded that results can be obtained having an accuracy commensurate with the experimental precision. It has been shown that although the precise composition of the medium is a function of the hydrogen ion concentration (because of the protolytic nature of some of the ions in the media, e.g., sulphate and fluoride), the effect of such variations in the medium composition can be compensated for when defining the activity of hydrogen ion on an ionic medium standard state by defining the concentration of hydrogen ion as:

where β_HSO4 and β_HF are the relevant association constants and S_T and F_T are the total concentrations of sulphate and fluoride, respectively.This approach was used to obtain values for the ionic product of water (K_W) in artificial seawater media at various temperatures and ionic strengths. These were fitted to give the equation (molal concentration units):

$\text{pK}{}_{\mathrm{w}}\text{=}\text{3441.0}\text{T}\text{+2.256-0.7091}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(}\text{rms deviation 0.01}\text{)}$

where I is the formal ionic strength of the artificial seawater medium and T is the absolute temperature. The values obtained are in reasonable agreement with those found by previous workers.     

Influence of microstructure of loess on triaxial shear strength

Vicksburg loess is characterized by preferred orientation of constituent grains, which on the average dip 4° toward the west (N 80–85°W). This investigation was undertaken to study, quantitatively, the relationship between natural fabric anisotropies of Vicksburg loess and the orientation of applied stress distribution Results of the study indicate the fabric anisotropies in Vicksburg loess are reflected by definite variation in triaxial shear strength of dry and moist specimens.

In two series of triaxial tests, ultimate strength of the loess is maximum where σ₁ is perpendicular to grain orientation, and it is reduced where the principal stresses are 45° to the fabric plane. In this respect, Vicksburg loess may serve as a structural model for granular earth materials in illustrating the influence of fabric on ultimate strength. Moreover, the Mohr-Coulomb fracture line consists of two line segments, with an increase in slope at higher confining pressure. This characteristic suggests that poorly-cemented sands, or sandstones, and silts, or siltstones, may undergo two failures: one at small strains where cement bonds are disrupted and the other at larger strains where internal shearing resistance of granular components is exceeded.     

Some basic notions in geographical synthesis

Modern geography is based on ecological thinking. In this paper some geoecological notions are discussed: the scales and levels regarding spatial magnitude and complexity, the “hierarchy” of landscape units and espcially the scale of time and the concept of the supper-imposing “stamps”. This last mentioned concept is very important in relation to the problem regarding regionalization and its possibilities. Three “stamps” are recognized: 1. the substrate, 2. the climatic conditions, 3. the human (noötic) influence. Holistic regionalization in which all elements (including the human influences) are telling to full advantage, is unsatisfactory.     

Lunar nomenclature: A dissenting note

This note reviews the nature of the traditional (Mädler) lunar nomenclature and the recent developments based on the use of more than 2000 named provinces. It appears that the new nomenclature is less efficient than the old in many cases and may lead to an impossible publication situation. The unnecessary break with the past is especially critized.     

Rms-value and power spectrum of the photospheric intensity-fluctuations

The power spectrum and the rms-value of the granular intensity fluctuations were studied using granulation photographs of excellent quality obtained during the JOSO site testing campaign 1979 at Izaña. The observed power spectrum was corrected using various effective modulation transfer functions of the system: telescope+aberrations+atmospheric seeing, assuming different contributions of the atmospheric seeing. With this procedure a lower and upper limit for the ‘true’ power spectrum of the granular intensity fluctuations and thus for the rms-value could be derived: 7.2% <I _rms <12% at λ = 550 nm, with a most probable value of I _rms = 10.5%. We checked the validity of the upper limit by applying to our data a MTF (Deubner and Mattig, 1975), which certainly must lead to an overcorrection. This procedure lead to I _rms = 13.4%. Thus we can state that the true rms-value of the granular intensity fluctuations does certainly not exceed 13% at λ = 550 nm.     

An Early Investigation Of The Striated Tail Of Comet Hale-Bopp (C/1995 O1)

The Sekanina-Farrell particle fragmentation model for the striated tails of dust comets is successfully applied to two images of comet Hale-Bopp to study the motions of 12 striae in a time span of March 12–15, 1997. There is evidence for recurring outbursts with a periodicity of 11^h21^m, consistent with results based on analysis of dust jets. The ejecta in all the striae appear to have been released from one source on the nucleus between the end of January and the second half of February 1997, some 60 to 40 days before perihelion. The parent particles were subjected to a radiation pressure acceleration of β_p ≃ 0.55 and their fragmentation lifetimes in 11 of the 12 striae were practically constant and equal to 13–15 days, when normalized to 1 AU from the Sun. Brief analysis of Watanabe et al.'s measurements of striae on their images from March 5–9, 1997 shows even shorter fragmentation lifetimes for the parent particles, mostly about 7–11 days at1 AU. This revised version was published online in July 2006 with corrections to the Cover Date.