Fine structure of laboratory wind-wave surfaces studied using an optical method

The fine structure of laboratory wind-wave surfaces was investigated using an optical method. Several characteristic structures, closely associated with wind speed and the stage of development of the waves, are described. A parallel light, incident on the wind-wave surface, was backscattered by specular facets perpendicular to the incident angle. These specular facets, which represented the fine structures, were photographed and quantitatively analyzed by image processing techniques.For wind speeds ranging from 3.6 to 13.6 m s^–1, different types of small-scale undulations appeared: a three-dimensional rhombic structure; a train of capillary waves on the forward face with wavelengths gradually decreasing with distance from the crest, and a streaky structure on the backward face in the direction of the wind; and random and wide-spreading irregularities covering the whole wind-wave surface. The spatial scales and temporal variation of the undulations are described.     

Large strain analysis of some geomechanics problems by the finite element method

This paper presents a rational approach to the finite strain analysis of elastic-plastic materials. An updated incremental finite element technique was applied to problems of shallow foundations of homogeneous as well as multilayer soils. This was based on a variational principle which is suitable for such problems.     

Eigenvalues and eigenvectors for hybrid coordinate equations of motion for flexible spacecraft

Literal characterizations are developed for the eigenvalues and eigenvectors of a system of linear time-invariant equations which describes the attitude motion of flexible spacecraft in terms of hybrid coordinates. The eigenproblem is shown to reduce to that of a symmetric and positive definite matrix of lower dimension. For the zero damping case, both analytical and minimax characterization methods prove to be useful in localizing the eigenvalues, and eigenvectors for systems of large dimension are obtained explicitly in terms of a 3×1 matrix whose elements are available from a system of three algebraic equations provided.     

Investigation of cutting methods for small samples of Hayabusa and future sample return missions

We report the investigation of cutting methods for Hayabusa samples. The purpose of our study is to explore the possibility of applying multiple analyses to a single particle effectively. We investigated the cutting performance of a blade dicing saw, laser, focused ion beam (FIB), and physical breaking by microindenter. Cutting performance was examined by estimating the aspect ratio of the cut slit, i.e., depth over width of the slit. We also investigated the possible contamination and sample damage by cutting. The result of the investigation shows that we can cut the samples from <50 μm to 500 μm using those methods with aspect ratios from 10 to 20, although they would introduce some contamination or damage to the samples. Our investigations also provide an important basis for the analysis of samples obtained by future sample return missions.     

Low-Luminosity Extra-Galactic H2O Masers

Recent high-resolution observations of low-luminosity extra-galactic H₂O masers towards M 82, M 51, and NGC 4051 are presented in this contribution. These observations were conducted using the very large array (VLA). The general observational properties of these masers are discussed.     

Statistical properties of microwave backscattering from laboratory wind-wave surfaces

The microwave backscattering from wind-wave surfaces is observed in a windwave tunnel under various conditions of the wind and wind waves, and its statistical features are investigated. The dependence of the backscattered power on the wind speed and the incident angle shows similar features to those predicted by models proposed previously. However, the dependence of the backscattered power on the incident angles also corresponds to the asymmetrical feature of the wind-wave surfaces with respect to the wind direction. The spectral analyses of time series of the backscattered intensity show that the propagating speed of fine structures of the wind-wave surface contributing to the backscattering at large incident angles does not coincide with the phase speed of the freely propagating Braggwaves. Atupwind incidence, the surface structures of wind waves contributing to the backscattering propagates with the dominant waves at their phase speed. This result is inconsistent with the two-scale model in which the Bragg waves are simply superimposed on longer waves, but is consistent with the results of optical observation by Ebuchiet al. (1987). At downwind incidence, the propagating speed is slower than the phase speed of the dominant waves.     

The steepness and shape of wind waves

Variations are found in the shape and the steepness of wind-generated surface gravity waves between very young waves, such as seen in a laboratory tank, and larger waves of various wave ages encountered at sea as the result of wind stress over larger fetches. These differences in the characteristic shape of wind waves are presented as a function of the wave age. The wave steepness is also expressed as a function of wave age, the measurement of which is consistent with the 3/2-power law connecting wave height and characteristic period, normalized by the air friction velocity.     

Pan-African Alkali Granitoids from the Sør Rondane Mountains, East Antarctica

Alkali granitoids (500-550 Ma) representing a prominent Pan-African magmatic event are widely distributed in the Sør Rondane Mountains, Dronning Maud Land, East Antarctica. Geochemically, they are granitic to syenitic in composition and show an alkaline affinity of A-type granites. They are characterized by high K₂O+Na₂O (7-13 wt%) and K₂O/Na₂O (1-2), low to intermediate Mg#, wide ranges of SiO₂ (45-78 wt%), Sr (20-6500 ppm) and Ba (40-13000 ppm) and have Nb and Ti depletion in the primitive mantle normalized diagram. The granitoids are subdivided into Group I granites, Group II granites, Lunckeryggen Syenitic Complex and Mefjell Plutonic Complex. The Group I granites have higher Mg#, Sr/Ba, Sr/Y, (La/Yb)_N and LREE/HREE, lower A/CNK, SREE and initial ⁸⁷Sr/⁸⁷Sr ratios and lack Eu anomalies compared to those with negative Eu anomalies in the Group II granites. The syenitic rocks from the Mefjell Plutonic Complex are higher in alkali, Ga, Zr, Ba, and have lower Mg#, Rb, Sr, Nb, Y, F and LREE/HREE with positive Eu anomaly, whereas the granites from the Mefjell Plutonic Complex have high LREE/HREE ratios with negative Eu anomaly. The Lunckeryggen syenitic rocks have intermediate Mg#, higher K₂O, P₂O₅, TiO₂, Fe₂O₃/FeO, Ba, Sr/Y and LREE/HREE ratios with lack of Eu anomalies and are lower in Al₂O₃, Ga, Y, Nb and Rb/Sr ratios. Based on chemical characteristics combined with isotopic data, we suggest that the Lunckeryggen syenitic body and Group I granitic bodies may be derived from the mantle-derived hot basic magma by fractional crystallization with minor assimilation. We also suggest that the Group II granites may be derived from assimilation with crustal rocks to varing degrees and then fractional crystallization in higher crustal levels (ACF model). The Mefjell Plutonic Complex seems to be derived from a heterogenetic magma source compared with other granitoids from the Sør Rondane Mountains. The syenitic rocks in the Mefjell Plutonic complex have a unique source (iron-enriched) and have a chemical affinity with the charnockites in Gjelsvikjella and western Mühlig-Hofmannfjella, but not like the Yamato syenites in adjacent areas.     

A Spectral Approach for Determining Altimeter Wind Speed Model Functions

We propose a new analytical algorithm for the estimation of wind speeds from altimeter data using the mean square slope of the ocean surface, which is obtained by integration of a widely accepted wind-wave spectrum including the gravity-capillary wave range. It indicates that the normalized radar cross section depends not only on the wind speed but also on the wave age. The wave state effect on the altimeter radar return becomes remarkable with increasing wind speed and cannot be neglected at high wind speeds. A relationship between wave age and nondimensional wave height based on buoy observational data is applied to compute the wave age using the significant wave height of ocean waves, which could be simultaneously obtained from altimeter data. Comparison with actual data shows that this new algorithm produces more reliable wind speeds than do empirical algorithms. This revised version was published online in July 2006 with corrections to the Cover Date.