Core Axis Research Articles

Flowfield of a Rotating-Wing Micro Air Vehicle

Experiments were conducted to measure the performance of a rotor, typical of that used on a rotating-wing micro air vehicle, which was shown to develop relatively low hovering efficiency. This inefficiency can be traced to high profile drag losses on the blades and also to the relatively large turbulent and rotational aerodynamic losses that are associated with the structure of the rotor wake. High-resolution flow visualization images have divulged several interesting flow features that appear unique to rotors operating at low Reynolds numbers. The wake sheets trailing from the rotor blades were found to be much thicker and also more turbulent than their higher chord Reynolds number counterparts. Similarly, the viscous core sizes of the tip vortices were relatively large as a fraction of blade chord. However, the flows in the tip vortices themselves were found to be similar, with laminar flow near their core axis and an outer turbulent region. Particle image velocimetry measurements were made to quantify the structure and strength of the wake flow, including the tip vortices. An analysis of the vortex aging process was conducted. A new nondimensional equivalent time scaling parameter is proposed to normalize the rate of growth of the vortex cores that are generated at substantially different vortex Reynolds numbers.

Stress orientation evaluated from strain localisation analysis in Aigion Fault

Within the frame of the ‘CRL’ (Corinth Rift Laboratory project) [Cornet, F., Bernard, P., Moretti, I., (2004a): The Corinth Rift Laboratory, Comptes Rendus Geosciences, 336, 4–5, 235–242.] centered on the south western sector of the Gulf of Corinth ( http://www.corinth-rift-lab.org), fault zone cores from the active Aigion Fault have been collected continuously from depths between 708 and 782 m. Inside this clayey core, a clear shearing surface with marked slip lines is visible on a plane that makes a 68° angle with respect to the core axis. This failure surface was not induced by the decompression process but is indeed a slip plane as clear striation is observed at the interface. On the basis of an elasto-plastic constitutive model calibrated on triaxial tests on the clayey gouge, it is shown that shear band formation inside the clayey core is possible. The solution for the orientation of the shear band is compared to the orientation of an existing slip surface inside the clayey gouge and this result is used to deduce the orientation of the principal stresses. It is shown that as commonly observed in weak fault zones, the orientation of the principal stresses is locally almost parallel and perpendicular to the fault axis.

Distributional Characteristics of Plant in Northern Region on Gyeonggi-Province

This study was to establish the floristic composition of northern region in Gyeonggi-Province area(126˚ 45' - 127˚ 37' E, 37˚ 31' - 38˚ 17' N). This work was investigated from April, 1988 to October, 2004. The flora of vascular plants of northern region in Gyeonggi-Province were consisted of total 2,030 taxa; 145 families, 656 genera, 1,611 species, 7 subspecies, 320 varieties, 1 subvarieties and 91 formae. Among them, Korean endemic species were composed of 46 families, 85 genera, 84 species, 35 varieties, 1 subvarieties, and 18 formae, total 138 taxa. The rare and endangered plants based on floral region indicated by Ministry of Environment were 416 taxa; V rank species 18 taxa, IV rank species 79 taxa, Ⅲ rank species 111 taxa, Ⅱ rank species 80 taxa, Ⅰrank species 128 taxa. Also the naturalized plants were 114 species, correspond to 39.7% of among total 287 species appeared in South Korea. the result of PCA, Gwangju mountain chain at northern region of Gyeonggi-Province has rich and diverse vascular plants, and there are many Korean endemic, rare and endangered plants. therefore Gwangju mountain chain must be the core axis in for conserving the plant biodiversity and richness.

1934 高速噴流拡散火炎の挙動における数値シミュレーション(G06-7 燃焼(3),G06 熱工学)

Assuming that flow velocity becomes faster, necking phenomenon occurs in the hydrogen diffusion flame which is watched with interest as the clean fuel. Upper stream from a necking part is laminar flow, and down stream from a necking part is turbulent flow. It is simulated by the CFD software Phoenics. In this study, a necking phenomenon was not observed in a laminar flow model and turbulence flow model analysis. However, necking phenomena observed in the analysis which assuming upper stream in the flame as laminar flow and other place as turbulent flow. The results obtained are as follows. Radius velocity toward axis increases in downstream from border below a laminar flow and turbulent flow. And flame surface moves to a core axis direction. Velocity to a center axis direction decreases in downstream from that. And flame surface spread.

A new global PKP data set to study Earth's core and deep mantle

We present an extension of the previously developed algorithm for Simulated Annealing Waveform Inversion of Body waves (SAWIB) to resolve the interference between direct PKP seismic phases and their corresponding depth phases (pPKP and sPKP) which occurs for shallow earthquakes. This allows us to process shallow earthquakes previously discarded by the analysts, and therefore improve spatial sampling of the deep Earth by PKP phases. The SAWIB algorithm is applied to available waveform data to determine PKP travel times and amplitudes. The new data set of PKP travel times and amplitudes is significantly larger than previous ones. PKP (bc–df) differential travel time residuals display a hemispherical pattern in the inner core when plotted as a function of the angle between PKPdf propagation direction in the inner core and Earth's rotation axis. Most anomalous differential travel times are along polar paths in the quasi-western hemisphere (180 °W–40 °E), corresponding to earthquakes in the South Sandwich Islands recorded at northern seismic stations. PKP (ab–df) differential travel times display a larger scatter, which we attribute to heterogeneities at the base of the mantle. Relative amplitudes and t * attenuation parameters are analyzed in terms of inner core attenuation. The inner core attenuation decreases with increasing depth. In the upper inner core, in the depth range 150–220 km, an hemispherical pattern appears with a quasi-western hemisphere (40 °E–180 °E) faster and more attenuating than the rest of the inner core. When stacking PKP waveforms deconvolved by their source time function, we do not find evidence of a global innermost inner core velocity discontinuity. However we cannot rule out the existence of strong local heterogeneities or radial anisotropy variations from our data.

Erratum: "Sub-Milliarcsecond Imaging of Quasars and Active Galactic Nuclei. IV. Fine-Scale Structure" ([URL ADDRESS="/cgi-bin/resolve?2005AJ....130.2473K" STATUS="OKAY"]AJ, 130, 2473 [2005][/URL

The limit flag on theminor core axis FWHM, min, was incorrectly shown as ‘‘>’’ in themachine-readable version of Table 2, position 51. It should be ‘‘<,’’ indicating an upper limit of min for all the cases in which the limit is defined. The printed version and HTML version of Table 2 are correct as published. This correction of the machine-readable version of Table 2 is only typographical in nature, and none of the results in the paper were affected. Online material: machine-readable table

Maturation of phage T7 involves structural modification of both shell and inner core components

The double-stranded DNA bacteriophages are good model systems to understand basic biological processes such as the macromolecular interactions that take place during the virus assembly and maturation, or the behavior of molecular motors that function during the DNA packaging process. Using cryoelectron microscopy and single-particle methodology, we have determined the structures of two phage T7 assemblies produced during its morphogenetic process, the DNA-free prohead and the mature virion. The first structure reveals a complex assembly in the interior of the capsid, which involves the scaffolding, and the core complex, which plays an important role in DNA packaging and is located in one of the phage vertices. The reconstruction of the mature virion reveals important changes in the shell, now much larger and thinner, the disappearance of the scaffolding structure, and important rearrangements of the core complex, which now protrudes the shell and interacts with the tail. Some of these changes must originate by the pressure exerted by the DNA in the interior of the head.

Observations of the near-field structures of the glottal flow

The three-dimensional glottal jet was measured downstream from a self-oscillating physical model of the vocal folds using several techniques, including grid-based hotwire anemometry, high-speed flow visualization, and particle image velocimetry. Coherent flow structures were extracted from the spatio-temporal data using principal component analysis (PCA). The glottal jet resembled planar jets through static slitlike orifices. The direction of the jet core axis oscillated in the medial-lateral direction. Also, there was a positive correlation between the dynamics of shear layers around the laminar jet core and flow structures in the transitional region. This finding was similar to the dynamics of planar jets where jet flapping was observed previously. This can be understood in terms of an antisymmetric array of large-scale vortices being convected downstream. This antisymmetric mode of coherent vortex structures acts as an acoustic dipole that could effect the dynamics of the shear layers in the laminar core region. Thus, our observations help to understand the dynamics of the acoustic near-field of the glottal oscillator and suggest a possible feedback mechanism for source-tract coupling.

Thermal and Fragmentation Properties of Star‐forming Clouds in Low‐Metallicity Environments

The thermal and chemical evolution of star-forming clouds is studied for different gas metallicities, Z, using the model of Omukai, updated to include deuterium chemistry and the effects of cosmic microwave background (CMB) radiation. HD-line cooling dominates the thermal balance of clouds when Z ~ 10-5 to 10-3 Z☉ and density ≈105 cm-3. Early on, CMB radiation prevents the gas temperature from falling below TCMB, although this hardly alters the cloud thermal evolution in low-metallicity gas. From the derived temperature evolution, we assess cloud/core fragmentation as a function of metallicity from linear perturbation theory, which requires that the core elongation ≡ (b - a)/a > NL ~ 1, where a (b) is the short (long) core axis length. The fragment mass is given by the thermal Jeans mass at = NL. Given these assumptions and the initial (Gaussian) distribution of , we compute the fragment mass distribution as a function of metallicity. We find that (1) for Z = 0, all fragments are very massive, 103 M☉, consistent with previous studies; (2) for Z > 10-6 Z☉ a few clumps go through an additional high-density (1010 cm-3) fragmentation phase driven by dust cooling, leading to low-mass fragments; (3) the mass fraction in low-mass fragments is initially very small, but at Z ~ 10-5 Z☉ it becomes dominant and continues to grow as Z is increased; (4) as a result of the two fragmentation modes, a bimodal mass distribution emerges in 0.01 < Z/Z☉ < 0.1; and (5) for 0.1 Z☉, the two peaks merge into a single-peaked mass function, which might be regarded as the precursor of the ordinary Salpeter-like initial mass function.

Application of candle burnup strategy for future nuclear energy utilization

The CANDLE burnup strategy is a new reactor burnup concept, where the distributions of fuel nuclide densities, neutron flux, and power density move with the same constant speed along the core axis from bottom to top (or from top to bottom) of the core and without any change in their shapes. Therefore, any burnup control mechanisms are not required, and reactor characteristics do not change along burnup. The reactor is simple and safe. If this burnup scheme is applied to some neutron rich fast reactors, either natural or depleted uranium can be utilized as fresh fuel after second core and the burnup of discharged fuel is about 40%. It means about 40% of natural or depleted uranium can be utilized without either enrichment or reprocessing. In the ideal nuclear energy utilization system, the radioactive toxicity in the environment should remain or decrease after the utilization. This requirement is very severe and difficult to be satisfied. It may take too much time for its realization. The CANDLE burnup may substitute this period. Though it is a once-through fuel cycle, the discharged fuel burnup is about ten times of the present value for light water reactors. The space necessary for final disposal can be drastically reduced. However, in order to realize such a high burnup of discharged fuels some innovative technologies should be developed. Either new material standing still for such a high burnup or intermediate recladding will be required. Especially new fuel development will take a lot of time. For the time being a small reactor with CANDLE burnup may be a good option for nuclear power generation. Even this kind of reactor requires some innovative technologies and a long period for their developments. For the first stage of CANDLE burnup the prismatic fuel high-temperature gas cooled reactor is preferable. Since the design of this reactor fits to the CANDLE burnup very well, only a little time is required for its research and development.

Simulation study on candle burnup applied to block-type high temperature gas cooled reactor

The CANDLE burnup is a new reactor burnup concept, where the distributions of fuel nuclide densities, neutron flux, and power density move with the same constant speed along the core axis from bottom to top (or from top to bottom) of the core and without any change in their shapes. It can be applied easily to a block-type high temperature gas cooled reactor (HTGR) using an appropriate burnable poison with a high neutron absorption cross section mixed with uranium oxide fuel. In this study, natural gadolinium is used as burnable poison. In the present paper, the simulation of the burnup for the steady state and the startup is performed. For the steady state simulation with direct solutions of steady state nuclide densities as inputs, the difference between the results of the steady state analysis and the simulation analysis is very small. It confirms that the steady state analysis is correct. When the initial core is constructed from easily available nuclides, the simulation result gives a reactivity change of 1.7% at a burnup time of 0.7 years.

Interpretation of small-angle scattering data of inhomogeneous ellipsoids

Small-angle scattering data of inhomogeneous ellipsoidal particles are discussed in terms of their pair distance distribution functionsp(r). Special attention is given to the determination of core and shell thicknesses and axis ratios as well as to large distances within the particles, since cross terms between parts of positive and negative contrast within the particle can produce misleading results, similar to homogeneous particles or Janus particles. Cross-section pair distance distribution functionspc(r) of cylinders with elliptical cross sections show similar behaviour. Theoretical calculations are compared with small-angle X-ray and neutron scattering (SAXS and SANS) data of cetyltrimethylammonium bromide in aqueous KCl solutions.

Core-mantle relative motion and coupling

Core motion induced by lunisolar precession of the mantle is analysed and compared with experiments and Earth observations. First-order motion has the core axis lagging the mantle axis in precession by a small angle. This misalignment of the axes results in core-mantle relative velocities and displacements over the core-mantle interface as second-order flow. A third-order flow seen in experiments consists of nested fluid cylinders concentric with the core axis. First-order motion can be compared with westward drift and energy dissipation. Second-order motion can be compared with Earth observations using geomagnetic data, although its complexity may require numerical studies for detailed analysis. A specific lag angle and corresponding surface motions are suggested for comparison with Earth data leading to an apparent need for magnetic coupling between the core and the mantle.

Resonant Ultrasound Spectroscopy: theory and application

SUMMARY Resonant Ultrasound Spectroscopy (RUS) uses normal modes of elastic bodies to infer material properties such as elastic moduli and Q. In principle, the complete elastic tensor can be inferred from a single measurement. For centimeter-sized samples RUS fills an experimental gap between low-frequency stress-strain methods (quasi-static up to a few kHz) and ultrasonic time-delay methods (hundreds of kHz to GHz). We use synchronous detection methods to measure the resonance spectra of homogeneous rock samples. These spectra are then fit interactively with a model to extract the normal-mode frequencies and Q factors. Inversion is performed by fitting the normal-mode frequencies. We have successfully applied this technique to a variety of isotropic and anisotropic samples, both man-made and natural. In this paper we will show in detail the procedure applied to a cylindrical core of Elberton granite. By means of a statistical fit of the measured normal modes and an independent laser ultrasonic measurement, the granite core was inferred to have orthorhombic symmetry. A 10 per cent P-wave anisotropy was measured in the plane perpendicular to the core axis.

A new method for obtaining and quantifying the reliability of structural data from axially-oriented drill core using a fabric of known orientation

A new method for obtaining structural data from drill cores using a reference fabric (e.g. cleavage) to re-orient the core is presented (minimum-discordance method). Where the plunge and azimuth of the core is known, the most likely orientation of the core is taken to be the position in which the angle between the cleavage (in core) and its assumed regional orientation is at a minimum. In this position the pole to the cleavage (in core) lies in the plane defined by the drill hole axis and the reference orientation of the pole to the cleavage. With the most likely orientation of the core fixed, the orientation of other structural elements may be determined. Statistical analysis (Monte Carlo simulation) is used to assess factors affecting the reliability of the minimum-discordance method. Acceptable results (>70% probability solutions for fabrics of unknown orientation are within 15° of their correct orientation) are obtained where: (i) the standard deviation in the orientation of the reference fabric is less than 15° (1 σ), (ii) the reference fabric is inclined at 20–60° to the core axis, and (iii) either the pole to the plane or the lineation whose orientation is originally unknown is at <45° to the core axis. Best results are obtained where the reference plane is at ∼30° to the core axis. A previously published method that uses only the average strike of the reference fabric to determine the orientation of the core is shown to have additional geometric restrictions that render results unreliable in many situations. Ideally, estimates of the average orientation and variability of the reference fabric are based on field data. However, for surveyed drill holes of widely ranging orientation, the minimum-discordance method can be used to determine the average orientation and minimum degree of scatter for the reference fabric directly from the core. We demonstrate this, and the applicability of our method, with an example from Lewis Ponds, New South Wales.

Single-electron states near a current-carrying core

The energy spectrum of an electron confined near a current-carrying core is obtained as a function of the azimuthal applied magnetic field within the effective-mass approximation. The double degeneracy of the non-zero electron's axial wave number ( k z ) states is lifted by the current-induced magnetic field while that of the non-zero azimuthal quantum number ( m) states is preserved. A further analysis is the evaluations of the oscillator strengths for optical transitions involving the lowest-order pair of the electron's energy subbands within the dipole approximation. The radiation field is taken as that of elliptically polarized light incident along the core axis. In this polarization and within the dipole approximation, the allowed transitions are only those governed by the following specific selection rules. The azimuthal quantum numbers of the initial and final states must differ by unity while the electron's axial wave number is conserved. The azimuthal magnetic field is also found to lift the multiple degeneracies of the k z ≠0 interaction integrals as well as those of the oscillator strengths for optical transitions.

Measurement of fold axes in drill core

Measuring the orientation of fold axes is a routine component of field-based structural analysis. Determining the real-space orientations of small-scale folds in drill cores, however, remains a time consuming and often cumbersome task unless the fold axis lies on an exposed plane. We present a method for accurately determining the orientation of fold axes that do not lie on exposed planes in drill core, provided the core is oriented or can be reoriented using the assumed orientation of one of the fabrics within it. Two angles that uniquely specify the orientation of the fold axis with respect to the core are measured. One is the angle between the fold axis and the core axis. The other, measured in a plane perpendicular to core axis, couples the orientation of the fold axis to either a core orientation mark or another fabric of known orientation. The real-space orientation of the fold axis can either be calculated from the two measured angles and the plunge and azimuth of the drill hole or determined using a simple stereonet construction. Measurements are made with respect to the two points of intersection between the fold axis and the outer surface of the core. While this means the technique is best suited for use with a whole core, it has the advantage that fold axes need not lie on exposed planes in the core.

The in situ stress states associated with core discing estimated by analysis of principal tensile stress

Abstract Core discing occurs due to tensile stress induced by boring within or below a core stub when the minimum principal stress is nearly in the same direction as the core axis. To determine the effects of the core length on the magnitude and direction of tensile principal stress, a finite element analysis was carried out for an HQ core of different lengths for 77 in situ stress conditions. According to the minimum value and the mean inclination relative to the core axis for ‘the maximum semi-axial tensile stresses’, 30 in situ stress conditions were identified as being stress conditions under which core discing is likely to occur, and conditions necessary for in situ stress were proposed. The critical tensile stress, which is the tensile stress that can produce a tensile fracture that propagates throughout a cross-section, was analyzed for these stress conditions and a new criterion for core discing, which can be applied to a core of any length, was proposed. The stress conditions estimated by the criterion were consistent with previous experimental results for a long core and for thin discs. According to the criterion, the relationship between the core length and the in situ stress necessary for core discing was examined. Our analysis showed that the stress field can be divided into three regions and that core discing of short length mostly occurs at great depth. The average relationship between the core length and the disc thickness was determined by assuming that the position of a fracture is given by the mean position of ‘the maximum semi-axial tensile stresses’. Our theoretical estimates reproduced previous experimental results regarding the effects of stress magnitude on the thickness of the disc. Thus, the present proposed criterion can be used to estimate the stress condition for core discing with a given disc thickness.

Permeability of the rocks from the Kola superdeep borehole at high temperature and pressure: implication to fluid dynamics in the continental crust

Permeability of the samples collected from the surface and from the depths of 8–11 km in the Kola SG-3 and from the depth of 3.8 in the KTB boreholes was studied at temperatures up to 600 °C and pressures up to 150 MPa. These PT correspond to in situ conditions of the deep parts of the superdeep boreholes and to the conditions of progressive and regressive metamorphism of the Kola series rocks. The experiments were carried out with fluid filtration parallel and normal to rock foliation and parallel to core axis. The temperature–permeability trend behavior depends on effective pressure and depth of sample collection. At low effective pressure, a temperature increase leads first to a permeability decrease and then to its increase. At higher effective pressure, inversions appear on all the temperature trends of the samples collected from great depths. In contrast, permeability of the samples selected at shallow depth (3.8 km) and on the surface decreases within the entire temperature range. As a rule, with flow parallel to foliation, the values of permeability are higher than with flow normal to foliation. The results of microstructure studies allow to conclude that microcrack initiation and closure, due to a competitive influence of temperature and pressure cause such permeability behavior. In the samples, there are two families of microcracks: with low aspect ratio and those with high aspect ratio. Their effect on rock permeability changes with temperature. On sample heating, the low aspect ratio microcracks close and, on the contrary, high aspect ratio ones open. The total effect is expressed by minima in the temperature–permeability trends. Permeability anisotropy increases with temperature, reaches a maximum at 200 °C and then decreases. Sample permeability decreases with different gradients at simultaneous increase of temperature and pressure, simulating in situ depth increase. Hence, the deep seat rocks can vary greatly in permeability and against the common background of permeability decrease with depth, local deep aquifers may occur. At PT of progressive metamorphism the permeability values were high enough to permit the fluid flow to penetrate the whole volume of rock massif. At PT of regressive metamorphism, the permeability values were a few decimal orders lower, so fluid flow could be concentrated in large disjunctive zones only.

POND: an Excel spreadsheet to obtain structural attitudes of planes from oriented drillcore

The Planes from Oriented and Navigated Drillcore (POND) Excel ® spreadsheet allows determination and presentation of the attitudes of planes intersected in ‘oriented’ and ‘navigated’ diamond drillcore. Two drillcore navigation measurements (azimuth and plunge from a deviation log), and two plane-to-drillcore angular measurements (angle to core axis, and angle between orientation mark and intersection ellipse) are required to obtain a solution. All possible drillcore orientations are supported and multiple plane orientations can be determined simultaneously. Graphical results are presented on a stereonet as poles to the intersected planes. Numerical results are presented in a matrix to allow clipping into stereonet programs for contouring and more formal and involved structural analysis and display.