Principal Orientations Research Articles

KDP/DKDP倍频晶体主截面定位方法

KDP/DKDP倍频晶体主截面定位方法

Discriminative sparsity graph embedding based on histogram of rotated princial orientation gradients

The unconstrained face images collected in the real environments include many complicated and changeable interference factors, and sparsity preserving projections (SPP) cannot well obtain the low-dimensional intrinsic structure embedded in the high-dimensional samples, which is important for subsequent sparse representation classifier (SRC). To deal with this problem, in this paper we propose a new method named discriminative sparsity graph embedding based on histogram of rotated principal orientation gradients (DSGE-HRPOG). Firstly, it extracts multi-scale and multi-directional gradient features of unconstrained face images by HRPOG feature descriptor and incorporates them into a discriminative feature dictionary of sparse representation classifier. Secondly, it seeks an optimal subspace of HRPOG feature dictionary in which the atoms in intra-classes are as compact as possible, while the atoms in inter-classes are as separable as possible by adopting the proposed DSGE dimensionality reduction method. Finally, an optimal algorithm is presented in which the low-dimensional projection and the sparse graph construction are iteratively updated, and the accuracy of unconstrained face recognition is further improved. Extensive experimental results on AR, Extended Yale B, LFW and PubFig databases demonstrate the effectiveness of our proposed method.

Comparison of REV size and tensor characteristics for the electrical and hydraulic conductivities in fractured rock

The representative elementary volume (REV) is a critically important concept in fractured rock investigations as it tells us at what scale the fractured domain can be represented by an anisotropic tensor as opposed to requiring the details of each individual fracture for modelling purposes. Whereas the REV size and corresponding tensor characteristics for the hydraulic conductivity (K) in fractured rock have been the subject of numerous previous investigations, no studies to date have focused on the electrical conductivity (σ). This is despite the fact that geoelectrical measurements are arguably the most popular means of geophysically investigating fractured rock, typically via azimuthal resistivity surveying where the observed electrical anisotropy is commonly used to infer hydraulic characteristics. In this paper, we attempt to fill this void and present a systematic numerical study of the impacts of changes in fracture-network properties on the REV size and equivalent tensor characteristics for both the electrical and hydraulic conductivities. We employ a combined statistical and numerical approach where the size of the REV is estimated from the conductivity variability observed across multiple stochastic fracture-network realizations for various domain sizes. Two important differences between fluid and electric current flow in fractured media are found to lead to significant differences in the REV size and tensor characteristics for σ and K; these are the greater importance of the matrix in the electrical case and the single power instead of cubic dependence of electric current flow upon aperture. Specifically, the REV for the electrical conductivity will always be smaller than that for the hydraulic conductivity, and the corresponding equivalent tensor will exhibit less anisotropy, often with notably different principal orientations. These findings are of key importance for the eventual interpretation of geoelectrical measurements in fractured rock, where we conclude that extreme caution must be taken when attempting to make the link to hydraulic properties.

Contemporary crustal stress of the Greek region deduced from earthquake focal mechanisms

A massive dataset of over 1900 focal mechanisms of crustal earthquakes with M ≥ 3.5 in the Greek region was employed to resolve the contemporary stress-field using a damped least-squares inversion. The results are in good agreement with the strain-rate field of the Global Strain Rate Model, which was used as reference, both in terms of their principal axes orientations and expected faulting styles. Dual stress-states were identified using the Multiple Inverse Method in regions delineated by joining neighboring Area Sources of the European Seismic Hazard Model 2013 (ESHM13). North-western Greece is mostly affected by transpressional tectonics characterized by NE-SW contraction. Northern/central Greece and the Corinth Rift are dominated by E-W normal faulting, with secondary oblique-normal to strike-slip faulting at the western margin of the latter. North and central Aegean are mainly governed by transtensional regime, characterized by stable N-S extension.The stress-tensor was found to be compatible with the Fault Sources (FS) of ESHM13, in terms of orientation and expected faulting type. Differences were observed in regions of low strain-rate, such as the Southern Aegean, where left-lateral, E-W strike-slip instead of normal faulting was inferred. Discrepancies in areas with strong local heterogeneities were highlighted by anomalies in the stress-ratio, Φ, indicating transtensional regime in the pull-apart basins of Western Greece and transpressional tectonics in north-western Greece and south of Crete. The latter is characterized by stable N-S contraction, SW-NE sinistral strike-slip and E-W reverse faulting in the vicinity of the subduction zone. A low Φ, E-W oriented zone was identified along the active volcanic arc, where a remarkable 90° rotation occurs in the stress field. This rotation is related to the transition from E-W (in the north) to N-S (in the south) normal faulting in Peloponnese and Dodecanese Islands, as well as rearrangement from dextral to sinistral SW-NE strike-slip faulting in North and South Aegean, respectively.

Heterogeneities in Stress and Strength in Tohoku and Its Relationship with Earthquake Sequences Triggered by the 2011 M9 Tohoku-Oki Earthquake

Inland Tohoku has been recognized as under the WNW-ESE compressional stress state before the 2011 M9 Tohoku-Oki earthquake. Earthquakes that occurred there were characterized by reverse faulting with the compressional axis oriented in almost the WNW-ESE direction. The Tohoku-Oki earthquake reduced this WNW-ESE compressional stress and, therefore, should have suppressed the earthquake occurrence. However, several intensive earthquake sequences were triggered in inland Tohoku. In this study, we investigated the triggering mechanism of these remote earthquake sequences in the stress shadow based on the detailed distribution of stress orientations newly determined from pre-mainshock focal mechanism data. The spatial distribution of stress orientations shows that there exist some regions with anomalous stress fields even before the Tohoku-Oki earthquake on the spatial scale of a few tens of kilometers. This spatial heterogeneity in the stress field suggests that the differential stress magnitude in inland Tohoku is low (a few tens of MPa). Locations of the earthquake clusters tend to correspond to regions where the principal stress axis orientations of the pre-mainshock period are similar to those of the static stress change by the Tohoku-Oki earthquake. This observation suggests that these earthquake sequences were triggered by a local increase in differential stress due to the static stress change. However, a few swarm sequences occurred in central Tohoku with delays ranging from a few days to few weeks after the Tohoku-Oki earthquake despite the reduction in differential stress. These sequences have notable characteristics including upward migration of hypocenters. Such features are similar to the fluid-injection induced seismicity. The source regions of these swarms are located near the ancient caldera structures and major geological boundaries. The swarm activities were probably triggered by the upward fluid movement along such pre-existing structures. These observations demonstrate that information about the temporal evolutions of both stress and frictional strength is necessary to understand the triggering mechanism of earthquakes.

A dynamic model of polyethylene damage in dry total hip arthroplasties: wear and creep

The creep and wear of ultra-high-weight polyethylene hip prostheses under physiological conditions are studied in the present research work. A fully integrated contact-coupled dynamic model based upon multibody dynamics methodology is developed, allowing the evaluation of not only sliding distance, but also contact mechanics as well as cross-shear effects and both average pressure and in-service duration associated with the creep phenomenon. In vivo forces and motions of hip joint are used as input for the dynamic simulation, which result in more realistic contact point trajectory and contact pressure, and consequently wear and creep, compared to simplified inputs. The analysis also takes into account inertia forces due to hip motion, tribological properties of bearing bodies, and energy loss owing to contact-impact events. The principal molecular orientation (PMO) of the polyethylene cup is determined through an iterative algorithm and dynamic outcomes. Archard’s wear law is also integrated into the multibody dynamics model for wear prediction in hip implants. Creep, besides wear, is attributed to polyethylene damage, which is investigated by implementing a creep model extracted from experimental data. The model is validated using clinical data and numerical results available from previously published studies. It is shown that creep plays a significant role in hip damage along with wear, both of which can be influenced by hip parameters, e.g., hip and clearance sizes. Moreover, the creep mechanism according to creep experiment is discussed, and contributing factors to the wear phenomenon are analyzed throughout this study.

Antropología médica en América Latina 1990-2015: Una revisión estrictamente provisional

The article presents a provisional examination of the production of Latin American medical anthropology, especially from Mexico, and to a lesser degree Brazil, from 1990 to 2015, in an attempt to highlight the discipline's principal contributions, orientations and objectives, but also to pose critiques and doubts, especially with respect to the omission of the study of serious collective health problems and processes. The article attempts to put into evidence the importance of the discipline not only for anthropology, but also for biomedicine, suggesting the need for complementation beyond the differences and incompatibilities that exist regarding, for example, the use of qualitative techniques, and interventions -or lack of interventions- regarding the customs of the different social actors with respect to health/disease/care-prevention processes.

Fracture Properties of Nash Point Shale as a Function of Orientation to Bedding

AbstractUnderstanding how fracture networks develop in shale formations is important when exploiting unconventional hydrocarbon reservoirs and analyzing the integrity of the seals of conventional and carbon capture and storage reservoirs. Despite this importance, experimentally derived fracture data for shale remains sparse. Here we characterize shale from Nash Point in South Wales, United Kingdom, in terms of ultrasonic wave velocities, tensile strength, and fracture toughness (KIc). We measure these properties in multiple orientations, including angles oblique to the three principal fracture orientations—Short‐transverse, Arrester, and Divider. We find that the Nash Point shale is mechanically highly anisotropic, with tensile strength and KIc values lowest in the Short‐transverse orientation and highest in the Arrester and Divider orientations. Fractures that propagate in a direction oblique or normal to bedding commonly deflect toward the weaker Short‐transverse orientation. Such deflected fractures can no longer be considered to propagate in pure mode‐I. We therefore present a method to correct measured KIc values to account for deflection by calculating mode‐I and mode‐II deflection stress intensities (KId and KIId, respectively). Because of the mixed‐mode nature of deflected fractures, we adopt a fracture (Gc) energy‐based approach that allows analysis of critical fracture propagation conditions for both deflected and undeflected fractures in all orientations. We find that Gc increases as the angle from the Short‐transverse plane increases. We conclude that a modified elliptical function, previously applied to tensile strength and KIc, can be used to estimate values of Gc at angles between the Short‐transverse and Arrester orientations.

Learning principal orientations and residual descriptor for action recognition

In this paper, we propose an unsupervised representation method to learn principal orientations and residual descriptor (PORD) for action recognition. Our PORD aims to learn the statistic principal orientations and to represent the local features of action videos with residual values. The existing hand-crafted feature based methods require high prior knowledge and lack of the ability to represent the distribution of features of the dataset. Most of the deep learned feature based methods are data adaptive, but they do not consider the projection orientations of features nor the loss of locally aggregated descriptors of the quantization. We propose a method of principal orientations and residual descriptor considering that the principal orientations reflect the distribution of local features in the dataset and the residual of projection contains discriminative information of local features. Moreover, we propose a multi-modality PORD method by reducing the modality gap of the RGB channels and the depth channel at the feature level to make our method applicable to RGB-D action recognition. To evaluate the performance, we conduct experiments on five challenging action datasets: Hollywood2, UCF101, HMDB51, MSRDaily, and MSR-Pair. The results show that our method is competitive with the state-of-the-art methods.

Precambrian basement reservoirs: Case study from the northern Bongor Basin, the Republic of Chad

Bongor Basin in the south of Chad is a Cretaceous–Paleogene rift basin developed on Precambrian crystalline basement and is part of the central African rift system (CARS). High oil flows have been tested from five basement buried hills, indicating that the Precambrian basement is a good reservoir for hydrocarbon accumulation. Core analyses from 10 wells indicate that the basement rocks are composed of plutonic rocks (including granite, syenite, monzonite, quartz monzonite, and diorite) and orthometamorphites (including migmatitic granite, migmatitic gneiss, and granulite). Structural mapping of the top basement shows that faults in basement have a principal strike orientation of west–northwest-east–southeast and a secondary orientation of northeast–southwest. A combination of mud losses, well testing results, cores, wire-line logs, Formation MicroImager, sonic scanner logs, and three-dimensional seismic data were used to identify and detect the basement reservoirs. Two main sets of high-angle fractures, striking west–northwest-east–southeast and west–southwest-east–northeast, were identified. Three facies are divided based on the degree of weathering, intensity of fracturing, and sonic anisotropy. The basement can be divided vertically into four zones: weathered and leached, fractured, semifilled fractured, and tight zones. The weathered and leached and fractured zones are the main basement reservoirs in the study area. The effective porosities range from 3% to 10%, in places up to 25%. The porosity and permeability of basement reservoirs depend on the structural location and hydrothermal and authigenic precipitates developed during and after the basin formation. The discovery of basement reservoirs in the Bongor Basin will aid the hydrocarbon exploration of a new play in the CARS.

On the greenish-yellow color of natural Brazilian titanite

Natural greenish-yellow titanites from two localities in Brazil (Bananal/Capelinha, MG and Xambioa, TO) were characterized by electron paramagnetic resonance (EPR) and optical absorption. Along with vanadyl ions (VO2+) substituting Ti4+, two other paramagnetic centers were identified: the Fe3+ and the Mn2+. For the VO2+, the principal values and orientations of the g and A tensors were derived from a careful analysis of the angular dependence of the EPR spectra. The obtained results, although different to previously reported data, still support the model for the VO2+ bonds to the nearest oxygen (O1) in the TiO6-distorted octahedra. In addition, the titanite optical absorption spectra were analyzed, and the yellow color was ascribed to Fe3+ ↔ O2− ligand–metal charge transfer transitions (LMCT) in the near-ultraviolet, extending to the violet and blue spectral ranges. The VO2+ center seen by EPR was in low concentration and had no visible effect on the color. Finally, γ-irradiation up to 200 kGy and thermal treatments in oxidizing/reducing atmospheres up to 600–700 °C also had no big influence on the dominant yellow color.

Size Effect Analysis for the Characterization of Marcellus Shale Quasi-brittle Fracture Properties

Mechanical characterization of shale-like rocks requires understanding the scaling of the measured properties to enable the extrapolation from small scale laboratory tests to field study. In this paper, the size effect of Marcellus shale was analyzed, and the fracture properties were obtained through size effect tests. A number of fracture tests were conducted on Three-Point-Bending (TPB) specimens with increasing size. Test results show that the nominal strength decreases with increasing specimen size, and can be fitted well by Bazant's Size Effect Law (SEL). It is shown that SEL accounts for the effects of both specimen size and geometry, allowing an accurate identification of the initial fracture energy of the material, Gf, and the effective Fracture Process Zone (FPZ) length, cf. The obtained fracture properties were verified by the numerical simulations of the investigated specimens using standard Finite Element technique with cohesive model. Significant anisotropy was observed in the fracture properties determined in three principal notch orientations: arrester, divider, and short-transverse. The size effect of the measured structural strength and apparent fracture toughness was discussed. Neither strength-based criterion which neglects size effect, nor classic LEFM which does not account for the finiteness of the FPZ can predict the reported size effect data, and nonlinear fracture mechanics of the quasibrittle type is instead applicable.

Anisotropic elastic, strength, and fracture properties of Marcellus shale

Shales are considered to be both source and cap rocks, and play an important role in various geotechnical applications including oil and gas exploration and production. A deep understanding of the mechanical properties of shale is essential. In this work, deformability, strength, and fracturability of Marcellus shale were investigated through experimental studies, and a database of its mechanical properties was generated. Uniaxial compression, direct tension, and Brazilian tests were performed on Marcellus shale specimens in various bedding plane orientations with respect to loading directions to study the static mechanical properties of the material and their anisotropy. The experimental results revealed that the transversely isotropic model is applicable for describing the elastic behavior of Marcellus shale in pure tension and compression. However, the elastic properties measured from these two experiments were not exactly the same. In addition, differences exist between Brazilian and direct tensile strengths, both of which varied with bedding plane orientations and loading directions, and were associated with different failure modes. The deformability of Marcellus shale was also studied through seismic velocity measurements, as a means for comparison with the static measurements. Finally, a series of three-point-bending tests were conducted on specimens of increasing size in three different principal notch orientations to investigate the fracture properties of the material. It was found that there exists a significant size effect on the fracture properties calculated from the measured peak loads using Linear Elastic Fracture Mechanics (LEFM). The fracture properties of the material calculated by using Bažant's Size Effect Law (SEL) were independent of the testing method and were found to be anisotropic.

Surface impurities on giant gypsum crystals from “la Cueva de las Espadas” (Cave of Swords), Naica, Mexico

The Cave of Swords was discovered in 1910 at Naica, Chihuahua, Mexico. During the last century, human presence has changed the microclimate conditions inside this cave, raising the question of whether anthropogenic action resulted in the deterioration of its gypsum single crystals and in the deposition of impurities on their surfaces. The present work provides a detailed characterization of representative samples of this cave and suggests an answer to the origin of the impurities on the surface of these nature-made large crystals. Laboratory and synchrotron characterization techniques are applied. For the first time, the samples single-crystal nature and the fragmentation effect of impurities are characterized. Synchrotron light diffraction measurements performed on a collection of characteristic samples consistently reveal sharp textures, with crystal reciprocal vectors [0,1,0] preferably perpendicular to the samples principal cleavage planes and orientation widths averaging 8°. X-ray diffraction identifies galena, sphalerite, hematite, goethite and cuprite on the crystals’ surface. Diffraction results indicate no correlation between the number of phases of impurities present and crystallinity. Micro X-ray fluorescence clarifies the elemental spatial distribution. The correlations between the elemental distributions confirm the phase identification obtained by diffraction. For Mn and Pb, the correlations point to the presence of amorphous oxides. Minor phases’ characterization suggests they have been deposited on iron oxy-hydroxide substrates. All the identified phases correspond to minerals that were abundantly present in Naica ore deposit before any anthropogenic activity. The impurities on the surface of gypsum crystals at the Cave of Swords were not produced by human presence.

Detection of deformation anisotropy of tuff by a single triaxial test on a single specimen

Rock anisotropy has conventionally been determined by numerous tests using many specimens sampled at several orientations, however, it is both costly and time consuming. The anisotropic deformation properties (transversely isotropic elasticity and its dominant orientation) of a tuffaceous rock sample obtained in Utsunomiya city, Japan, and characterized by a clear bedding plane, were determined by a newly proposed method, namely, a single triaxial test using a single specimen. Using this method, the dominant orientations of anisotropy are determined by the principal orientations of the strain during isotropic consolidation, and the elastic parameters can be determined by stresses and strains during triaxial compression. This method required the implementation of a triaxial testing apparatus with a newly designed cap including a slider mechanism and low-friction sheets. The six components of the symmetrical, small strain tensors of the tuff specimen were measured using nine strain gauges, while the 3D principal strains were evaluated during uniaxial and consolidated drained triaxial tests. To verify the proposed method, the anisotropic properties of four specimens sampled from a cubic block at different orientations, as characterized by the proposed method, were compared with those determined by multiple uniaxial tests using the specimens sampled for different orientations. The strain responses of the uniaxial tests demonstrated that the Young's modulus of the tuff in the bedding orientation is 1.5 times greater than that for the perpendicular orientation. The orientation of the principal strains deviate from the loading orientation due to the orientation of the bedding plane, and the orientations during isotropic consolidation were inclined in accordance with the dip orientation of the bedding plane. Similar values were evaluated for each anisotropic property determined by both a single triaxial test on each specimen and multiple uniaxial tests. The obtained values demonstrated that the Young's moduli for the bedding orientation are 1.5–2.7 times larger than that in the perpendicular orientation.

Region-specific constitutive modeling of the plantar soft tissue.

Recent research has shown that hyperelastic properties of the plantar soft tissue consisting of adipose tissue and fibrous septa change from region to region. However, relatively little research has been conducted to develop analytical or computational models to describe the region-specific behavior of the plantar soft tissue. The objective of the research is to develop a region-specific constitutive model of the plantar soft tissue. Plantar soft tissue specimens were dissected from six regions [subcalcaneal (CA), sublateral (LA), subnavicular (Nav), 1st, 3rd, and 5th submetatarsal (M1, M3, M5)] from cadaveric foot samples, and a picrosirius red staining technique was used to visualize the collagen fibers in fibrous septa. The volume fractions of adipose tissue and fibrous septa and the volume fractions of the principal orientations of the fibrous septa were calculated with the intensity gradient method. Region-specific constitutive models were then developed in finite element analysis considering the microstructure of the plantar soft tissue. The hyperelastic region specific material properties of the plantar soft tissue were validated with experimental unconfined compression tests and indentation tests from the literature. The results show that the models give reasonable predictions of the stiffness of the soft tissue within a standard deviation of the tests. The region-specific constitutive models help to explain how changes in the constituents are related to mechanical behavior of the soft tissue on a region specific basis.

A fast template matching algorithm based on principal orientation difference

In the case that the background scene is dense map regularization complex and the detected objects are low texture, the method of matching according to the feature points is not applicable. Usually, the template matching method is used. When training samples are insufficient, the template matching method gets a worse detection result. In order to resolve the problem stably in real time, we propose a fast template matching algorithm based on the principal orientation difference feature. The algorithm firstly obtains the edge direction information by comparing the images that are binary. Then, the template area is divided where the different features are extracted. Finally, the matching positions are searched around the template. Experiments on the videos whose speed is 30 frames/s show that our algorithm detects the low-texture objects in real time with a matching rate of 95%. Compared with other state-of-art methods, our proposed method reduces the training samples significantly and is more robust to the illumination changes.

Laser Conoscopy Study of Optical Anomalies in Uniaxial Crystals

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Contemporary Crustal Deformation Within the Pamir Plateau Constrained by Geodetic Observations and Focal Mechanism Solutions

We used an updated data set of 192 GPS-derived surface velocities and 393 earthquake focal mechanisms (Mw > 3.0, hypocenter depths < 30 km) to evaluate the spatial variations in the surface strain rate and crustal stress regime throughout the Pamir Plateau and its surrounding regions. The strain rate field was estimated using the spline in tension approach that solves for the surface velocity in a rectangular grid and the stress field was predicted from focal mechanism solutions using the damped regional-scale stress inversion (DRSSI) method of Hardebeck and Michael (Journal of Geophysical Research, https://doi.org/10.1029/2005jb004144 , 2006). The results show that the crustal stress field around the Pamir Plateau is predominantly characterized by NNW–SSE compression and E–W extension, which is consistent with the principal orientations of the two-dimensional surface strain rate tensor. This agreement supports the notion that the Pamir and southwestern Tien Shan are uniformly strained blocks. In particular, the fan-shaped rotational pattern between $${\text{Shmax}}$$ and the strain rate from the western Pamir to the Tajik Basin shows that the counterclockwise rotation of the $${\text{Shmax}}$$ orientation is associated with vertical deformation, which is consistent with the idea of Schurr et al. (Tectonics 33(8):2014TC003576, 2014) concerning the gravitational collapse and westward extrusion of the crust in the western Pamir. We propose that such a stress–strain pattern, dominated by NNW–ESE oriented compression and E–W trending extension, originated from a combination of the northward push of the Indian continent and the southward subduction of the Tien Shan.

Production and In-Plane Compression Mechanics of Alternatively Angled Layered Cross-Laminated Timber

Increasing awareness of sustainable building materials has led to interest in enhancing the structural performance of engineered wood products. This paper reports mechanical properties of cross-laminated timber (CLT) panels constructed with layers angled in an alternative configuration on a modified industrial CLT production line. Timber lamellae were adhesively bonded together in a single-step press procedure to form CLT panels. Transverse layers were laid at an angle of 45°, instead of the conventional 90° angle with respect to the longitudinal layers’ 0° angle. Tests were carried out on 20 five-layered CLT panels divided into two matched groups with either a 45° or a 90° configuration; an in-plane uniaxial compressive loading was applied in the principal orientation of the panels. These tests showed that the 45°-configured panels had a 30% higher compression stiffness and a 15% higher compression strength than the 90° configuration. The results also revealed that the 45°-configured CLT can be industrially produced without using more material than is required for conventional CLT 90° panels. In addition, the design possibility that the 45°-configured CLT can carry a given load while using less material also suggests that it is possible to use CLT in a wider range of structural applications.