Application of oblique photogrammetry technique in geological hazard identification and decision management

With the continuous development of the oblique photography technique, it has been used more and more widely in the field of geological disasters. It can quickly obtain the three-dimensional(3D) real scene model of dangerous mountainous areas under the premise of ensuring the safety of personnel while restoring the real geographic information as much as possible. However, geological disaster areas are often accompanied by many adverse factors such as cliffs and dense vegetation. Based on this, the paper introduced the flight line design of oblique photogrammetry, analyzed the multi-platform data fusion processing, studied the multi-period data dynamic evaluation technology and proposed the application methods of data acquisition, early warning, disaster assessment and decision management suitable for geological disaster identification through the analysis of actual cases, which will help geologists to plan and control geological work more scientifically and rationally, improve work efficiency and reduce the potential personnel safety hazards in the process of geological survey, to offer technical support to the application of oblique photogrammetry in geological disaster identification and decision making and provide the scientific basis for personal and property safety protection and later-stage geological disaster management in disaster areas.

Exploring mechanism of hidden,steep obliquely inclined bedding landslides using a 3DEC model:A case study of the Shanyang landslide in Shaanxi Province,China

Catastrophic geological disasters frequently occur on slopes with obliquely inclined bedding structures(also referred to as obliquely inclined bedding slopes),where the apparent dip sliding is not readily visible.This phenomenon has become a focal point in landslide research.Yet,there is a lack of studies on the failure modes and mechanisms of hidden,steep obliquely inclined bedding slopes.This study investigated the Shanyang landslide in Shaanxi Province,China.Using field investigations,laboratory tests of geotechnical parameters,and the 3DEC software,this study developed a numerical model of the landslide to analyze the failure process of such slopes.The findings indicate that the Shanyang landslide primarily crept along a weak interlayer under the action of gravity.The landslide,initially following a dip angle with the support of a stable inclined rock mass,shifted direction under the influence of argillization in the weak interlayer,moving towards the apparent dip angle.The slide resistance effect of the karstic dissolution zone was increasingly significant during this process,with lateral friction being the primary resistance force.A reduction in the lateral friction due to karstic dissolution made the apparent dip sliding characteristics of the Shanyang landslide more pronounced.Notably,deformations such as bending and uplift at the slope’s foot suggest that the main slide resistance shifts from lateral friction within the karstic dissolution zone to the slope foot’s resistance force,leading to the eventual buckling failure of the landslide.This study unveils a novel failure mode of apparent dip creep-buckling in the Shanyang landslide,highlighting the critical role of lateral friction from the karstic dissolution zone in its failure mechanism.These insights offer a valuable reference for mitigating risks and preventing disasters related to obliquely inclined bedding landslides.

Factors that influence the results of indirect decompression employing oblique lumbar interbody fusion

BACKGROUND Indirect decompression is one of the potential benefits of anterior reconstruction in patients with spinal stenosis.On the other hand,the reported rate of revision surgery after indirect decompression highlights the necessity of working out prediction models for the radiographic results of indirect decompression with assessing their clinical relevance.AIM To assess factors that influence radiographic and clinical results of the indirect decompression in patients with stenosis of the lumbar spine.METHODS This study is a single-center cross-sectional evaluation of 80 consecutive patients(17 males and 63 females)with lumbar spinal stenosis combined with the instability of the lumbar spinal segment.Patients underwent single level or bisegmental spinal instrumentation employing oblique lumbar interbody fusion(OLIF)with percutaneous pedicle screw fixation.Radiographic results of the indirect decompression were assessed using computerized tomography,while MacNab scale was used to assess clinical results.RESULTS After indirect decompression employing anterior reconstruction using OLIF,the statistically significant increase in the disc space height,vertebral canal square,right and left lateral canal depth were detected(Р<0.0001).The median(M)relative vertebral canal square increase came toМ=24.5%with 25%-75%quartile border(16.3%;33.3%)if indirect decompression was achieved by restoration of the segment height.In patients with the reduction of the upper vertebrae slip,the median of the relative increase in vertebral canal square accounted for 49.5%with 25%-75%quartile border(2.35;99.75).Six out of 80 patients(7.5%)presented with unsatisfactory results because of residual nerve root compression.The critical values for lateral recess depth and vertebral canal square that were associated with indirect decompression failure were 3 mm and 80 mm2 respectively.CONCLUSION Indirect decompression employing anterior reconstruction is achieved by the increase in disc height along the posterior boarder and reduction of the slipped vertebrae in patients with degenerative spondylolisthesis.Vertebral canal square below 80 mm2 and lateral recess depth less than 3 mm are associated with indirect decompression failures that require direct microsurgical decompression.

Control Effect of Botanical Pesticides against Ectropis oblique hmpulina and Empoasca pirisuga in Tea Plantation

[ Objective ] The paper was to study the effects of several botanical pesticides against two pests in tea plantation. [ Method] Using randomized block de- sign, different concentrations of botanical pesticides were sprayed during the young larvae periods of Ectropis oblique hmpulina Wehrli and peak periods of Empoasca pirisuga, the reduction rate of population and control effects were investigated after spraying for 1,3,7 and 10 d. [ Result] 5% rotenone EC 800 times had the best control effect against E. oblique hmpulina, and 0.5% veratridine soluble liquid 800 times had the best control effect against E. pirisuga. 0. 5% veratridine soluble liquid, 0.2% celangulin EC, 0.3% matrine water agent and 7.5% rotenone EC could be selected as the pesticides for the control of E. oblique hmpulina; 0. 5% veratridine soluble liquid, 0. 2% celangulin EC, 0.3% azadirachtin EC, 0.3% matrine water agent and 7.5% rotenone EC could be selected as the pesticides for the control of E. pirisuga, of which 0. 3% azadiraehtin EC 600 times showed the best durable effect against E. pirisuga with control effect of 100% after spraying for 7 d. [ Conclusion] The results provided basis for application of botanical pesticides in pests control in tea plantation.

Acoustic evaluation of cementing quality using obliquely incident ultrasonic signals

Ultrasonic cement bond logging is a widely used method for evaluating cementing quality. Conventional ultrasonic cement bond logging uses vertical incidence and cannot accurately evaluate lightweight cement bonding. Oblique incidence is a new technology for evaluating cement quality with improved accuracy for lightweight cements. In this study, we simulated models of acoustic impedance of cement and cementing quality using ultrasonic oblique incidence, and we obtained the relation between cementing quality, acoustic impedance of cement, and the acoustic attenuation coeffi cient of the A0-mode and S0-mode Lamb waves. Then, we simulated models of different cement thickness and we obtained the relation between cement thickness and the time difference of the arrival between the A0 and A0′ modes.

Microstructural evolution of 2519-T87 aluminum alloy obliquely impacted by projectile with velocity of 816 m/s

Target made of 2519-T87 aluminum alloy was obliquely impacted by a projectile. Microstructural evolution around the crater was investigated by optical microscopy （OM）, transmission electron microscopy （TEM）, and electron backscattered diffraction （EBSD）. The micro-hardness distribution near the crater after impact was studied. The results indicate that at the entering stage, the amount of adiabatic shear band （ASB） is the most, and the precipitates are as fine as those of the target material; the micro-hardness is higher than that at the other stages. At the stable-running stage, the amount of ASB reduces as the micro-bands increase; the precipitates tend to coarsen, which leads to the decrease of the micro-hardness. At the leaving stage, there is a large amount of micro-bands; the precipitates are refined, and the micro-hardness is higher than that at the stable-running stage. The difference in the micro-hardness of the impact stages is due to work hardening and precipitate coarsening, which is caused by adiabatic temperature rise in the alloy.

基于Oblique显示技术的钝性外伤患者肋骨隐匿性骨折的影像诊断及其分型研究

目的:应用Oblique显示技术对肋骨隐匿性骨折进行诊断及分型。方法:选取2014年3月-2018年12月就诊于本院106例明确钝性外伤史疑似肋骨隐匿性骨折患者,所有患者经常规显示技术均未发现肋骨骨折。所有患者应用Oblique显示技术检查进行肋骨隐匿性骨折诊断,并根据骨折累及程度及表现形式进行肋骨隐匿性骨折分型。结果:106例患者共有189根肋骨存在隐匿性骨折,分为单皮质缘骨折、双皮质缘骨折及钝性骨挫伤。其中单皮质缘骨折105根,包括单纯外缘骨皮质褶皱成角64根,内缘骨皮质褶皱成角41根;内缘及外缘同时褶皱成角的双皮质缘骨折55根;骨皮质缘光滑无褶皱,仅表现为髓腔内骨髓水肿的钝性骨挫伤29根。结论:Oblique显示技术可以提高肋骨隐匿性骨折的诊断率,并能依据累及程度及表现形式进行合理分型。

The criterion of the existence or inexistence of transverse shock wave at wedge supported oblique detonation wave

A simplified theoretic method and numerical simulations were carried out to investigate the characterization of propagation of transverse shock wave at wedge supported oblique detonation wave.After solution validation,a criterion which is associated with the ratio Φ （u 2 /u CJ） of existence or inexistence of the transverse shock wave at the region of the primary triple was deduced systematically by 38 cases.It is observed that for abrupt oblique shock wave （OSW）/oblique detonation wave （ODW） transition,a transverse shock wave is generated at the region of the primary triple when Φ 〈 1,however,such a transverse shock wave does not take place for the smooth OSW/ODW transition when Φ 〉 1.The parameter Φ can be expressed as the Mach number behind the ODW front for stable CJ detonation.When 0.9 〈 Φ 〈 1.0,the reflected shock wave can pass across the contact discontinuity and interact with transverse waves which are originating from the ODW front.When 0.8 〈 Φ 〈 0.9,the reflected shock wave can not pass across the contact discontinuity and only reflects at the contact discontinuity.The condition （0.8 〈 Φ 〈 0.9） agrees well with the ratio （D ave /D CJ） in the critical detonation.

Reflection of Oblique Incident Waves by Breakwaters with Partially-Perforated Wall

The reflection of oblique incident waves from breakwaters with a partially-perforated front wall is investigated. The fluid domain is divided into two sub-domains and the eigenfunction expansion method is applied to expand velocity potentials in each domain. In the eigen-expansion of the velocity potential, evanescent waves are included. Numerical results of the present model are compared with experimental data. The effect of porosity, the relative chamber width, the relative water depth in the wave absorbing chamber and the water depth in front of the structure are discussed.

Periodic oscillation and fine structure of wedge-induced oblique detonation waves

An oblique detonation wave for a Mach 7 inlet flow over a long enough wedge of 30 turning angle is simulated numerically using Euler equation and one-step rection model.The fifth-order WENO scheme is adopted to capture the shock wave.The numerical results show that with the compression of the wedge wall the detonation wave front structure is divided into three sections：the ZND model-like strcuture,single-sided triple point structure and dual-headed triple point strucuture.The first structure is the smooth straight,and the second has the characteristic of the triple points propagating dowanstream only with the same velocity,while the dual-headed triple point structure is very complicated.The detonation waves facing upstream and downstream propagate with different velocities,in which the periodic collisions of the triple points cause the oscillation of the detonation wave front.This oscillation process has temporal and spatial periodicity.In addition,the triple point trace are recorded to obtain different cell structures in three sections.

Oblique perforation of thick metallic plates by rigid projectiles

Oblique perforation of thick metallic plates by rigid projectiles with various nose shapes is studied in this paper. Two perforation mechanisms, i.e., the hole enlargement for a sharp projectile nose and the plugging formation for a blunt projectile nose, are considered in the proposed analytical model. It is shown that the perforation of a thick plate is dominated by several non-dimensional numbers, i.e., the impact function, the geometry function of projectile, the non-dimensional thickness of target and the impact obliquity. Explicit formulae are obtained to predict the ballistic limit, residual velocity and directional change for the oblique perforation of thick metallic plates. The proposed model is able to predict the critical condition for the occurrence of ricochet. The proposed model is validated by comparing the predictions with other existing models and independent experimental data.

The force of oblique incident wave on the breakwater with a partially perforated wall

Wave forces induced by the interaction between the oblique incident wave and the breakwater with a partially perforated front wall is investigated. The fluid domain is divided into two sub-domains and the eigen-function expansion method is applied to expanding velocity potentials in each domain. In the eigen-expansion of the velocity potential, evanescent waves are included. Numerical results of the present model are compared with other theories and a good agreement can be found between them. Experimental data have been compared with the present theoretical results. The effect of the traverse wall on wave forces has been discussed in detail. On the basis of the linear wave theory, it is shown that in the range Of engineering practice, the incident angle of wave has small influence on wave forces on the unit length of perforated caisson.

Inferior oblique weakening surgery on ocular torsion in congenital superior oblique palsy

AIM: To investigate changes in fundus excyclotorsion after inferior oblique myectomy or myotomy. METHODS: The records of 21 patients undergoing strabismus surgery by a single surgeon between 2009 and 2012 were examined. Only patients who had undergone an inferior oblique myectomy or myotomy,with or without horizontal rectus muscle surgery, were evaluated. Digital fundus photographs were obtained,and the angle formed by a horizontal line passing through the optic disc center and a reference line connecting the foveola and optic disc center was measured. Associated clinical factors examined include age at the time of surgery, presence or absence of a head tilt, degree of preoperative vertical deviation,torsional angle, inferior oblique muscle overaction/superior oblique muscle underaction, and surgery laterality. Whether the procedure was performed alone or in combination with a horizontal rectus muscle surgery was also examined. RESULTS: Mean preoperative torsional angle was12. 0 ± 6. 4 °, which decreased to 6. 9 ± 5. 7 ° after surgery(P 【0.001, paired t-test). Torsional angle also decreased from 15. 1 ± 7. 0 ° to 6. 2 ± 4. 3 ° in the myectomy group(P 【0.001, paired t-test) but there were no significant changes in the myotomy group(P =0.093, Wilcoxon signed rank test). Multivariable linear regression analysis showed that preoperative torsional angle, degree ofinferior oblique overaction, and age at surgery independently and significantly affected postoperative torsional angle.CONCLUSION: Mean torsional angle decreased after inferior oblique myectomy. Degree of preoperative torsional angle, inferior oblique overaction, and age at surgery influence postoperative torsional angle.

Characteristics and mechanism investigation on drag reduction of oblique riblets

This work primarily focuses on the drag reduction characteristics and mechanism investigation of oblique riblets. First, a calculation model of the oblique riblets surface is established, and Reynolds stress model(RSM) turbulence model is used for numerical simulation of the oblique riblets flow field. Subsequently, the influence of inclination angle between flow direction and arrangement direction of riblets on friction resistance and drag reduction rate is further analyzed. Through the investigation of the distribution of shear stress, pressure stress and velocity in oblique riblets boundary layer, the oblique riblets drag reduction mechanism is finally revealed. Results show that, with increase of velocity and inclination angle, the pressure resistance increases obviously, along with the decreasing of the viscous resistance distinctly. The maximum drag reduction rate of the oblique riblets is 7.33%. Moreover, when the inclination angle increases, the wall shear stress reduces on oblique riblets surface; while differential pressure increases at both sides of oblique riblets tips. In addition, when inclination angle is small, the secondary vortex at oblique riblets tips will disappear soon. New vortices will be formed inside the oblique riblets and cause the decrease of viscosity resistance. Thus, oblique riblets show a better drag reduction effect and have an effective control on boundary layer.

Three - dimensional numerical simulation of oblique wave action on vertical walls

A three-dimensional numerical model based on the potential theory was developed to study the oblique wave action on vertical walls. A source term inside the domain was used to generate incident waves and outgoing waves were dissipated by sponge layers and transmitted by radiation boundaries. The finite difference method was used to solve the governing equations and boundary conditions in the regular transformed domain in σ-coordinate. Satisfactory agreements between the numerical predictions and experimental results of wave force were obtained. It is concluded that the maximum wave force acting on the vertical walls is induced by the obliquely incident waves rather than the normally incident waves.

Surgical outcomes for unilateral superior oblique palsy in Chinese population: a retrospective study

AIM: To evaluate the outcome after surgery for unilateral superior oblique(SO) palsy in Chinese.METHODS: The medical records of 39 patients that underwent surgery for unilateral SO palsy between January 2003 and December 2012 at Caritas Medical Centre, Hong Kong, were retrospectively reviewed. All surgeries were performed by a single surgeon. Pre-operative assessments for vertical deviation, cyclo-deviation, and Knapp’s classification were obtained to determine the nature and degree of surgical correction.Vertical deviation was measured at 1wk; 1, 6mo and on last follow-up day post-operatively. Cyclo-deviation was measured on last follow-up day post-operatively.RESULTS: During the 10 y period, 39 subjects were recruited. The most common etiology was congenital(94.9%). Knapp’s Type III(66.7%) and Type I(12.8%)classifications were the most common subtypes. To treat SO palsy, the most common surgical procedures were:isolated inferior oblique(IO) anteriorization(41.0%),isolated IO myectomy(10.3%), and isolated IO recession(10.3%). At 3.5 ±2.1y post-operatively, the vertical deviation was significantly reduced(15.1 ±6.2 PD versus0.5±1.4 PD, P 【0.0001) without significant improvement in cyclo-deviation(P =0.5). Initial vertical deviation was correlated with cyclo-torsion(r =0.4, P =0.007). Those with over-correction had greater initial vertical deviation(19.4±7.2 PD versus 13.2±4.3 PD, P =0.003). After a single operation, 84.6% of subjects achieved a vertical deviation within ±3 PD.· CONCLUSION: The majority of subjects achieved corrected vertical deviation after a single surgery although there was no improvement in cyclo-deviation.Those with over-correction of primary position deviation had greater preoperative vertical deviation and it may be related to simultaneous multiple muscle surgery.

Physical Modeling of Landslide Mechanism in Oblique Thick-Bedded Rock Slope: A Case Study

The Jiweishan landslide illustrates the failure pattern of an apparent dip slide of an oblique thick-bedded rockslide. Centrifugal modeling was performed using a model slope consisting of four sets of joints to investigate the landslide initiation mechanism. Crack strain gauges pasted between the slide blocks and the base failed in sequence from the rear to the front as the centrifugal acceleration increased. When the acceleration reached 16.3g, the instantaneous failure of the key block in the front triggered the apparent dip slide of all blocks. The physical modeling results and previous studies suggest that the strength reduction in the weak layer and the failure of the key block are the main reasons for the Jiweishan landslide. The centrifuge experiment validated the previously proposed driving-blocks-key-block model of apparent dip slide in oblique with inclined bedding rock slopes. In addition, the results from limit equilibrium method and centrifuge test suggest that even though the failure of the key block in the front is instantaneous, a progressive stable-unstable transition exists.

Propagation characteristics of oblique incidence terahertz wave through non-uniform plasma

The propagation characteristics of oblique incidence terahertz(THz) waves through non-uniform plasma are investigated by the shift-operator finite-difference time-domain(SO-FDTD) method combined with the phase matching condition.The electron density distribution of the non-uniform plasma is assumed to be in a Gaussian profile. Validation of the present method is performed by comparing the results with those obtained by an analytical method for a homogeneous plasma slab.Then the effects of parameters of THz wave and plasma layer on the propagation properties are analyzed. It is found that the transmission coefficients greatly depend on the incident angle as well as on the thickness of the plasma, while the polarization of the incident wave has little influence on the propagation process in the range of frequency considered in this paper. The results confirm that the THz wave can pass through the plasma sheath effectively under certain conditions,which makes it a potential candidate to overcome the ionization blackout problem.

Penetration of sandwich plates with hybrid-cores under oblique ballistic impact

The oblique penetration performance of lightweight hybrid-cored sand- wich plates are investigated numerically. To compose the hybrid-core, ceramic prisms are inserted into pyramidal metal lattice trusses and fixed using epoxy resin. Three-dimensional finite element simulations are carried out for the hybrid- cored sandwich impacted at 15°, 30°, 45°, and 60°obliquity by a hemispherical projectile. The ballistic limit, the energy absorbed by the constituting elements, and the critical oblique angle are quantified. The physical mechanisms underly- ing the failure and the influence of fundamental system parameters are explored. The angle of obliquity is found to have significant influence on the ballistic trajec- tory and erosion of the projectile, thus it is important for the impact response and penetration resistance of the sandwich. For oblique angles equal to or larger than 45°, the projectile moves mainly horizontally and can not effectively penetrate across the sandwich.

Seismic stability of jointed rock slopes under obliquely incident earthquake waves

Seismic stability of slopes has been traditionally analyzed with vertically propagated earthquake waves.However,for rock slopes,the earthquake waves might approach the outcrop still with a evidently oblique direction.To investigate the impact of obliquely incident earthquake excitations,the input method for SV and P waves with arbitrary incident angles is conducted,respectively,by adopting the equivalent nodal force method together with a viscous-spring boundary.Then,the input method is introduced within the framework of ABAQUS software and verified by a numerical example.Both SV and P waves input are considered herein for a 2 D jointed rock slope.For the jointed rock mass,the jointed material model in ABAQUS software is employed to simulate its behavior as a continuum.Results of the study show that the earthquake incident angles have significance on the seismic stability of jointed rock slopes.The larger the incident angle,the greater the risk of slope instability.Furthermore,the stability of the jointed rock slopes also is affected by wave types of earthquakes heavily.P waves induce weaker responses and SV waves are shown to be more critical.