Dome Surface Research Articles

3D DATA INTERPRETATION USING TREATISES GEOMETRIC RULES TO BUILT COFFERED DOMES

Abstract. The contribution is part of a research that aims to address the problems of knowledge, interpretation and documentation of coffered domes geometry. The main question is to define the relationships between the coffer shape, the layout used for coffers distribution on dome surface and different kind of surfaces. With regard to coffered domes we have analyzed the methods illustrated by Francesco Milizia, Giuseppe Vannini and some historical surveys. We have grouped coffered domes in relation to grid geometry and to coffer shape. We have defined three different ways to distribute the coffers in relation to different grid layout: grid composed by 2D lines (meridians and parallels), grid composed by 3D lines on surface (lattice of rhumb lines) or coffers distribution between ribs. We have analyzed each of them and we have defined algorithmic models in relation to spherical domes. The main goal of our research is to study what's different in not spherical domes, such as policentrical domes, ellipsoidal domes or ovoidal domes, generated using curves network. We have compared computational models based on treatises rules with particular case studies. This comparison allows us to do a critical analysis based on geometric rules. From a methodological point of view we have built a parametric model able to connect the different processes, using the same parameters. By comparing this model with point clouds, it is possible to evaluate analogies or identify new rules that will be used to develop a more complex parametric model based on surveys.

Development of a simplified, reproducible, parametric 3D model of the talus

Computational foot models have significant application in surgical decision making, injury and disease diagnosis and prevention, sports performance analysis and footwear engineering. However, due to the substantial time in model building and the heavy computational costs from the complexity of the models, daily clinical application of these foot models has yet to be achieved. Much of the previous research adopted a detailed-geometry approach in modeling bones that potentially contributed to the heavy computational costs. In this research, we developed a computational talus model based on CT section image data, image reconstruction and segmentation, contact surface identification, standard shape fitting, and finite element auto meshing algorithms. Modeling the bones as rigid is common, and modeling the contact surfaces only for the rigid body saves additional computational resources. Priority, therefore, in the shape fitting with optimization is given to the contact surfaces of the talus. Thirteen sets (9 males and 4 females) of CT section data were obtained. Image reconstruction, segmentation and bone labeling were conducted on each set of CT data to identify talus and its adjacent bones. Contact surfaces of the talus were then identified based on bone spatial relationships. Apart from the talar dome surface which was fitted by a 3rd-order polynomial, standard shapes such as ellipsoids and planes were used to fit the selected contact surfaces so that the geometrical parameters maintain physical significance. Based on these parameters, we automatically recreated and meshed the least-squares fitted shapes rapidly with limited elements. Last, mean major contact surfaces of the talus were obtained and fitted by standard shapes. Although the number of samples in this study was relatively small, our method provides sufficient and accurate geometric parameters of these contact surfaces to completely describe and reproduce the talus, on both a subject specific and average basis. The method for describing the talus here helps to parametrize computational models using planes and ellipsoids, improves surgical decision making and implants with a more precise and physically significant measures, and the description provides bone geometric parameters which can later be used to relate risk analysis for bone shape specific injury rates.

Slurry extrusion on Ceres from a convective mud-bearing mantle

Ceres is a 940-km-diameter dwarf planet that is predominantly composed of silicates and water ice. In Ceres’ partially differentiated interior, extrusive processes have led to the emplacement on its surface of domes with heights of kilometres. Here we report the analysis of a gravity anomaly detected by the Dawn spacecraft, which is associated with the geologically recent dome Ahuna Mons. By modelling the anomaly with a mass concentration method, we determine that the subsurface structure includes a regional mantle uplift, which we interpret as a plume. This structure is the probable source of fluids forming Ahuna Mons and, together with constraints from the dome’s morphology, indicates a rheological regime corresponding to a slurry of brine and solid particles. We propose that the properties of such a solid–liquid mixture can explain the viscous relaxation and the mineralogy of the dome. The presence of a plume and of slurry material indicate recent convection in a mud-bearing mantle. The inferred slurry extrusion on Ceres differs from the water-dominated cryovolcanism of icy satellites, and so reveals compositional and rheological diversity in extrusive phenomena on planetary surfaces. Ahuna Mons dome on Ceres formed by extrusion of a mixture of brine and solids sourced from a muddy mantle plume, according to numerical modelling of slurry rheology and a gravity anomaly found by the Dawn mission.

LAVA DOME CHANGES DETECTION AT AGUNG MOUNTAIN DURING HIGH LEVEL OF VOLCANIC ACTIVITY USING UAV PHOTOGRAMMETRY

Abstract. Lava dome changes detection during increasingly high volcanic activity are essential for hazard assessment purposes. However, it is challenging to conduct direct field measurement due to safety reason. Here, we investigate the lava dome changes of Mount Agung in Indonesia during the highest level of volcanic activity. On 22 September 2017, the rumbling and seismic activity in this volcano started increasing to the highest level for a period of time. We afterwards collected image data at lava dome area by using UAV over this time period. To accomplish the goal of change detection, we assembled and developed a fixed-wing UAV platform, i.e. Buffalo FX-79 to acquire images of Mount Agung whose elevation is roughly 3,142 m above sea level. We acquired the UAV images on two dates, i.e. Oct 19 and Oct 21 of 2017. Due to an exclusion zone surround the volcano, we could only operate the UAV at 20 km distance from the crater. With these data set, we produced three-dimensional point clouds, high-resolution Digital Elevation Model and orthophoto by using Structure from Motion (SfM) and Multi View Stereo (SfM-MVS) technique with Photoscan Pro software. From orthophoto data, we found two fluid areas at the crater's surface in NE direction (4,375.9 sq-m) and SE direction (3,749.8 sq-m). We also detected a fumarole which emitted steam and gases in the eastern part that continued for several days. In order to reveal the changes in lava dome surface, we used DEM to create cross-section profile. After that, we applied cloud to cloud comparison (C2C) algorithm to calculate the difference of lava dome based on two data set of point clouds and compared it with interferometric result from Sentinel-1A data. The data from the Sentinel-1A satellite (15 Oct – 27 Oct 2017) were processed to obtain the interferogram image of Mount Agung. This research therefore demonstrates a potential method to detect lava dome changes during high level of volcanic activity with photogrammetric methods by using UAV images. Within only two days the data were successfully acquired. From the DEM data and cross-section profile between two data set, we noticed that no significant surface change was found around the lava dome surface. Moreover, we also found that there was no significant lava dome changes and vertical displacement during these two time periods as the point cloud comparison and distance result. The average of difference distance is 2.27 cm with a maximal and minimal displacement of 255 cm and 0.37 cm respectively. This result was then validated by using InSAR Sentinel that showed small displacement, i.e 6.88 cm. It indicated that UAV photogrammetry showed a good performance to detect surface changes in centimeter fraction.

Dynamic structural responses of long-span dome structures induced by tornadoes

Long-span dome structures are widely used for public assembly venues because of their large column-free space and efficient use of materials. When occupied by hundreds or even thousands of people, it would be devastating if they fail or collapse, which unfortunately happen frequently during extreme events, especially under tornadic winds. Although static effects of tornadoes on civil structures have been extensively studied, their dynamic impact has not been sufficiently investigated. In this study, non-stationary characteristics of tornadoes and their dynamic impact on a long-span dome structure are systematically investigated. In particular, the time-variant wind pressure on the dome surface induced by translating tornadoes with different intensities is characterized through Computational Fluid Dynamics simulations. The obtained wind pressure is then mapped onto the finite element model of the dome structure, and transient time-history analyses are conducted to characterize the tornado-induced dynamic responses. It is observed that non-stationary wind pressure and the induced dynamic structural responses are significant, when core radius of the tornado approaches the dome. Wind flow of EF4 and EF5 tornadoes is found to be more turbulent than EF2 and EF3 tornadoes, and hence larger and more rapid fluctuations of dynamic responses.

Advanced Applications of Synthetic Aperture Radar (SAR) Remote Sensing for Detecting Pre- and Syn-eruption Signatures at Mount Sinabung, North Sumatra, Indonesia

DOI:10.17014/ijog.6.2.123-140Mount Sinabung was re-activated at August 28th, 2010 after a long repose interval. The early stage of a phreatic eruption was then followed by magmatic eruptions at September 15th, 2013 for years until now. To understand the ground surface changes accompanying the eruption periods, comprehensive analyses of surface and subsurface data are necessary, especially the condition in pre- and syn-eruption periods. This study is raised to identify ground surface and topographical changes before, intra, and after the eruption periods by analyzing the temporal signature of surface roughness, moisture, and deformation derived from Synthetic Aperture Radar (SAR) data. The time series of SAR backscattering intensity were analyzed prior to and after the early eruption periods to know the lateral ground surface changes including estimated lava dome roughness and surface moisture. Meanwhile, the atmospherically corrected Differential Interferometric SAR (D-InSAR) method was also applied to know the vertical topographical changes prior to the eruptions. The atmospheric correction based on modified Referenced Linear Correlation (mRLC) was applied to each D-InSAR pair to exclude the atmospheric phase delay from the deformation signal. The changes of surface moistures on syn-eruptions were estimated by calculating dielectric constant from SAR polarimetric mode following Dubois model. Twenty-one Phased Array type L-band SAR (PALSAR) data on board Advanced Land Observing Satellite (ALOS) and nine Sentinel-1A SAR data were used in this study with the acquisition date between February 2006 and February 2017. For D-InSAR purposes, the ALOS PALSAR data were paired to generate twenty interferograms. Based on the D-InSAR deformation, three times inflation-deflation periods were observed prior to the early eruption at August 28th 2010. The first and second inflation-deflation periods at the end of 2008 and middle 2009 presented migration of magma batches and dike generations in the deep reservoir. The third inflation-deflation periods in the middle of 2010 served as a precursor signal presenting magma feeding to the shallow reservoir. The summit was inflated about 1.4 cm and followed by the eruptions. The deflation of about 2.3 cm indicated the release pressure and temperature in the shallow reservoir after the early eruption at August 28th, 2010. The last inflation-deflation period was also confirmed by the increase of the lava dome roughness size from 5,121 m2 on July to 6,584 m2 on August. The summit then inflated again about 1.1 cm after the first eruption and followed by unrest periods presented by lava dome growth and destruction at September 15th, 2013. The volcanic products including lava and pyroclastics strongly affected the moisture of surface layer. The volcanic products were observed to reduce the surface moisture within syn-eruption periods. The hot materials are presumed responsible for the evaporation of the surface moisture as well.

Effect of Increased Density of Nodes in Geodesic Dome on its Critical Load Capacity

The paper reports an attempt at assessing the effect of geodesic dome mesh refinement on the structure critical load capacity. The initial surface of geodesic domes is the sphere divided into spherical triangles. Consecutive divisions of the spherical triangles decide the mesh refinement of the geodesic domes. Two computational models (3V and 4V) were examined. For 4V dome, two types of structure, namely truss and frame ones were considered. For 4V frame system, the values of the critical load capacity were determined for three buckling lengths of the bars μ: 0.5, 0.7 and 1.0.

The gastric sieve of penaeid shrimp species is a sub-micrometer nutrient filter.

Unlike that of vertebrates, the penaeid shrimp stomach is of ectodermic origin and is thus covered by a cuticle that is sloughed upon molting. It is composed of two chambers, here called the anterior and posterior stomach chambers, ASC and PSC, respectively. The PSC contains a filtration structure variously called a pyloric filter, filter press, gastric filter or gastric sieve (GS), and the last of these will be used here. The GS resembles an elongated, inverted-V, dome-like, chitinous structure with a midline ridge that is integral to the ventral base of the PSC. The dome surface is covered with a carpet-like layer of minute, comb-like setae bearing laterally branching setulae. This carpet serves as a selective filter that excludes large partially digested food particles but allows smaller particles and soluble materials to enter hepatopancreatic ducts that conduct them into the shrimp hepatopancreas (HP), where further digestion and absorption of nutrients takes place. Although the GS function is well known, its exclusion limit for particulate material has not been clearly defined. Using histological and ultra-structure analysis, we show that the GS sieve pore diameter is approximately 0.2-0.7 µm in size, indicating a size exclusion limit of substantially less than 1 µm. Using fluorescent microbeads, we show that particles of 1 µm diameter could not pass through the GS but that particles of 0.1 µm diameter did pass through to accumulate in longitudinal grooves and move on to the HP, where some were internalized by tubule epithelial cells. We found no significant difference in these sizes between the species Penaeus monodon and Penaeus vannamei or between juveniles and adults in P. vannamei This information will be of value for the design of particulate feed ingredients such as nutrients, therapeutic drugs and toxin-absorbing materials that may selectively target the stomach, intestine or HP of cultivated shrimp.

Process Planning of Creating a Surface Dome with Bead Deposition Additive Manufacturing

Abstract Bead deposition additive manufacturing processes deposit material from a machine head onto the substrate to make the product. This can encompass plastic materials or metal powder via a direct metal deposition process. In order to minimize or even eliminate the need for support structures in making complex parts, a 5 axis motion between the machine head and substrate is needed for components with overhanging geometry. Providing 5 axis movement increases the flexibility of the machine in such a way that the nozzle axis and the substrate normal do not exceed the maximum allowed overhang angle. This eliminates or reduces the need for support structure for making complex parts. However, 5 axis machines increase the complexity of the process and the possibility of a collision between the machine head, the substrate, or previously deposited layers. This paper focuses on process planning of complex parts in order to eliminate a collision condition. As a case study the methodology is applied to build a surface dome by a 5 axis bead deposition based additive manufacturing. Partitioning strategies are applied to eliminate the collision possibility while addressing the construction of overhanging geometry.

Astroclimate Studies in the Special Astrophysical Observatory of the Russian Academy of Sciences

The results of measurements of astroclimate characteristics in the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO, North Caucasus) in 2012 and 2016 are presented. The experimental results are obtained from long-term observation series of the day and night astroclimate in the SAO. The presence of non-Kolmogorov coherent turbulence was detected over the SAO site, in which the quality of telescope images improved. The effect of the underlying surface type and wind direction on the conditions for coherent turbulence origination is explained by the mountainous terrain and nonuniform heating of the underlying surface. The airflow velocity distribution inside the dome room of the Big Telescope Alt-azimuth (BTA) was experimentally studied. The air-mass trajectories inside the BTA dome room were numerically simulated to analyze the effect of the temperature regime and construction geometry. The solutions of the boundary problem confirm the existence of an experimentally detected vortex structure with a vertical rotation axis. The causes for its generation are the temperature gradients of the dome surfaces.

Numerical analysis of thermal radiation noise of shock layer over an infrared optical dome at near-ground altitudes

To examine the effect of atmospheric trace species on the infrared thermal radiation of a supersonic dome, a series of radiation characteristics with different geometry sizes at near-ground altitudes were investigated numerically. The conjugate heat transfer method was applied to build the heat transfer model of the optical dome. Three major radiating species of H2O, CO2, and CO were taken into account in the shock layer. A line-by-line (LBL) method was used for evaluating the radiative properties of species. A line-of-sight (LOS) approach was applied to solve the radiative transfer equation (RTE). The simulated and measured results of the dome were also proposed to validate the numerical method. The effects of the dome geometry size, the dome material and the time-varying altitude on the infrared radiation noise were studied in detail. The results show that the altitude-varying radiation intensity along the LOS is related to the ambient density and velocity. The variation of the dome radius is proportional to the total radiation received on the dome surface. It is observed that the maximum radiation intensity along the LOS does not occur in the normal direction of the receiving point, but it is determined by both the flow field parameters and the path length. Also, the radiation increment corresponding to different dome sizes approximately obeys a Gaussian distribution related to the product of density and velocity.

Time Dependence of Passive Degassing at Volcán Popocatépetl, Mexico, From Infrared Measurements: Implications for Gas Pressure Distribution and Lava Dome Stability

AbstractThe transport and storage of gas within lava domes is critical to their stability or explosivity. To analyze gas flow through these systems, degassing from Volcán Popocatépetl, Mexico, is studied here. Short‐duration (hours) passive degassing at Popocatépetl is dominated by oscillating components with periods between 100 and 1,000 s in agreement with similar measurements across a range of other volcanic systems. Over these timescales, porous gas flow through an idealized dome obeys a nonlinear diffusion equation. Approximate solutions contain series of diffusive pressure waves which decay to a steep boundary layer near the dome surface. Wave behavior is governed by the oscillation period and dome rock permeability, acting as a low‐pass filter on flux oscillations. This may explain the weakness of higher‐frequency (>0.01 Hz) oscillations in the Popocatépetl degassing data. These waves are shown to significantly modify the dome effective strength. For ∼100‐m‐radius domes, the pore pressure is comparable to the overburden, and the total strength of the dome is dominated by tensile strength. The pressure in smaller domes (≪100 m) dominates and may induce failure. This may explain observations of extrusion and destruction cycling during dome‐producing eruptions. The difference between pore pressure and overburden exhibits a shallow (outermost 5–25%), high‐pressure layer which changes in size, shape, and overpressure magnitude throughout oscillations. Linear governing equations assumed by previous studies underestimate the pore pressure distribution and do not capture this shallow layer. Recognition of this layer allows for better understanding of the destabilization or explosion of pressurized lava domes.

Resorption behaviour of the articular surface dome and functional outcome after open reduction and internal fixation of mandibular condylar head fractures using small-fragment positional screws

PurposeThe aim of the study was to evaluate the resorption of the mandibular condylar head after open reduction and internal fixation of fractures with small-fragment screws and to evaluate the functional outcome. Patients and methodForty-eight patients (55 condylar head fractures) underwent surgical treatment. All kinds of complications were recorded. In a subgroup of 20 patients, the average loss of bone height of the condylar head joint surface was gauged by measuring the vertical distances from 3 selected reference points of the fixation hardware to the vertex of the condyle in views of multiplanar radiographs after 6 months. Functional outcome was analysed by Helkimo index score. ResultsComplication rates were low. Osteosynthesis loosening occurred in 4 cases. The mean bone resorption along the condylar head joint surface in the subgroup of 20 patients (with 23 joints) was 0.7 mm. Functional outcome was rated as follows: 8 patients - good, 11 patients – slightly impaired, 1 patient - moderately impaired. ConclusionOpen reduction and internal fixation of condylar head fractures with small-fragment screws leads to reliable results in terms of joint surfaces relatively resistant to resorption and function. Low bone resorption on the joint surface of the condylar head can be expected.

The central pit and dome at Cerealia Facula bright deposit and floor deposits in Occator crater, Ceres: Morphology, comparisons and formation

The prominent bright deposit Cerealia Facula, Ceres, coincides with the central depression (or central pit) of the recently formed 92 km-wide complex crater Occator. The central pit is 9–10 km wide and up to 1 km deep and is partially filled with a 700 m-high 2 km-wide dome. The upper surface of the central dome is densely fractured but the flanks are not, indicating that uplift of the dome surface occurred after the bright deposit was emplaced, and primarily through uplift of the surface from below by laccolithic intrusion or volume expansion. The pit is rimless except for two prominent massifs that flank it to the east and west. This pit-dome morphology bears a strong resemblance in morphology, topography, and dimensions to central pit craters observed on Ganymede and Callisto, but is essentially absent on the similar sized ice-rich moons of Uranus, Saturn, and Pluto. The lack of pit craters on midsize icy moons and the possible lack of central pit craters at the cold poles of Ceres suggest that temperature is a significant controlling factor in central pit formation, beyond the canonical inverse-gravity scaling of complex crater transitions. While renewed modeling will benefit from these new constraints, the mapping of central pits on Ceres, including Occator, suggests that either the rheologically layered target model or more likely the melted central uplift model may be the most probable explanation for central pit formation on Ceres (lack of similar high-resolution imaging on the Galilean icy satellites precludes definitive evaluation of models there). Large volumes of lobate floor-fill material at least 600 m thick in some places cover large areas of the southern and eastern floor of Occator, and small outcrops of this unit are found perched high on closed topographic depressions on the Occator terrace zone and other higher areas of the crater floor. The swirling and knobby surface textures of these lobate deposits are essentially indistinguishable from those on impact melt sheets on large lunar craters such as Tycho. These observations indicate that this unit is most likely an impact melt sheet formed from melted water ice admixed with unmelted particulate or dissolved phyllosilicates, salts and/or carbonates, and large quantities of fragmented debris. Melt of ice phases within Ceres crust is also supported by independent numerical models of impact at Occator and would provide a ready source of fluids to promote hydrothermal deposition of the observed bright Na-carbonates on the surface of the central pit at Occator, if the deposit formed within a million years or so of impact. The central dome finds analogs in salt domes on Earth and pingos (frost-mounds) on Earth and Mars, which form by water and solute migration and freeze expansion. Later freezing of a central reservoir of volatiles beneath the central pit at Occator or mobilization of ice or other phases during the cooling and refreezing process could explain the uplift of the central dome. Finally, no changes were detected in the Cerealia and Vinalia Facula bright deposits during the course of the prime Dawn mapping mission, placing additional constraints on their formation time and limits on ongoing activity.

Access to the talar dome surface with different surgical approaches

BackgroundAccess to the talar dome for the treatment of osteochondral lesions (OCLs) can be achieved via several different approaches to the ankle joint. The recent description of an anatomical nine-grid scheme of the talus has proven useful to localise OCLs but no studies have demonstrated which approaches are indicated to access each of these zones. The aim of this study is to demonstrate the access afforded to each zone by each approach. MethodsFour standard soft tissue ankle approaches were performed simultaneously in ten fresh-frozen cadavers (anterolateral — AL, anteromedial — AM, posterolateral — PL, posteromedial — PM). The area of the talus, which was accessible with an instrument perpendicular to the surface was documented for each of the approaches. Using ImageJ software the surface area exposed with each approach was calculated. The talar dome was then divided using a nine-grid scheme and exposure to each zone was documented. ResultsThe AL, AM, PL and PM approaches allow for exposure of 24%, 25%, 5%, 7% of the talar dome respectively. The AL gives access to zones 3 (completely) and 2, 5, 6 (partially); the AM to zones 1 (completely) and 2, 4, 5 (partially); the PL to zones 9 and 8 (partially); and the PM to zones 7 and 8 (partially). ConclusionsA large area of the talar dome cannot be easily accessed with the use of standard soft tissue approaches (39%). Minimal or no access is achieved for grid zones 4–6 and 8. In those instances careful preoperative planning is necessary and extended exposure can be achieved with the use of osteotomies, section of the ATFL or through modified approaches.

Gender Variation in the Shape of Superior Talar Dome: A Cadaver Measurement Based on Chinese Population.

Understanding the shape of superior talar dome is essential for a better size compatibility between talar component of ankle implant and bone. The purpose of this study was to determine whether there were gender variations in (1) width (TW) and length (TL) of talus, as well as anterior width (DAW), middle width (DMW), posterior width (DPW), and length (DL) of superior talar dome; (2) differences between the DAW, DMW, and DPW; (3) the ratios between these parameters. Fifty-one cadaveric ankle specimens were included. Two observers measured all the specimens using vernier caliper. Intraclass correlation coefficients (ICCs) were used for intraobserver and interobserver reliability analysis and the reliability was thought to be good if the ICC>0.75. A two-tailed unpaired t-test or the rank-sum test was used to investigate gender variations. A single-factor ANOVA was utilized to identify the differences between the width of the superior talar dome surface and p value of <0.05 was considered significant. Intraobserver and interobserver reliability were good. Significant gender variations were found, in which TW, TL, DAW, DMW, DPW, and DL of female specimens were much smaller than those of male. The width of talar dome linearly decreased from DAW to DPW; however, the linearly decreased rate from anterior to posterior width was bigger in female. Moreover, significant differences were found in DAW/DPW, DMW/DPW, DL/DAW, DL/DMW, and DL/DPW between male and female. Based on our result, there was no difference in the 2D shape of the whole talus instead gender variation existed in the 2D shape of superior talar dome between male and female. The current 2D data could contribute to figure out more suitable size of talar component for Chinese population and might indicate a gender-specific shape of bone-implant interface, which could reduce the potential bone-component incompatibility when performing ankle replacement using standard component.

Doing the Jitterbug with Islamic geometric patterns

ABSTRACTVertex-to-vertex polyhedral jitterbug transformations provide for the creation of polyhedra with specific angular conditions at the vertices that facilitate regions of local symmetry that are atypical of the spherical geometry associated with the Platonic and Archimedean polyhedra. This allows for the introduction of unexpected Islamic geometric designs comprised of primary stars with n-fold rotational symmetry that would not otherwise conveniently cover the surface of the sphere; for example, the regular distribution of twelve 7-pointed stars. These three-dimensional jitterbug transformations have two-dimensional corollaries that are instructive in understanding this design process. This expands upon the historical use among some Muslim cultures of polyhedral geometry as an organizing principle for placing geometric patterns onto the surfaces of domes and domical niches, and provides contemporary artists with a new approach to applying geometric design onto spherical surfaces.

DRAINABILITY OF PEAT DOME AREAS

Most of the large peat areas in Indonesia and Malaysia have a dome-shaped surface with an inverted saucer-shaped interface between the underlying peat/mineral contact. This results in the peat dome having a lens-shaped cross-section. The concept of drainability is determined by referring the elevation of the peat dome surface in relation to the mean height of the river level to which the peat dome is being drained to. Where this dome surface is lower than the mean elevation of the water in the river, backflow into the peat area can take place. With global warming and climate change being experienced these days, the development of peat swamps for agricultural activities may result in such a backflow. This is attributed to subsidence, decomposition and compaction of the peat after a period of agricultural development/activity having taken place. In the case of oil palm cultivation, the Roundtable on Sustainable Palm Oil (RSPO), or the Malaysian/Indonesian Sustainable Palm Oil (MSPO/ISPO) Certification Scheme and the Greenpeace initiative requires existing oil palm estates to conduct a drainability study to determine if the estate may in the future have backflow from the river into the estate. This determines the length of time the estate can use natural drainage and not resort to expensive pumping. This paper reviews the concept of drainability and the problems associated in determining the drainability of peat domes. The usage of instruments such as altimeter and global positioning system (GPS) are also discussed. With the advent of technology, the determination of drainability on peat dome is made easier but remain challenging e.g. hindering the drainability team to survey along the banks of the river by native peoples. A few examples from Malaysia also are presented in this paper. Keywords: Drainability, peat dome, oil palm, climate change, RSPO.

Simulation of ankle joint kinematics in sagittal plane using passive imaging data – a pilot study

Purpose: The purpose of this pilot study was to determine the radius of curvature of the tibia and talus, and to deduce ankle joint kinematics in the sagittal plane using passive imaging data. Methods: Imaging data of four subjects under passive conditions was used. Ligament positions were marked using MRI data to subscribe the four-bar linkage (FBL) mechanism at the ankle joint. Flexion motion of the assembly construct was simulated in the sagittal plane to determine the contact points on the tibial and talar dome surfaces. The radius of curvature was determined by fitting the contact points with a circle fit. Results: In addition to articular surfaces, calcaneofibular and tibiocalcaneal ligaments in the FBL play an important role in affecting the path of ankle joint motion. Two different linkage arrangements between the ligaments were observed in this study. The double-crank type arrangement by these ligaments generated the same contact path on the articular surface during dorsi- and plantarflexion, whereas the triple-rocker arrangement resulted in different paths. Conclusion: A higher order compliant mechanism, which includes additional ankle ligaments, needs to be developed and studied under load bearing conditions to achieve more accurate results.

Thermal influences on spontaneous rock dome exfoliation

Rock domes, with their onion-skin layers of exfoliation sheets, are among the most captivating landforms on Earth. Long recognized as integral in shaping domes, the exact mechanism(s) by which exfoliation occurs remains enigmatic, mainly due to the lack of direct observations of natural events. In August 2014, during the hottest days of summer, a granitic dome in California, USA, spontaneously exfoliated; witnesses observed extensive cracking, including a ~8000 kg sheet popping into the air. Subsequent exfoliation episodes during the following two summers were recorded by instrumentation that captured—for the first time—exfoliation deformation and stress conditions. Here we show that thermal cycling and cumulative dome surface heating can induce subcritical cracking that culminates in seemingly spontaneous exfoliation. Our results indicate that thermal stresses—largely discounted in dome formation literature—can play a key role in triggering exfoliation and therefore may be an important control for shaping domes worldwide.