Significant Discontinuities Research Articles

Numerical Predictions of Heat Transfer and Flow Structure in a Square Cross-Section Channel with Various Non-Spherical Indentation Dimples

The present study employs arrays of different shapes of surface dimples to determine the most optimal configurations for augmenting surface heat transfer rates, as pressure drop penalties are minimized. Six different dimple shapes are investigated (spherical indentation (case A), super-ellipse (case D), two ellipse-spherical arrangements with the long axis oriented both parallel and normal to the bulk flow direction (cases B1 and B2, respectively), and two egg-spherical arrangements with the half ellipse with longer axis pointed both away and towards the bulk flow direction (cases C1 and C2, respectively). The dimples in these arrays are aligned with each other, as they are located on one surface of a square cross-section channel in six different streamwise rows. All turbulent fluid flow and surface heat transfer results are obtained using computation fluid dynamics with a k−ϵ RNG turbulence model, and constant heat flux thermal boundary conditions applied to all channel surfaces. Flow development is provided, both before and after the middle channel section, which contains each dimple array. Numerically predicted results are qualified using grid-independent predictions of experimental data for one baseline dimple array arrangement. The channel inlet Reynolds number ranges from 8,000 to 24,000. The dimple shapes with the best overall performance (depending upon the Reynolds number and performance criteria considered) are the spherical indentation arrangement (case A), and the ellipse-spherical arrangement with the long axis oriented normal to the bulk flow direction (case B2). Overall, the most optimal heat transfer augmentations seem to occur when the largest indented cross-section area is oriented perpendicular to the streamwise direction, since larger areas are then available for shear layer re-attachment over downstream portions of the associated dimples. Also important for such augmentations are dimple surface geometry transitions and surface curvature diameters, as illustrated by thermal performance which decreases as surface shapes have more numerous or more significant discontinuities, or when local surface curvature diameters are too small. Overall, the present results also show that such configuration sensitivities appear to increase with Reynolds number.

Late Paleozoic to Jurassic chronostratigraphy of coastal southern Peru: Temporal evolution of sedimentation along an active margin

We present an integrated geochronological and sedimentological study that significantly revises the basin and magmatic history associated with lithospheric thinning in southern coastal Peru (15–18°S) since the onset of subduction at ∼530 Ma. Until now, estimating the age of the sedimentary and volcanic rocks has heavily relied on paleontologic determinations. Our new geochronological data, combined with numerous field observations, provide the first robust constraints on their chronostratigraphy, which is discussed in the light of biostratigraphical attributions. A detailed review of the existing local units simplifies the current stratigraphic nomenclature and clarifies its absolute chronology using zircon U–Pb ages. We observe that the Late Paleozoic to Jurassic stratigraphy of coastal southern Peru consists of two first-order units, namely (1) the Yamayo Group, a sedimentary succession of variable (0–2 km) thickness, with apparently no nearby volcanic lateral equivalent, and (2) the overlying Yura Group, consisting of a lower, 1–6 km-thick volcanic and volcaniclastic unit, the Chocolate Formation, and an upper, 1–2 km-thick sedimentary succession that are in markedly diachronous contact across the coeval arc and back-arc. We date the local base of the Chocolate Formation, and thus of the Yura Group, to 216 Ma, and show that the underlying Yamayo Group spans a >110 Myr-long time interval, from at least the Late Visean to the Late Triassic, and is apparently devoid of significant internal discontinuities. The age of the top of the Chocolate Formation, i.e. of the volcanic arc pile, varies from ∼194 Ma to less than ∼135 Ma across the study area. We suggest that this simplified and updated stratigraphic framework can be reliably used as a reference for future studies.

Cenozoic sedimentary evolution of deepwater sags in the Pearl River Mouth Basin, northern South China Sea

Recent exploration revealed the high potential for hydrocarbon in the deepwater sags, Pearl River Mouth Basin, northern South China Sea. This paper reports its Cenozoic sedimentary evolution through backstripping of high precision depth data of interpreted sequence boundaries. Local backstripping parameters were mapped based on well and geophysical data. Sensitivity analysis indicates that the reliability of decompaction results were largely improved by using the local porosity parameters and the lithological parameters that vary with grid nodes. Maps of sedimentation rates of 17 sequences from 65 Ma to the present were constructed, showing the spatial–temporal variation of the sedimentation rate. Three rapid depositional stages, 65–32, 29–23.3, 18.5–10.5 Ma, and three slow depositional stages, 32–29, 23.3–18.5, 10.5–0 Ma, were identified with abrupt changes of sedimentary patterns. The three rapid depositional stages were in accord with syn-rifting stage, the first post-rifting depositional stage, and the second post-rifting depositional stage, respectively. And the three slow depositional stages were in keeping with three tectonic events respectively. Several significant sedimentary discontinuities at 32, 23.3 and 10.5 Ma were observed and discussed. The comparison between the study area and the ODP Site 1148 at 32–23.3 Ma indicates that before ~29 Ma the ODP Site 1148 was at similar sedimentation regime as that in the Baiyun and Liwan sags, but significant diversity appeared after ~29 Ma, when a large quantity of terrigenous sediments was trapped by strong post-rifting subsidence in the Baiyun and Liwan sags and could not reach the lower slope areas. Study revealed that the most rapid accumulation from 18.5 to 17.5 Ma might be mainly owing to the large sediment supply during this strong monsoon period.

Bayesian image denoising using two complementary discontinuity measures

This study introduces a novel Bayesian image denoising method using two complementary discontinuity measures. The first discontinuity measure is the spatial-gradient, which has been widely used as a discontinuity measure. Although the spatial-gradient measure effectively preserves edge components in images, it is inadequate to detect significant discontinuities from noisy images because of its over-locality. Thus, the other discontinuity measure to detect contextual discontinuities for feature preservation is additionally required. The local-inhomogeneity measure provides the degree of uniformity in small regions, and is able to detect locations of the significant discontinuities effectively. Therefore the authors propose a Bayesian denoising framework using the two complementary discontinuity measures. The two complementary discontinuity measures are elaborately combined to be employed for creating prior probabilities of the Bayesian denoising framework. The experimental results show that the proposed method not only achieves a high peak signal to noise ratio (PSNR) gain from noisy images but also reduces noise effectively while preserving edge components.

Predicting blasting propagation velocity and vibration frequency using artificial neural networks

We describe artificial neural networks used to predict the velocity and frequency of ground vibrations caused by blasting in an open-pit mine. The aim was to predict peak particle velocity and frequency of ground vibrations from information on the physical and mechanical properties of the rock mass, the characteristics of the explosive and blasting design. Some the parameters that could possibly have a bearing on the prediction were considered. A distinction was drawn between two kinds of parameters: those defining the surroundings in which the wave is propagated (rock type, rock mass, distance to be covered by the wave and significant subsoil discontinuities) and those defining the energy of the wave (the kind of explosive, explosive charge and blasting geometry and sequence).Vibrations were monitored using seismographs capable of capturing vibration data and transforming them into acceleration and frequency terms. To validate this methodology, the predictions obtained were compared with those obtained using conventional statistical methods. The correlation coefficients obtained for our methodology was 0.98 for peak particle velocity and 0.95 for frequency, compared to 0.50 and 0.15, respectively, for Multiple Linear Regression.

Performance of pillar design in underground stone mines that include discontinuities

This paper describes a pillar design methodology that was developed from a study of pillar performance in operating stone mines. A number of methodologies have been developed to calculate full-scale mine pillar strengths based on laboratory scale strength obtained from specimens. Data were collected on rock mass quality, pillar conditions, mining dimensions and intact rock strength. Results showed that current mining practices have resulted in generally stable pillar layouts, without recent cases of extensive pillar collapses; however, failure of the pillars was found to be related to spalling of hard brittle rock, shearing along pre-existing angular discontinuities or progressive extrusion of soft infill material on bedding planes. A numerical model (FLAC3D) for the entire rock mass has been developed in order to analyze the stability of the entire underground opening. A preliminary monitoring phase has been realized, aimed at controlling abandoned rock structure movement at the most significant discontinuities. Some measurements of the vertical stress in the pillars and in the walls have also been performed and were used for model calibration. Once the model has been calibrated, analysis of the actual stress and deformation conditions can then be evaluated, the stability condition of the entire structure can be computed and a forecast analysis of what intervention could be realized to guarantee underground public access can be performed. The developed strength equation can be used to design stable pillar layouts, keeping in mind that the safety factor is greater than 1.5 and the width:height ratio of the pillars is between 0.6 and 0.8. It is concluded that, by applying the developed equation and selecting appropriate input parameters, it should then be possible to calculate the factor of safety.

SU-E-T-518: Dose Perturbation at Air-Tissue Interface in Proton Beam Therapy.

The loss of transverse equilibrium along the central axis of the proton beam in the presence of the air/tissue interface creates dose perturbation that has not been fully quantified. This gets magnified in small fields that are used for lung and patch up fields. Air-tissue dose perturbation is studied in a phantom and verified with Monte Carlo simulation. Air channel of variable thickness that could be found in trachea, larynx and small lesions in lung were studied. To mimic air/tissue interface a simple phantom geometry was used with EBT films. The results confirmed the presence of dose perturbations which were investigating using water phantom in reference condition (10×10 cm2 field, 16 cm range and 10 cm SOBP). A variable air column was created in the front of the phantom. A small volume ion chamber was used to collect high resolution profile data in water. The simulation was performed with 3×10̂7 particles with the Monte Carlo particle transport code FLUKA version 2011.2.10 with cut off energy of 100keV. The dose perturbations were visible on film and quantified by ion chamber measurements in water. Dose perturbations at air-tissue interfaces are shown to be significant (-20 to +30%). The measured profiles show significant discontinuities in dose up to +30% in low density medium. The magnitude is dependence on the location and width of the air gap. Under and over dose perturbation pattern is not predicted by treatment planning system (TPS) due to proton transport algorithm and calculation bin. The Monte Carlo simulation confirmed our measured data. Significant dose perturbation exists with high-dose region in low density medium that is not predicated by TPS. The magnitude and shape is position and gap size dependent. This study provides the presence of dosimetric discontinuities that should be evaluated clinically at interfaces.

The role of institutional, family and peer-based discourses and practices in the construction of students' socio-academic trajectories

In this article, we discuss findings from multi-level ethnography conducted in a secondary school located in Madrid (Spain). The study focuses on the variety of institutional, family and peer-based factors that contribute to the construction of students' socio-academic trajectories. In particular, we attempt to understand the role these social fields play in the construction of educational careers that are comparatively less successful in the case of immigrant students. Our findings suggest that these ‘objective outcomes’ are immersed in a web of discourses, practices and representations held by educators, parents and students about the future, the role of schooling in adolescents socio-educational paths and the interconnections between each social field (school, parents and peers) that show significant contradictions and discontinuities. In our analysis, we uncover some of these tensions and examine the role they play in the configuration of adolescent's educational subjectivities.

Influence of changes in the station location and measurement routine on the homogeneity of the temperature, wind speed and precipitation time series

Received 31 May 2012, in revised form 28 August 2012 Abstract. Changes in the location, instrumentation and measurement times are documented for three Estonian meteorological stations during the last century. These metadata were used to check if such changes have introduced significant discontinuities into the time series of daily and monthly mean temperature, average wind speed and daily and monthly precipitation sums. For this purpose, time periods of the length of at least ten years were separated before and after each change and average values of meteorological elements during these periods were compared by means of the t- test at the significance level of 0.05. On the daily basis, such changes introduced an increase in all parameters under consideration. On the monthly basis, only wind speed and precipitation sums were affected in some cases. Earlier climatological analyses have shown that in Estonia the tem- perature has risen and the precipitation sums have increased. Therefore, it is very difficult to separate natural trends from the artificial changes.

Reappraisal of the Somatosensory Homunculus and Its Discontinuities

Neuroscience folklore has it that somatotopy in human primary somatosensory cortex (SI) has two significant discontinuities: the hands and face map onto adjacent regions in SI, as do the feet and genitalia. It has been proposed that these conjunctions in SI result from coincident sources of stimulation in the fetal position, where the hands frequently touch the face, and the feet the genitalia. Computer modeling using a Hebbian variant of the self-organizing Kohonen net is consistent with this proposal. However, recent work reveals that the genital representation in SI for cutaneous sensations (as opposed to tumescence) is continuous with that of the lower trunk and thigh. This result, in conjunction with reports of separate face innervation and its earlier onset of sensory function, compared to that of the rest of the body, allows a reappraisal of homuncular organization. It is proposed that the somatosensory homunculus comprises two distinct somatotopic regions: the face representation and that of the rest of the body. Principles of self-organization do not account satisfactorily for the overall homuncular map. These results may serve to alert computational modelers that intrinsic developmental factors can override simple rules of plasticity.

Hybrid wavelet denoising procedure of discontinuous surfaces

In this study, the authors propose a method for recovering a two-dimensional surface (image) from noisy observations containing significant jumps and discontinuities. The proposed procedure, termed as the segmented polynomial wavelet regression (SPWR) algorithm, combines wavelet regression with polynomial extrapolation and segmentation procedures. The bias that might occur on the discontinuous surface is alleviated through a segmentation process, and at the same time, inhomogeneous multi-scale features of the surface are efficiently treated by wavelet regression. The SPWR algorithm enjoys all the benefits of wavelet regression by implicitly detecting the discontinuities, and it is fast and easy to implement. Through a simulation study, it is demonstrated that the proposed method can produce substantially effective results.

Rules and Discretion in the Evaluation of Students and Schools: The Case of the New York Regents Examinations

The challenge of designing effective performance measurement and incentives is a general one in economic settings where behavior and outcomes are not easily observable. These issues are particularly prominent in education where, over the last two decades, test-based accountability systems for schools and students have proliferated. In this study, we present evidence that the design and decentralized, school-based scoring of New York’s high-stakes Regents Examinations have led to pervasive manipulation of student test scores that are just below performance thresholds. Specifically, we document statistically significant discontinuities in the distributions of subject-specific Regent scores that align with the cut scores used to determine both student eligibility to graduate and school accountability. Our results suggest that roughly 3 to 5 percent of the exam scores that qualified for a high school diploma actually had performance below the state requirements. Using multiple sources of data, we present evidence that score manipulation is driven by local teachers’ desire to help their students avoid sanctions associated with failure to meet exam standards, not the recent creation of school accountability systems. We also provide some evidence that variation in the extent of manipulation across schools tends to favor traditionally disadvantaged student groups.

New insights into the reading of Paleozoic plant fossil record discontinuities

Studying the discontinuity patterns of Paleozoic vascular plants provides a global vision of these key events from the multivariate methods viewpoint. Non-metric multidimensional scaling, detrended correspondence analysis and cluster analysis have been employed together with a set of diversity and abundance measures and an evaluation of the geologic constraints from the plant fossil record data. The results reveal four clear significant discontinuities in terms of taxonomic composition and record representativeness during the early-middle Devonian, Devonian–Carboniferous, Mississippian–Pennsylvanian and early-late Permian. Due to the controversial character of the plant fossil record data and the effect of mass extinction events, the results can be explained in taxonomic turnover and ecological reorganisation terms which emphasise the crucial role of the geologic constrains in paleobiological inference.

Sedimentation and erosion processes in Middle to Late Pleistocene sequences exposed in the brickyard of Langenlois/Lower Austria

The correlation of sedimentary and pedogenetic processes in Lower Austria is difficult due to significant discontinuities and local variability in soil formation. This hampers landscape reconstruction at a regional scale. However, at a local scale distinct landscape formation processes represented by a shift from fluvial to aeolian deposition can be observed in the brickyard of Langenlois, Lower Austria. Sedimentological and mineralogical analyses in combination with palaeontological finds suggest that the fluvial deposition took place during the Middle Pleistocene. This attribution is confirmed by infra-red stimulated luminescence (IRSL) dating, which gives a minimum age of 300 ka for the palaeosurface on which the fluvial sediments were deposited. This is consistent with a small faunal assemblage including Stephanorhinus sp., Dama sp. and an alcine cervid. Such a fauna is previously unknown in Austria; it indicates a Middle Pleistocene interglacial period. The low degree of weathering as well as Cryosols found in the loess sequence point to loess accumulation during the Last Glacial; the dating results (35–55 ka) indicate prolonged loess deposition. No signs of pedogenesis could be found; this is surprising because in other areas this period is known for weak soil development. The lack of soil formation seems to be specific to the western part of Lower Austria, as is the complete erosion of the last glacial maximum (LGM) loess, which can not be found at Langenlois.

Introduction

By any measure, China's economic reform is of world-historical significance. While acknowledging the remarkable achievements China has made over the past thirty years, this introductory essay foregrounds some of the major challenges and problems China faces. Since the open-door policy was formally adopted in 1978, the country has been undergoing radical sociohistorical transformations that have created not only unprecedented wealth, new freedoms, and possibilities, but also widespread and significant inconsistencies and discontinuities that characterize the everyday life of China at the present moment. Is China's substantially marketized economy sufficient evidence of its abandonment of socialism? Is it a socialist market economy or marketized socialism? Is it a socialist state with “Chinese characteristics” or one without socialism? Would the continuation of economic reform lead to democratization? Thirty years after the reform, China has emerged as a site of paradoxes and contradictions. Contemporary China cannot be fully understood unless some of its most significant new features are identified, analyzed, and comprehended; but our attempt to understand what is unfolding in China requires an acknowledgment of the inadequacies of the accepted views and formulations about the country. By foregrounding some of those problems that this special issue of boundary 2 seeks to identify, analyze, and understand, the introduction urges for the need to move beyond the existing theoretical paradigms and categorizations for describing China's political and social formations, and to develop a more nuanced critical language for the complexities of contemporary Chinese society.

From Nazism to communism: German schoolteachers under two dictatorships

Tracing teachers' experiences in the Third Reich and East Germany, Charles Lansing analyzes developments in education of crucial importance to both dictatorships. Lansing uses the town of Brandenburg an der Havel as a case study to examine ideological reeducation projects requiring the full mobilization of the schools and the active participation of a transformed teaching staff. Although lesson plans were easily changed, skilled teachers were neither quickly made nor easily substituted. The men and women charged in the postwar era with educating a new 'antifascist' generation were, to a surprising degree, the same individuals who had worked to 'Nazify' pupils in the Third Reich. But significant discontinuities existed as well, especially regarding the teachers' professional self-understanding and attitudes toward the state-sanctioned teachers' union. The mixture of continuities and discontinuities helped to stabilize the early GDR as it faced its first major crisis in the uprising of June 17, 1953. This uniquely comparative work sheds new light on an essential story as it reconceptualizes the traditional periodization of postwar German and European history.

Western Palaearctic phylogeography of an inquiline oak gall wasp, Synergus umbraculus

Insect-induced galls on plants comprise species-rich but self-contained communities of herbivores and natural enemies. In the present study, we focus on galls induced by cynipid gall wasps on oaks, and on the least-known trophic level that these galls contain: inquilines. These insects, also cynipids, feed on gall tissue and are an abundant but taxonomically poorly understood part of an otherwise well-studied system. We used DNA sequence data to examine spatial patterns in the genetic diversity of Synergus umbraculus Olivier 1791 (Hymenoptera: Cynipidae: Synergini), a widespread species attacking many host galls across the Western Palaearctic. Analysis of 239 cytochrome b sequences revealed eight haplogroups showing significant phylogeographic pattern across the Western Palaearctic, corresponding to putative glacial refugia in Iberia, Central Europe, Turkey, and Iran. There were significant genetic discontinuities across the Pyrenees and the Anatolian diagonal but no impact of the Alps, suggesting that significant discontinuities have biotic rather than physical causes. Detailed analysis of sites in the Carpathian Basin reveal a high diversity and low spatial structure, and identify Central Europe as the source of colonists for Quaternary colonization of Germany, France, and Britain. We found no evidence for host-associated differentiation of S. umbraculus lineages associated with the most common cynipid host galls, suggesting frequent shifts within the host gall assemblage by inquiline lineages. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102, 750–764.

The breakdown of Kohn's theorem in few-electron parabolic quantum dots doped with a single magnetic impurity Mn2+

The cyclotron resonance (CR) absorption spectrum is calculated for a II-VI parabolic quantum dot (QD) containing few electrons and a single magnetic dopant (Mn2+). We find that Kohn's theorem no longer holds for this system and that the CR spectrum depends on the number of electrons inside the QD. The electron-Mn-ion interaction strength can be tuned for example by the magnetic field and by moving the Mn-ion to different positions inside the QD. We demonstrate that due to the presence of the Mn-ion the relative motion of the electrons couple with their center-of-mass motion through the electron-Mn-ion spin-spin exchange term resulting in an electron-electron interaction dependence of the magneto-optical absorption spectrum. At the ferromagnetic-antiferromagnetic transition we observe significant discontinuities in the CR lines.

Unraveling the tilting history of the submerged reefs surrounding Oahu and the Maui‐Nui Complex, Hawaii

There is considerable uncertainty concerning the history of lithospheric flexure of Oahu and the Maui‐Nui Complex associated with the Hawaiian hot spot. Previous reconstructions based on models and sparse observational data place the zone of maximum uplift (forebulge) either under Oahu or between Oahu and Molokai. To address this issue we have compiled and analyzed all existing and new high‐resolution multibeam bathymetry, dive observations, and chronologic data from submerged terraces in the region. We have identified 89 separate submarine terraces and mapped their distribution across the volcanic flanks of Oahu and the Maui‐Nui Complex. These data are used to systematically measure the direction and amplitude of terrace tilting within the Maui‐Nui Complex and to provide new constraints on lithospheric flexure associated with volcanic loading at the hot spot. The terraces are divided into six separate geographic regions (Oahu, Molokai, Penguin Bank, Lanai, Maui, and East Maui) defined by significant discontinuities in either terrace morphology or depth. Following the sequential development of new substrate as the new volcanoes formed throughout the development of the MNC, 18 new and 51 published 87Sr/86Sr isotopic ages show that the terraces in these regions were also initiated at different times, and the tilting data show that they also responded to lithospheric flexure independently. The general pattern of terrace tilting records the plate's response to lithospheric flexure with each region continually tilting toward the zone of maximum subsidence since their formation. Our individual tilt calculations are based on the most complete and highest‐resolution bathymetric data available, and they show that plate response to volcanic loading is a gradual process. Finally, we demonstrate that the shallowest terraces we identified in the Oahu and Molokai regions tilt toward the north, away from the current zone of maximum subsidence, indicating that these regions have recently passed the zone of maximum uplift. We compare our results with two separate published numerical models and differentiate between these, resolving a long‐standing uncertainty in the position of the forebulge.

Spatial-gradient-local-inhomogeneity: an efficient image-denoising prior

We provide an efficient image-denoising prior, spatial-gradient-local-inhomogeneity (SGLI), which can be successfully applied to image reconstruction. The SGLI prior employs two complementary discontinuity measures: spatial gradient and local inhomogeneity. The spatial gradient measures effectively preserves strong edge components of images, while the local inhomogeneity measure successfully detects locations of the significant discontinuities considering uniformity of small regions. The two complementary measures are elaborately combined into the SGLI prior for image denoising. Thus, the SGLI prior effectively preserves feature components such as edges and textures of images while reducing noise. Comparative results indicate that the proposed SGLI prior is very effective in dealing with the image denoising problem from corrupted images.