Distribution by Scientific Domains
Distribution within Medical Sciences

Kinds of Margin

  • active continental margin
  • anal margin
  • anterior margin
  • atlantic margin
  • basin margin
  • cervical margin
  • channel margin
  • circumferential resection margin
  • clear margin
  • clear surgical margin
  • coastal margin
  • continental margin
  • convergent margin
  • deep margin
  • delay margin
  • distal margin
  • eastern margin
  • error margin
  • excision margin
  • extensive margin
  • field margin
  • free margin
  • gingival margin
  • gross margin
  • high safety margin
  • ice margin
  • inner margin
  • intensive margin
  • interest margin
  • involved margin
  • irregular margin
  • joint margin
  • lateral margin
  • leaf margin
  • lid margin
  • negative margin
  • negative surgical margin
  • non-inferiority margin
  • noninferiority margin
  • northeastern margin
  • northern margin
  • occlusal margin
  • operating margin
  • orbital margin
  • passive continental margin
  • passive margin
  • positive margin
  • positive surgical margin
  • posterior margin
  • price-cost margin
  • profit margin
  • range margin
  • resection margin
  • retinal margin
  • robust stability margin
  • safety margin
  • section margin
  • shelf margin
  • southeastern margin
  • southern margin
  • stability margin
  • surgical margin
  • therapeutic margin
  • tissue margin
  • tumor margin
  • tumor-free margin
  • tumour margin
  • tumour-free margin
  • ulcer margin
  • valve margin
  • western margin
  • wide margin
  • wound margin

  • Terms modified by Margin

  • margin control
  • margin involvement
  • margin positivity
  • margin requirement
  • margin setting
  • margin status

  • Selected Abstracts


    ABSTRACT. The origin of two ridges on the eastern slopes of Mt Allen, southern Stewart Island, has remained equivocal, with differences of opinion over the exact process-mechanisms of formation. A variety of approaches was used to test a number of possible hypotheses about the origin of the ridges. These include topographic and spatial positioning, geomorphology, sedimentology and palaeoclimatological extrapolations to reconstruct two small former cirque glaciers with equilibrium line altitudes (ELAs) of c. 600 m. It would appear the two ridges reflect a glacial origin, the glaciers interpreted as forming during the Last Glacial Maximum (LGM) in New Zealand. Whilst glaciation during this time (18,19 ka) was extensive in the Southern Alps, the restricted nature of glaciation on Mt Allen suggests the low altitude restricted glaciation to niche sites on the lee side of upland areas. [source]


    ABSTRACT. Geomorphological and sedimentological evidence of former glaciation in the Bizzle valley in the Cheviot Hills of northern England and southern Scotland was used to reconstruct the dimensions of a small topographically constrained glacier with an equilibrium line altitude (ELA) of 535 m. This was interpreted as having formed during Younger Dryas cooling; this is the only glacier to have been described from the area and is the most easterly site of Younger Dryas glaciation in the British Isles. Whilst glaciation at this time was extensive in the Lake District to the southwest, the restricted nature of Cheviot ice cover suggests that a steep west,east precipitation gradient existed in this region during the Younger Dryas. [source]


    This paper allows for endogenous costs in the estimation of price cost margins. In particular, we estimate price-cost margins when firms bargain over wages. We extent the standard two-equation set-up (demand and first-order condition in the product market) to include a third equation, which is derived from bargaining over wages. In this way, price-cost margins are determined by wages and vice versa. We implement the model using data for eight European airlines from 1976,1994, and show that the treatment of endogenous costs has important implications for the measurement of price-cost margins and the assessment of market power. Our main result is that observed prices in Europe are virtually identical to monopoly prices, even though observed margins are consistent with Nash behavior. Apparently, costs had been inflated to the point that the European consumers were faced with a de facto monopoly prices. [source]


    ANZ JOURNAL OF SURGERY, Issue 12 2006
    Kok-Yang Tan
    Background: Adequacy of margins is important for local recurrence control in breast-conserving surgery for breast cancer. This study aims to compare the accuracy of intraoperative specimen ultrasonography (IOUS) and specimen mammography in the prediction of achieving adequate histologically tumour-free margins during breast-conserving surgery. Methods: Between March 2003 and September 2004, a prospective study was carried out on 25 patients who underwent breast-conserving surgery. After wide excision, IOUS and specimen mammography were used to assess adequacy of margins. Further surgery was undertaken when either method showed an inadequate margin. The margins were assessed histologically and correlated with IOUS and mammographic findings. Results: Using IOUS alone, higher rates of histologically tumour-free margins were achieved compared with mammography alone. Combined IOUS and mammography achieved similar or slightly higher rates of histologically tumour-free margins compared with IOUS alone. If the margin measured on IOUS is twice the desired histological margin, this will result in achieving a histologically tumour-free rate of >90%. Associated ductal carcinoma in situ was the only significant factor found to decrease the rate of achieving adequate margins. Conclusion: Intraoperative specimen ultrasonography is useful in predicting histologically tumour-free margins during breast conserving surgery for cancer. [source]


    ANZ JOURNAL OF SURGERY, Issue 7 2006
    Paul R. B. Kitchen
    Background: In situ disease surrounding invasive tumours is an important consideration in the management of patients with early breast cancer. This study of screen-detected breast cancers assessed the influence of in situ disease including an extensive in situ component (defined as ductal carcinoma in situ involving more than 25% of the area within the invasive tumour) on surgical management, local recurrence and survival of a group of patients. Methods: A total of 595 cases of invasive breast cancer detected at St Vincent's BreastScreen were retrospectively reviewed to determine presence and extent of in situ disease, the surgical procedure and adequacy of excision. Outcome was examined in a cohort of 126 cases. Results: A total of 438 (74%) patients had in situ foci in or around the invasive tumour and 107 (18%) were defined as extensive in situ component (EIC)-positive. The initial procedure was mastectomy in 20% of the cases and breast-conserving surgery in 80% including 18% who underwent further surgery. Re-excision (P = 0.02) or mastectomy (P = 0.01) was more often required in patients with EIC. After definitive local excision, margins were close or involved with invasive disease in 3% but the patients with EIC were more likely to have margins close or involved with in situ disease (16 vs 2%; P = 0.001). There were seven deaths and one local invasive recurrence in the follow-up group and none of the deaths were in patients who were EIC-positive. Conclusions: EIC predicts for a higher rate of re-excision and/or mastectomy. For patients with EIC, there is an acceptably low risk of local recurrence if margins are clear. [source]


    ANZ JOURNAL OF SURGERY, Issue 3 2006
    Peter F. M. Choong
    No abstract is available for this article. [source]

    Crescent Versus Rectangle: Is It a True Negative Margin in Second and Subsequent Stages of Mohs Surgery?

    BACKGROUND The hallmark of Mohs micrographic surgery is using tangential tissue sections that theoretically allow 100% of the tissue margin to be examined, but when taking additional layers for second and subsequent Mohs stages, no detailed methods have been described to ensure that 100% of the tissue margins are analyzed. METHOD A rectangular or a crescent-shaped layer is often used to take second and subsequent stages. Here we compare the two techniques for their theoretic advantages and disadvantages. SUMMARY The advantage of the rectangular shape has been ease of processing, as well as built in vertical "nicks" that automatically mark the border of the tissue removed, but the rectangular layer may not provide 100% evaluation of the tumor margin because the vertical edges of the rectangular layer are not always completely analyzed, and thus tumor cells cannot be visualized in the vertical margins of these layers. This might result in a false-negative margin reading, which can be avoided by using the crescent layer. CONCLUSION We propose taking second and subsequent Mohs layers with only a crescent shape, which allows true 100% tissue margin assessment. The authors have indicated no significant interest with commercial supporters. [source]

    Squamous Cell Carcinoma of the Anal Margin with Pruritus Ani of Long Duration

    Yoshihiro Handa MD
    BACKGROUND. Anal margin is an unusual location for squamous cell carcinoma (SCC). On rare occasions, anal margin carcinoma is the cause of pruritus ani. OBJECTIVE. To describe a case of SCC of the anal margin with pruritus ani of long duration. RESULTS. A 52-year-old man had been aware of perianal itching for over 10 years. Examination of the perianal area revealed a reddish, eroded, hard nodule that was 2.0×1.5 ×0.3 cm in size located in the 3 o'clock position. The histopathologic diagnosis was well-differentiated SCC. The nodule was totally excised with a 1-cm margin. No recurrence or metastases were observed for 7 months. CONCLUSION. When pruritus ani does not respond to conservative therapy and when symptoms have existed for a long time, we should suspect the presence of malignancy. [source]

    External Imbalances and the Extensive Margin of Trade

    ECONOMIC NOTES, Issue 3 2008
    Vahagn Galstyan
    We quantify the role of the extensive margin in the recent trade dynamics of selected countries that are running large and persistent trade imbalances. We find that the role of the extensive margin is quite substantial, although it varies in significance across the countries in the sample. Finally, we highlight differences in behaviour between the fixed-varieties and varieties-adjusted terms of trade. [source]

    Direct in situ detection of cells in deep-sea sediment cores from the Peru Margin (ODP Leg 201, Site 1229)

    GEOBIOLOGY, Issue 4 2004
    ABSTRACT Microbiological investigations of deep-sea sediments recovered from the Peru Margin during the ODP Leg 201 (Hole 1229A, 1,110 mbsf) demonstrated that microoganisms were a consistent component throughout the profile. Optimization of the dilution factor and DAPI-staining procedures for direct cell counts allowed the determination of the abundance of the entire microbial community, which was about 108 cells per g dry sediment. Microbial diversity in discrete samples taken from the 110-m profile was analysed using horseradish-peroxydase-rRNA-probes. In general, the majority of the detected cells belonged to the Eubacteria kingdom with a dominance of sulphate-reducing bacteria. The composition of the suflate-reducing community varied with depth. Desulfobacteriaceae were dominant in the uppermost sulphate-reducing zone and Desulfovibrionaceae at deeper depths in the upward diffusing sulphate-rich brines. Both sulphate-reducing groups were also detected in the methanogenic zone. Similarly, Archaea were detected throughout the profile, not only in the methanogenic zone but also in the upper and lower sulphate-reducing zones. [source]

    Landscape and Coast Development of A Lowland Fjord Margin Following Deglaciation, East Greenland

    Louise Hansen
    The landscapes of western Jameson Land bordering Hall Bredning fjord comprise upper river basins, glacial landscapes, lower river basins and a near-shore zone. The upper river basins are incised into bedrock and display no cover of young sediments whilst the glacial landscapes, located closer to the coast, are dominated by Pleistocene deposits and an irregular topography with hills and ridges. The lower river basins, dissecting the glacial landscapes, are connected to the upper river basins and contain well-defined Holocene delta terraces. The near-shore zone, which includes the present coast, displays a few raised shorelines. Geomorphological observations combined with stratigraphic work and 14C dates provide a chronological framework for the development of landscape and shoreline, as presented by a four-stage reconstruction. The first stage covers the deglaciation of western Jameson Land at the Weichselian-Holocene transition after a collapse of the main fjord glacier in Hall Bredning. The sea inundated the low-lying areas on Jameson Land forming small side-entry fjord basins that possibly follow the track of older valleys. This was followed by a second stage, the paraglacial period, when large meltwater production and sediment transport resulted in a fast infilling of the side-entry fjord basins by deltas. These are now exposed in terraces in the lower river basins at 70,80 m a.s.l. During a third stage, the relaxation period, fluvial activity decreased and the land surface was increasingly occupied by a cover of tundra vegetation. A glacio-isostatic rebound resulted in a relative sea level fall and fluvial incision. During stages two and three the coast was exposed to shallow marine processes that aided the alignment of the coast. Stages one to three presumably lasted for less than 2000 years. During stage four, the stable period, lasting for several thousand years till the present, there were minor adjustments of shoreline and landscape. The four-step reconstruction describes the sedimentary response of a lowland fjord margin to dramatic changes in climate and sea level. The distribution of erosion and sedimentation during this development was mainly controlled by topography. The reconstruction of the latest environmental development of Jameson Land puts new light on Jameson Land's long and complex Quaternary stratigraphic record. The reconstruction may also be used as a model for the interpretation of deposits in similar areas elsewhere. [source]

    A quantitative study on the use of converted waves for sub-basalt imaging

    Peter Hanssen
    ABSTRACT The idea of imaging beneath a high-velocity layer using converted waves has been popular since 1990. Because these wave types have their maximum amplitudes at mid- to far-offsets, the search for pure P-waves at the highly multiple-contaminated near-offsets can be avoided. For the Atlantic Margin, with buried thin-layered basalts, our quantitative study shows that the initial single-layered approach is not viable. Even in an unrealistic ideal geological setting, the amplitude of the symmetrical PSP-mode is far too weak to be recognized on towed streamer data. Furthermore, in the far-offset window, where locally converted waves have their strongest amplitudes, there is a multitude of other reflections, refractions and interbedded multiples, which have similar moveouts and, often, higher amplitudes. Without the removal of these events, a reliable image of the subsurface cannot be produced. We show that even if this problem were solved, it would be far easier to use the P-wave reflection from beneath the basalt at near-offsets. Our study shows that this wave type is by far the strongest response. A borehole-derived model using a thin-layered basalt sequence reveals that the strongest locally converted wave has an asymmetrical path and is 10 times weaker. All our results indicate that the pure P-modes provide the best chance of imaging sub-basalt sedimentary interfaces. [source]

    Identifying the Relative Contributions of Rac1 and Rac2 to Osteoclastogenesis,,

    Yongqiang Wang
    Abstract Rac small GTPases may play an important regulatory role in osteoclastogenesis. Our in vitro and in vivo results show that both Rac1 and Rac2 are required for optimal osteoclast differentiation, but Rac1 is more critical. Rac1 is the key Rac isoform responsible for regulating ROS generation and the actin cytoskeleton during the multiple stages of osteoclast differentiation. Introduction: Recent evidence suggests that the Rac small GTPases may play an important regulatory role in osteoclastogenesis. This finding is important because bisphosphonates may regulate their antiresorptive/antiosteoclast effects through the modification of Rho family of small GTPases. Materials and Methods: To elucidate the specific roles of the Rac1 and Rac2 isoforms during osteoclastogenesis, we used mice deficient in Rac1, Rac2, or both Rac1 and Rac2 in monocyte/osteoclast precursors. Macrophage-colony stimulating factor (M-CSF), and RANKL-mediated osteoclastogenesis in vitro was studied by using bone marrow-derived mononucleated preosteoclast precursors (MOPs). The expression of osteoclast-specific markers was examined using quantitative real-time PCR and Western blot analysis. Free actin barbed ends in bone marrow MOPs after M-CSF stimulation was determined. The ability of MOPs to migrate toward M-CSF was assayed using Boyden chambers. Margin spreading on heparin sulfate-coated glass and RANKL-induced reactive oxygen species generation were also performed. Functional assays of in vitro-generated osteoclasts were ascertained using dentine sections from narwal tusks. Osteoclast levels in vivo were counted in TRACP and immunohistochemically stained distal tibial sections. In vivo microarchitexture of lumbar vertebrate was examined using ,CT 3D imaging and analysis. Results: We show here that, although both Rac isoforms are required for normal osteoclast differentiation, Rac1 deletion results in a more profound reduction in osteoclast formation in vitro because of its regulatory role in pre-osteoclast M-CSF-mediated chemotaxis and actin assembly and RANKL-mediated reactive oxygen species generation. This Rac1 cellular defect also manifests at the tissue level with increased trabecular bone volume and trabeculae number compared with wildtype and Rac2-null mice. This unique mouse model has shown for the first time that Rac1 and Rac2 play different and nonoverlapping roles during osteoclastogenesis and will be useful for identifying the key roles played by these two proteins during the multiple stages of osteoclast differentiation. Conclusions: Rac1 and Rac2 play different and nonoverlapping roles during osteoclastogenesis. This model showed that Rac1 is the key Rac isoform responsible for regulating ROS generation and the actin cytoskeleton during the multiple stages of osteoclast differentiation. [source]

    An Analysis of the Effect of a Vent Hole on Excess Cement Expressed at the Crown,Abutment Margin for Cement-Retained Implant Crowns

    Dipan Patel BDS
    Abstract Purpose: The labial margins of anterior implant-retained crowns are often positioned subgingivally for a superior esthetic appearance. One of the consequences of subgingival margins is the increased risk of leaving excess cement behind following cementation. This can lead to potential problems, including peri-implant inflammation, soft tissue swelling, soreness, bleeding or suppuration on probing, and bone loss. The purpose of this laboratory study was to investigate the effect of placement, location, and diameter of a vent hole on the amount of cement being expressed at the margin of an anterior implant abutment-retained crown. Materials and Methods: Three implant crown copings were fabricated to fit on the same custom abutment. Three vent diameters (0.75, 1.25, and 1.65 mm) and three locations on the palatal surface of the coping (cervico-palatally, mid-palatally, inciso-palatally) were chosen for vent hole placement. For each test, the coping was cemented onto the abutment under standardized conditions. A preweighed thin coating of cement was applied to the fit surface of the coping. The amount of cement expressed at the margin and vent hole was measured by weight and calculated as a proportion of the amount of cement placed in the coping before seating. The procedure was completed 15 times for each variable. The results were statistically analyzed using univariate ANOVA with post hoc Bonferroni-adjusted independent samples t -tests. Results: The presence of a vent hole influenced the proportion of cement expressed at the coping margin (p < 0.05). The location of a vent hole influenced the proportion of cement expressed at the coping margin (p < 0.05), with the exception of the mid-palatal and inciso-palatal positioning where there was no significant difference (p= 0.61) between groups. The diameter of the vent hole did not significantly influence the proportion of cement expressed at the coping margin (p= 0.096). Conclusions: When using anterior cement-retained implant crowns, the use of a 0.75-mm mid-palatal or inciso-palatal vent hole to minimize the amount of cement expressed at the margin during cementation should be considered. [source]

    The Cost of Flexibility at the Margin.

    LABOUR, Issue 4-5 2007
    Comparing the Wage Penalty for Fixed-term Contracts in Germany, Spain using Quantile Regression
    Using quantile regression we find that in West Germany the earnings of permanent and fixed-term workers are most similar among high earners and most dissimilar among low earners. In Spain, the wage penalty shows little variation across the distribution of wages. This pattern was also found for different occupational groups, although there are clear differences in the absolute wage penalty across occupations. In conclusion we caution against generalizing findings from Spain to other ,rigid' European labour markets. [source]

    Sedimentation record in the Konkan,Kerala Basin: implications for the evolution of the Western Ghats and the Western Indian passive margin

    BASIN RESEARCH, Issue 1 2008
    D. Campanile
    ABSTRACT The Konkan and Kerala Basins constitute a major depocentre for sediment from the onshore hinterland of Western India and as such provide a valuable record of the timing and magnitude of Cenozoic denudation along the continental margin. This paper presents an analysis of sedimentation in the Konkan,Kerala Basin, coupled with a mass balance study, and numerical modelling of flexural responses to onshore denudational unloading and offshore sediment loading in order to test competing conceptual models for the development of high-elevation passive margins. The Konkan,Kerala Basin contains an estimated 109 000 km3 of Cenozoic clastic sediment, a volume difficult to reconcile with the denudation of a downwarped rift flank onshore, and more consistent with denudation of an elevated rift flank. We infer from modelling of the isostatic response of the lithosphere to sediment loading offshore and denudation onshore infer that flexure is an important component in the development of the Western Indian Margin. There is evidence for two major pulses in sedimentation: an early phase in the Palaeocene, and a second beginning in the Pliocene. The Palaeocene increase in sedimentation can be interpreted in terms of a denudational response to the rifting between India and the Seychelles, whereas the mechanism responsible for the Pliocene pulse is more enigmatic. [source]

    3D seismic analysis of slope-confined canyons from the Plio,Pleistocene of the Ebro Continental Margin (Western Mediterranean)

    BASIN RESEARCH, Issue 1 2005
    Claudia Bertoni
    This paper documents the importance of three-dimensional (3D) seismic data for integrated stratigraphic,morphological analysis of slope systems. Furthermore, it contributes to the general understanding of the evolutionary mechanisms of slope-confined submarine canyons on continental margins and their significance in a sequence stratigraphic framework. Recently acquired 3D seismic data from the Ebro Continental Margin (Western Mediterranean) have been used to study a series of remarkably well-imaged submarine canyons in the Plio-Pleistocene succession. Detailed mapping shows that these canyons are restricted to the slope, and thus can be compared with slope-confined canyons observed on the present day seabed of many continental margins. The slope-confined canyons are typically 0.5,2 km wide, 10,15 km long, and incise more than 50 m into the slope units. Their most striking characteristic is an upslope branching geometry in the head region involving up to three orders of bifurcation, with downslope development of a single incisional axis. The submarine canyons are characterized by a nested stacking pattern, undergoing alternating phases of cutting and filling. Limited parts of the upper and middle slope remain outside the canyon system, confined in sharp depositional ridges. The canyons are observed on closely spaced surfaces and exhibit a geometry that allowed the construction and discussion of a local sequence stratigraphic model for their evolution. In general, active incision of the canyons is observed at times throughout almost the entire cycle of base-level change. However, erosional activity is more significant during the later stages of the relative sea level rise and the entire falling stage, with the timing of maximum erosion observed at the end of the cycle. The minimum erosional activity of the canyons is linked instead to the earliest part of the relative sea level rise. [source]

    Neoproterozoic Mafic Dykes and Basalts in the Southern Margin of Tarim, Northwest China: Age, Geochemistry and Geodynamic Implications

    Chuanlin ZHANG
    Abstract: Neoproterozoic rifting-related mafic igneous rocks are widely distributed both in the northern and southern margins of the Tarim Block, NW China. Here we report the geochronology and systematic whole-rock geochemistry of the Neoproterozoic mafic dykes and basalts along the southern margin of Tarim. Our zircon U-Pb age, in combination with stratigraphic constraint on their emplacement ages, indicates that the mafic dykes were crystallized at ca. 802 Ma, and the basalt, possibly coeval with the ca. 740 Ma volcanic rocks in Quruqtagh in the northern margin of Tarim. Elemental and Nd isotope geochemistry of the mafic dykes and basalts suggest that their primitive magma was derived from asthenospheric mantle (OIB-like) and lithospheric mantle respectively, with variable assimilation of crustal materials. Integrating the data supplied in the present study and that reported previously in the northern margin of Tarim, we recognize two types of mantle sources of the Neoproterozoic mafic igneous rocks in Tarim, namely the matasomatized subcontinental lithospheric mantle (SCLM) in the northern margin and the long-term enriched lithospheric mantle and asthenospheric mantle in the southern margin. A comprehensive synthesis of the Neoproterozoic igneous rocks throughout the Tarim Block led to the recognition of two major episodes of Neoproterozoic igneous activities at ca. 820,800 Ma and ca. 780,740 Ma, respectively. These two episodes of igneous activities were concurrent with those in many other Rodinian continents and were most likely related to mantle plume activities during the break-up of the Rodinia. [source]

    Archean Basement and a Paleoproterozoic Collision Orogen in the Huoqiu Area at the Southeastern Margin of North China Craton: Evidence from Sensitive High Resolution Ion Micro-Probe U-Pb Zircon Geochronology

    Yusheng WAN
    Abstract: This paper reports sensitive high resolution ion micro-probe U-Pb zircon ages for the "Huoqiu Group" and granitoids of the Early Precambrian basement in the Huoqiu area, southeastern margin of the North China Craton. The "Huoqiu Group" is similar in rock association and metamorphism to the khondalite series, apart from it containing considerable amounts of banded iron formation. All detrital zircons from the "Huoqiu Group" meta-sedimentary rocks are 3.0 Ga and 2.75 Ga, without any 2.5 Ga and younger ones, as is commonly found in Paleoproterozoic khondalite series in other areas of the North China Craton. In the Huoqiu area, 2.75 Ga and 2.56 Ga granitoids have also been identified. This basement assemblage underwent strong metamorphism during the late Paleoproterozoic (, 1.84 Ga) tectonothermal event that is widely developed in the North China Craton. Thus the formation time of the "Huoqiu Group" can be constrained between 2.75 and 1.84 Ga in terms of detrital and metamorphic zircon ages. It is considered, combined with regional data, that there may be a Paleoproterozoic collision orogen extending in a NWW,SEE direction to the southern margin of the North China Craton. [source]

    Tectonic Evolution of the Tianhuan Depression and the Western Margin of the Late Triassic Ordos

    LI Xiangbo
    Abstract: The Ordos Basin is one of the most important oil and gas basins in China. Based on surface outcrop, key exploratory wells and seismic reflection data and by using the technology of "prototype basin recovery", seismic profile "layer flattening" and "restoration of balanced section", and other methods, the sedimentary boundary, structure and the evolution history of the Tianhuan depression on the western margin of the Ordos Basin are reestablished. The following results have been obtained. (1) The west boundary of the Late Triassic Ordos Basin was far beyond the scope of the current basin. The basin is connected with the Late Triassic Hexi Corridor Basin, and its western margin did not have tectonic characteristics of a foreland basin. (2) The Tianhuan depression was first formed in the Late Jurassic. At the late stage it was impacted by the late Yanshanian and Himalayan tectonic movement and the depression axis gradually moved eastwards to the present location with a cumulative migration distance of ,30 km. (3) Eastward migration of the depression axis caused adjustment and even destruction of the originally formed oil and gas reservoirs, so that oil and gas remigrated and aggregated, resulting in secondary structural reservoirs formed at high positions on the western flank of the depression. [source]

    Petroleum System of the Sufyan Depression at the Eastern Margin of a Huge Strike-slip Fault Zone in Central Africa

    ZHANG Yamin
    Abstract: The present paper mainly studies the petroleum system of the Sufyan Depression in the Muglad Basin of central Africa and analyzes its control of hydrocarbon accumulation. On the basis of comprehensive analysis of effective source rock, reservoir bed types and source,reservoir,seal assemblages, petroleum system theory has been used to classify the petroleum system of the Sufyan Depression. Vertically, the Sufyan Depression consists of two subsystems. One is an Abu Gabra subsystem as a self generating, accumulating and sealing assemblage. The other subsystem is composed of an Abu Gabra source rock, Bentiu channel sandstone reservoir and Darfur group shale seal, which is a prolific assemblage in this area. Laterally, the Sufyan Depression is divided into eastern and western parts with separate hydrocarbon generation centers more than 10 000 m deep. The potential of the petroleum system is tremendous. Recently, there has been a great breakthrough in exploration. The Sufyan C-1 well drilled in the central structural belt obtained high-yielding oil flow exceeding 100 tons per day and controlled geologic reserves of tens of millions of tons. The total resource potential of the Sufyan Depression is considerable. The central structural belt is most favorable as an exploration and development prospect. [source]

    Petrogenesis of Volcanic Rocks in the Khabr-Marvast Tectonized Ophiolite: Evidence for Subduction Processes in the South-Western Margin of Central Iranian Microcontinent

    Abstract: The Late Cretaceous Khabr,Marvast tectonized ophiolite is located in the middle part of the Nain,Baft ophiolite belt, at the south-western edge of the central Iranian microcontinent. Although all the volcanic rocks in the study area indicate subduction-related magmatism (e.g. high LILE (large ion lithophile elements) / HFSE (high field strenght elements) ratios and negative anomalies in Nb and Ta), geological and geochemical data clearly distinguish two distinct groups of volcanic rocks in the tectonized association: (1) group 1 is comprised of hyaloclastic breccias, basaltic pillow lavas, and andesite sheet flows. These rocks represent the Nain,Baft oceanic crust; and (2) group 2 is alkaline lavas from the top section of the ophiolite suite. These lavas show shoshonite affinity, but do not support the propensity of ophiolite. [source]

    Dextral-Slip Thrust Faulting and Seismic Events of the Ms 8.0 Wenchuan Earthquake, Longmenshan Mountains, Eastern Margin of the Tibetan Plateau

    Zhenhan WU
    Abstract: Dextral-slip thrust movement of the Songpan-Garzê terrain over the Sichuan block caused the Ms 8.0 Wenchuan earthquake of May 12, 2008 and offset the Central Longmenshan Fault (CLF) along a distance of ,250 km. Displacement along the CLF changes from Yingxiu to Qingchuan. The total oblique slip of up to 7.6 m in Yingxiu near the epicenter of the earthquake, decreases northeastward to 5.3 m, 6.6 m, 4.4 m, 2.5 m and 1.1 m in Hongkou, Beichuan, Pingtong, Nanba and Qingchuan, respectively. This offset apparently occurred during a sequence of four reported seismic events, EQ1,EQ4, which were identified by seismic inversion of the source mechanism. These events occurred in rapid succession as the fault break propagated northeastward during the earthquake. Variations in the plunge of slickensides along the CLF appear to match these events. The Mw 7.5 EQ1 event occurred during the first 0,10 s along the Yingxiu-Hongkou section of the CLF and is characterized by 1.7 m vertical slip and vertical slickensides. The Mw 8.0 EQ2 event, which occurred during the next 10,42 s along the Yingxiu-Yanziyan section of the CLF, is marked by major dextral-slip with minor thrust and slickensides plunging 25°,35° southwestward. The Mw 7.5 EQ3 event occurred during the following 42,60 s and resulted in dextral-slip and slickensides plunging 10° southwestward in Beichuan and plunging 73° southwestward in Hongkou. The Mw 7.7 EQ4 event, which occurred during the final 60,95 s along the Beichuan-Qingchuan section of the CLF, is characterized by nearly equal values of dextral and vertical slips with slickensides plunging 45°,50° southwestward. These seismic events match and evidently controlled the concentrations of landslide dams caused by the Wenchuan earthquake in Longmenshan Mountains. [source]

    Cenozoic Exhumation and Thrusting in the Northern Qilian Shan, Northeastern Margin of the Tibetan Plateau: Constraints from Sedimentological and Apatite Fission-Track Data

    Zhaojie GUO
    Abstract: The Qilian Shan lies along the northeastern edge of the Tibetan Plateau. To constrain its deformation history, we conducted integrated research on Mesozoic,Cenozoic stratigraphic sections in the Jiuxi Basin immediately north of the mountain range. Paleocurrent measurements, sandstone compositional data, and facies analysis of Cenozoic stratigraphic sections suggest that the Jiuxi Basin received sediments from the Altyn Tagh Range in the northwest, initially in the Oligocene (,33 Ma), depositing the Huoshaogou Formation in the northern part of the basin. Later, the source area of the Jiuxi Basin changed to the Qilian Shan in the south during Late Oligocene (,27 Ma), which led to the deposition of the Baiyanghe Formation. We suggest that uplift of the northern Qilian Shan induced by thrusting began no later than the Late Oligocene. Fission-track analysis of apatite from the Qilian Shan yields further information about the deformation history of the northern Qilain Shan and the Jiuxi Basin. It shows that a period of rapid cooling, interpreted as exhumation, initiated in the Oligocene. We suggest that this exhumation marked the initial uplift of the Qilian Shan resulting from the India,Asia collision. [source]

    Basin- and Mountain-Building Dynamic Model of "Ramping-Detachment-Compression" in the West Kunlun-Southern Tarim Basin Margin

    CUI Junwen
    Abstract: Analysis of the deformation structures in the West Kunlun-Tarim basin-range junction belt indicates that sediments in the southwestern Tarim depression were mainly derived from the West Kunlun Mountains and that with time the region of sedimentation extended progressively toward the north. Three north-underthrusting (subducting), steep-dipping, high-velocity zones (bodies) are recognized at depths, which correspond to the central West Kunlun junction belt (bounded by the Küda-Kaxtax fault on the north and Bulungkol-Kangxiwar fault on the south), Quanshuigou fault belt (whose eastward extension is the Jinshajiang fault belt) and Bangong Co-Nujiang fault belt. The geodynamic process of the basin-range junction belt generally proceeded as follows: centering around the magma source region (which largely corresponds with the Karatag terrane at the surface), the deep-seated material flowed and extended from below upward and to all sides, resulting in strong deformation (mainly extension) in the overlying lithosphere and even the upper mantle, appearance of extensional stress perpendicular to the strike of the orogenic belt in the thermal uplift region or at the top of the mantle diapir and localized thickening of the sedimentary cover (thermal subsidence in the upper crust). Three stages of the basin- and mountain-forming processes in the West Kunlun-southern Tarim basin margin may be summarized: (1) the stage of Late Jurassic-Early Cretaceous ramping-rapid uplift and rapid subsidence, when north-directed thrust propagation and south-directed intracontinental subduction, was the dominant mechanism for basin- and mountain-building processes; (2) the stage of Late Cretaceous-Paleogene deep-level detachment-slow uplift and homogeneous subsidence, when the dominant mechanism for the basin- and mountain-forming processes was detachment (subhorizontal north-directed deep-level ductile shear) and its resulting lateral propagation of deep material; and (3) the stage of Neogene-present compression-rapid uplift and strong subsidence, when the basin- and mountain-forming processes were simultaneously controlled by north-vergent thrust propagation and compression. The authors summarize the processes as the "ramping-detachment-compression basin- and mountain-forming dynamic model". The basin-range tectonics was initiated in the Late Jurassic, the Miocene-Pliocene were a major transition period for the basin- and mountain-forming mechanism and the terminal early Pleistocene tectonic movement in the main laid a foundation for the basin-and-mountain tectonic framework in the West Kunlun-southern Tarim basin margin. [source]

    Reading The Bible From the Margins by Miguel De La Torre

    Article first published online: 23 MAY 200
    Reviewed by Leslie Houlden, p.4 Responce by Miguel De La Torre, p.8 [source]

    Test Characteristics of High-Resolution Ultrasound in the Preoperative Assessment of Margins of Basal Cell and Squamous Cell Carcinoma in Patients Undergoing Mohs Micrographic Surgery

    BACKGROUND Noninvasive techniques to assess subclinical spread of nonmelanoma skin cancer (NMSC) may improve surgical precision. High-resolution ultrasound has shown promise in evaluating the extent of NMSC. OBJECTIVES To determine the accuracy of high-resolution ultrasound to assess the margins of basal cell (BCC) and squamous cell carcinomas (SCC) before Mohs micrographic surgery (MMS). METHODS We enrolled 100 patients with invasive SCC or BCC. Before the first stage of MMS, a Mohs surgeon delineated the intended surgical margin. Subsequently, a trained ultrasound technologist independently evaluated disease extent using the EPISCAN I-200 to evaluate tumor extent beyond this margin. The accuracy of high-resolution ultrasound was subsequently tested by comparison with pathology from frozen sections. RESULTS The test characteristics of the high-resolution ultrasound were sensitivity=32%, specificity=88%, positive predictive value=47%, and negative predictive value=79%. Subgroup analyses demonstrated better test characteristics for tumors larger than the median (area>1.74 cm2). Qualitative analyses showed that high-resolution ultrasound was less likely to identify extension from tumors with subtle areas of extension, such as small foci of dermal invasion from infiltrative SCC and micronodular BCC. CONCLUSION High-resolution ultrasound requires additional refinements to improve the preoperative determination of tumor extent before surgical treatment of NMSC. [source]

    Presurgical Curettage Appropriately Reduces the Number of Mohs Stages by Better Delineating the Subclinical Extensions of Tumor Margins

    Vinh Q. Chung MD
    Background. Whether presurgical curettage (PC), light curettage performed before Mohs surgery to delineate tumor margin, is appropriate or causes unnecessary removal of normal tissue has not been well established. Objective. We aim to determine histologically whether PC appropriately increases the size of the stage I specimen or causes unnecessary removal of healthy tissue. Methods. Before a surgical margin guided by PC was taken, a hypothetical margin determined by visual and tactile assessment alone (no curettage [NC]) was marked outside the clinically defined tumor. Histologic analysis at the NC and the PC margins revealed whether the increase in the stage I specimen as a result of PC was appropriate. Results. PC appropriately increased the stage I specimen in 21 cases and unnecessarily removed normal tissue in only 1 case. The estimation of tumor margins with PC was 15 times more accurate than with NC (p value = .0012). Conclusion. For basal cell and squamous cell carcinomas at least 4 mm in diameter, light curettage performed prior to Mohs surgery could better delineate subclinical extensions of the tumor margin and appropriately increase the size of the stage I specimen. [source]

    The Efficacy of Curettage in Delineating Margins of Basal Cell Carcinoma Before Mohs Micrographic Surgery

    Désirée Ratner MD
    Background. Curettage may be helpful as a preliminary step to outline the gross subclinical extensions of high-risk basal cell carcinomas (BCCs) before the first stage of Mohs micrographic surgery. Although many Mohs surgeons use curettage in the Mohs surgical setting, no prospective studies have as yet been performed that demonstrate the efficacy of curettage in delineating tumor margins before Mohs surgery. Objective. To document the efficacy of curettage in delineating BCC margins before Mohs micrographic surgery. Methods. This was a prospective evaluation of 599 patients with biopsy-proven BCCs treated with Mohs surgery. The preoperative dimensions of each tumor, the curetted dimensions before the first surgical stage, the proposed excisional margins before each surgical stage, and the final defect dimensions after each surgical stage were measured. The maximum curetted margin around each tumor was calculated and compared with typical Mohs excisional margins of 1, 2, 3, and 4 mm. A hypothetical 1-, 2-, 3-, or 4-mm excisional margin was added to the preoperative X and Y dimensions of each tumor, and the actual final defect sizes were compared with the hypothetical final defect sizes to determine whether an additional surgical stage would have been needed had curettage not been performed. The amount of tissue stretch occurring after specimen removal was calculated to determine whether tissue stretch falsely elevated the number of instances in which an additional surgical stage would have been needed had curettage not been performed. Results. The curetted margin around the observed extent of each tumor exceeded 1 mm in 87.6% of cases, 2 mm in 47.1% of cases, 3 mm in 19.7% of cases, and 4 mm in 5.7% of cases. The mean curetted margin was 1.7 mm. Taking a 1-mm margin in the first stage of Mohs surgery without first performing curettage would have necessitated an extra surgical stage in 99.2% of cases, whereas taking a 2-, 3-, or 4-mm margin would have necessitated an extra surgical stage in 93.0%, 88.1%, and 49.4% of cases, respectively. After calculating and eliminating the effects of tissue stretch, it was found that a 1-mm excisional margin taken in the first stage of Mohs surgery without first performing curettage would have necessitated an extra surgical stage in 99.0% of the cases. Taking a 2-, 3-, or 4-mm margin would have necessitated an extra surgical stage in 87.5%, 57.9%, and 29.5% of cases, respectively. Conclusion. Careful debulking and palpation with the curette significantly reduce the number of Mohs surgical stages required for BCC clearance. Even after taking the effects of tissue stretch into consideration, a significant proportion of tumors would still require an additional stage for tumor clearance without aggressive presurgical curettage. [source]

    Falling Apart at the Margins?

    Neighbourhood Transformations in Peri-Urban Chennai
    ABSTRACT This article explores the peri-urban dynamics in developing cities using a theoretical examination of the metropolis as the new urban condition. Although a western conceptualization, the notion of the metropolis, and particularly metropolitan planning, was exported to the developing world to address its urbanization problems. Metropolitan development authorities were established for wider city regions and accorded legislative powers to prepare master plans for the metropolitan areas. However, in most instances, their planning strategies resulted in a conflation of the urban,rural interface into a more complex peri-urban condition, marked by heterogeneity and fragmentation. The article illustrates this through an empirical investigation in the Indian city of Chennai, where socio-spatial transformations of two borderland neighbourhoods on its southern periphery are assessed mainly in terms of metropolitan planning decisions over the decades. In outlining their metamorphosis, the study is careful not to perceive such conflicts as simple forms of polarization between the rich and the poor. Rather, it sets the class conflicts against the politico-economic dynamics yielding newer forms of polarization in the peri-urban spaces. [source]