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Crater
Kinds of Crater Terms modified by Crater Selected AbstractsA simulation of the hydrothermal response to the Chesapeake Bay bolide impactGEOFLUIDS (ELECTRONIC), Issue 3 2005W. E. SANFORD Abstract Groundwater more saline than seawater has been discovered in the tsunami breccia of the Chesapeake Bay Impact Crater. One hypothesis for the origin of this brine is that it may be a liquid residual following steam separation in a hydrothermal system that evolved following the impact. Initial scoping calculations have demonstrated that it is feasible such a residual brine could have remained in the crater for the 35 million years since impact. Numerical simulations have been conducted using the code HYDROTHERM to test whether or not conditions were suitable in the millennia following the impact for the development of a steam phase in the hydrothermal system. Hydraulic and thermal parameters were estimated for the bedrock underlying the crater and the tsunami breccia that fills the crater. Simulations at three different breccia permeabilities suggest that the type of hydrothermal system that might have developed would have been very sensitive to the permeability. A relatively low breccia permeability (1 × 10,16 m2) results in a system partitioned into a shallow water phase and a deeper superheated steam phase. A moderate breccia permeability (1 × 10,15 m2) results in a system with regionally extensive multiphase conditions. A relatively high breccia permeability (1 × 10,14 m2) results in a system dominated by warm-water convection cells. The permeability of the crater breccia could have had any of these values at given depths and times during the hydrothermal system evolution as the sediments compacted. The simulations were not able to take into account transient permeability conditions, or equations of state that account for the salt content of seawater. Results suggest, however, that it is likely that steam conditions existed at some time in the system following impact, providing additional evidence that is consistent with a hydrothermal origin for the crater brine. [source] The geochemical characterization and correlation of Late Holocene tephra layers at Ambra Crater and Kuk Swamp, Papua New GuineaGEOLOGICAL JOURNAL, Issue 5 2009Sarah E. Coulter Abstract Major element geochemical analyses of volcanic glass shards from visible, macroscopic tephra layers in Papua New Guinea were used to test field-based correlations between local Late Holocene sequences. Previously, synchronization of sediment records at archaeological and palaeoecological sites across the Papua New Guinea highlands had been based largely on the physical properties and stratigraphic relationships of visible volcanic layers. The geochemical analysis of tephra-derived glass demonstrates miscorrelations and enables more robust tephrostratigraphic links to be made between a globally significant archaeological site, Kuk Swamp, and a nearby volcanic cone, Ambra Crater. The results indicate that field-based correlations of tephras can be problematic, especially given variable post-depositional changes in colour and texture of relatively thin tephra layers in different depositional environments. Additionally, the findings call into question some previous tephrochronological associations at archaeological and palaeoecological sites in the Papua New Guinea highlands, and demonstrate the necessity of grain-discrete geochemical analysis of glass shards as a basis for future tephrochronological studies in this region. Copyright © 2009 John Wiley & Sons, Ltd. [source] Targeted driving using visual tracking on Mars: From research to flightJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 3 2009Won S. Kim This paper presents the development, validation, and deployment of the visual target tracking capability onto the Mars Exploration Rover (MER) mission. Visual target tracking enables targeted driving, in which the rover approaches a designated target in a closed visual feedback loop, increasing the target position accuracy by an order of magnitude and resulting in fewer ground-in-the-loop cycles. As a result of an extensive validation, we developed a reliable normalized cross-correlation visual tracker. To enable tracking with the limited computational resources of a planetary rover, the tracker uses the vehicle motion estimation to scale and roll the template image, compensating for large image changes between rover steps. The validation showed that a designated target can be reliably tracked within several pixels or a few centimeters of accuracy over a 10-m traverse using a rover step size of 10% of the target distance in any direction. It also showed that the target is not required to have conspicuous features and can be selected anywhere on natural rock surfaces excluding rock boundary and shadowed regions. The tracker was successfully executed on the Opportunity rover near Victoria Crater on four distinct runs, including a single-sol instrument placement. We present the flight experiment data of the tracking performance and execution time. © 2009 Wiley Periodicals, Inc. [source] Redating the onset of burning at Lynch's Crater (North Queensland): implications for human settlement in AustraliaJOURNAL OF QUATERNARY SCIENCE, Issue 8 2001C. S. M. Turney Abstract Lynch's Crater preserves a continuous, high-resolution record of environmental changes in north Queensland. This record suggests a marked increase in burning that appears to be independent of any known major climatic boundaries. This increase is accompanied, or closely followed, by the virtually complete replacement of rainforest by sclerophyll vegetation. The absence of any major climatic shift associated with this increase in fire frequency therefore has been interpreted as a result of early human impact in the area. The age for this increase in burning, on the basis of conventional radiocarbon dating, was previously thought to be approximately 38 000 14C yr BP, supporting the traditional model for human arrival in Australia at 40 000 14C yr BP Here we have applied a more rigorous pre-treatment and graphitisation procedure for radiocarbon dating samples from the Lynch's Crater sequence. These new dates suggest that the increase in fire frequency occurred at 45 000 14C yr BP, supporting the alternative view that human occupation of Australia occurred by at least 45 000,55 000 cal. yr BP. Copyright © 2001 John Wiley & Sons, Ltd. [source] Reduced dispersal and opportunistic territory acquisition in male lions (Panthera leo)JOURNAL OF ZOOLOGY, Issue 2 2003Paul J. Funston Abstract Life-history patterns in lions Panthera leo living in savanna woodlands of the Kruger National Park, South Africa, were investigated and compared with those of the Tanzanian ,plains-like' ecosystems (e.g. Serengeti Plains and Ngorongoro Crater). First, lower levels of mortality in the juvenile age classes were found in Kruger lions, which in turn, extend the inter-birth period. A further difference was a prolonged period of association of sub-adult males with their natal pride, either directly or in a land tenure system that has not been described previously. Most (80%) of young male coalitions rather than becoming nomadic, remained close to their natal territory after leaving the pride, either as non-territorial sub-adults or adults and even as territorial adults. Only 20% of coalitions did not stay close to their natal range, one of which acquired a territory 20 km away from its natal pride. The pattern of territory acquisition, in fact, was one in which the majority of holders acquired territories close to their natal ranges. These behaviour patterns contrast markedly with those from ,plains-like' ecosystems where dispersing males usually move far away from their natal pride's range (>200) km and often remain nomadic for extended periods of time. Dense bush and access to sufficient prey resources in the form of resident buffalo Syncerus caffer herds may be important factors allowing extended residence near the natal pride's territory. Buffalo were more available in our study area habitat than in neighbouring habitats, and comprised the majority of male lion kills. Extended male residence contrasts markedly with current theory on dispersal in polygynous mammals, which holds that only one sex (females for lions) gain an advantage by staying close to the territory of their natal pride. In Kruger it seems that both sexes gain an advantage by not dispersing far, and use currently undocumented mechanisms to avoid inbreeding. [source] The Canyon Diablo impact event: Projectile motion through the atmosphereMETEORITICS & PLANETARY SCIENCE, Issue 1 2009Natalia ARTEMIEVA Its location in arid northern Arizona has been ideal for the preservation of the structure and the surviving meteoric material. The recovery of a large amount of meteoritic material in and around the crater has allowed a rough reconstruction of the impact event: an iron object 50 m in diameter impacted the Earth's surface after breaking up in the atmosphere. The details of the disruption, however, are still debated. The final crater morphology (deep, bowl-shaped crater) rules out the formation of the crater by an open or dispersed swarm of fragments, in which the ratio of swarm radius to initial projectile radius Cd is larger than 3 (the final crater results from the sum of the craters formed by individual fragments). On the other hand, the lack of significant impact melt in the crater has been used to suggest that the impactor was slowed down to 12 km/s by the atmosphere, implying significant fragmentation and fragments' separation up to 4 initial radii. This paper focuses on the problem of entry and motion through the atmosphere for a possible Canyon Diablo impactor as a first but necessary step for constraining the initial conditions of the impact event which created Meteor Crater. After evaluating typical models used to investigate meteoroid disruption, such as the pancake and separated fragment models, we have carried out a series of hydrodynamic simulations using the 3D code SOVA to model the impactor flight through the atmosphere, both as a continuum object and a disrupted swarm. Our results indicate that the most probable pre-atmospheric mass of the Meteor Crater projectile was in the range of 4.108to 1.2.109kg (equivalent to a sphere 46,66 m in diameter). During the entry process the projectile lost probably 30% to 70% of its mass, mainly because of mechanical ablation and gross fragmentation. Even in the case of a tight swarm of particles (Cd < 3), small fragments can separate from the crater-forming swarm and land on the plains (tens of km away from the crater) as individual meteorites. Starting from an impactor pre-atmospheric velocity of ,18 km/s, which represents an average value for Earth-crossing asteroids, we find that after disruption, the most probable impact velocity at the Earth's surface for a tight swarm is around 15 km/s or higher. A highly dispersed swarm would result in a much stronger deceleration of the fragments but would produce a final crater much shallower than observed at Meteor Crater. [source] Identification of shocked quartz by scanning cathodoluminescence imagingMETEORITICS & PLANETARY SCIENCE, Issue 6 2001Sam Boggs Jr. These lamellae appear as remarkably straight, thin, planar features (microstructures) in sets within which lamellae are essentially parallel to each other and spaced , 20 ,m apart. Two or more intersecting sets are typically present. Shock lamellae are commonly recognized and identified by optical methods, by use of the transmission electron microscope (TEM), and by etching polished sections and subsequent examination with a scanning electron microscope (SEM) operated in the secondary electron mode. We present here a method for observing planar microstructures in shocked quartz by using a cathodoluminescence (CL) detector attached to a SEM. The method relies on the fact that planar microstructures in quartz arising as a result of shock display no CL whatever; thus, they show up as distinct, thin, black lines on otherwise luminescent quartz grains. We used scanning CL imaging to study shocked quartz from the Ries Crater, Germany, a well-known impact crater of Miocene age. We demonstrate that shock-produced planar microstructures are clearly displayed in SEM-CL images and can be distinguished from microfractures generated by tectonism, and subsequently filled with quartz, and other similar features not related to impact events. The SEM-CL method provides a powerful supplement to other methods of identifying shocked quartz. It commonly provides better spatial resolution than does standard optical methods, and does not require etching of quartz grains. Further, it is easier and faster to use than are TEM methods, although it is not capable of the fine-scale defect analysis possible with TEM. [source] Books and Multimedia ReviewsMETEORITICS & PLANETARY SCIENCE, Issue 12 2002Article first published online: 26 JAN 2010 Book reviewed in this article: Chemical Dynamics in Extreme Environments, Volume 11 of Advanced Series in Physical Chemistry edited by Rainer A. Dressler. Storms in Space by John Freeman. Major Impacts and Plate Tectonics: A Model for the Phanerozoic Evolution of the Earth's Lithosphere by Neville J. Price. Meteorite Hunter: The Search For Siberian Meteorite Craters by Roy A. Gallant. [source] Effect of Hypervelocity Impact on Microcellular Ceramic Foams from a Preceramic PolymerADVANCED ENGINEERING MATERIALS, Issue 11 2003P. Colombo A promising material for hypervelocity impact shields in spacecraft and satellites has been found in lightweight microcellular SiOC foams. The foam stops the projectile and the debris from the impacted bumper facesheet within a few millimeters (see Figure for a cross-section of the crater) at speeds up to 5.1 km,s,1. The impacted SiOC ceramic did not react with incoming debris, and no phase transformation or compositional change was observed. [source] Water pipeline failure due to water hammer effectsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 12 2006C. SCHMITT ABSTRACT A numerical model has been established in order to simulate the propagation of pressure waves in water networks. The present model formulation is based on a system of partial hyperbolic differential equations. This system has been solved via the characteristics method. The current model provides the necessary data and the necessary damping of water hammer waves, taking into account the structure of the pipe network and the pressure loss. The numerical algorithm estimates the maximum pressure values resulting from the water hammer when closing valves in the network and consequently, the maximum stresses in the pipes have been calculated. In the case of simultaneous closing of several valves, the over pressure can exceed the admissible pressure. In this case, the severity of a defect such as a corrosion crater (pit) has been estimated by computing a safety factor for the stress distribution at the defect tip. This allows the applied notch stress intensity factor to be obtained. To investigate the defect geometry effects, semi-spherical and semi-elliptical defects are deemed to exist in up to one-half of the thickness of the pipe wall. The outcomes have been introduced into the structural integrity assessment procedure (SINTAP) failure diagram assessment (FAD) in order to obtain the safety factor value. Conventionally, it is considered that a failure hazard exists if this safety factor is less than two. [source] Principal features of impact-generated hydrothermal circulation systems: mineralogical and geochemical evidenceGEOFLUIDS (ELECTRONIC), Issue 3 2005MIKHAIL V. NAUMOVArticle first published online: 14 JUL 200 Abstract Any hypervelocity impact generates a hydrothermal circulation system in resulting craters. Common characteristics of hydrothermal fluids mobilized within impact structures are considered, based on mineralogical and geochemical investigations, to date. There is similarity between the hydrothermal mineral associations in the majority of terrestrial craters; an assemblage of clay minerals,zeolites,calcite,pyrite is predominant. Combining mineralogical, geochemical, fluid inclusion, and stable isotope data, the distinctive characteristics of impact-generated hydrothermal fluids can be distinguished as follows: (i) superficial, meteoric and ground water and, possibly, products of dehydration and degassing of minerals under shock are the sources of hot water solutions; (ii) shocked target rocks are sources of the mineral components of the solutions; (iii) flow of fluids occurs mainly in the liquid state; (iv) high rates of flow are likely (10,4 to 10,3 m s,1); (v) fluids are predominantly aqueous and of low salinity; (vi) fluids are weakly alkaline to near-neutral (pH 6,8) and are supersaturated in silica during the entire hydrothermal process because of the strong predominance of shock-disordered aluminosilicates and fusion glasses in the host rocks; and (vii) variations in the properties of the circulating solutions, as well as the spatial distribution of secondary mineral assemblages are controlled by tempera ure gradients within the circulation cell and by a progressive cooling of the impact crater. Products of impact-generated hydrothermal processes are similar to the hydrothermal mineralization in volcanic areas, as well as in modern geothermal systems, but impacts are always characterized by a retrograde sequence of alteration minerals. [source] A simulation of the hydrothermal response to the Chesapeake Bay bolide impactGEOFLUIDS (ELECTRONIC), Issue 3 2005W. E. SANFORD Abstract Groundwater more saline than seawater has been discovered in the tsunami breccia of the Chesapeake Bay Impact Crater. One hypothesis for the origin of this brine is that it may be a liquid residual following steam separation in a hydrothermal system that evolved following the impact. Initial scoping calculations have demonstrated that it is feasible such a residual brine could have remained in the crater for the 35 million years since impact. Numerical simulations have been conducted using the code HYDROTHERM to test whether or not conditions were suitable in the millennia following the impact for the development of a steam phase in the hydrothermal system. Hydraulic and thermal parameters were estimated for the bedrock underlying the crater and the tsunami breccia that fills the crater. Simulations at three different breccia permeabilities suggest that the type of hydrothermal system that might have developed would have been very sensitive to the permeability. A relatively low breccia permeability (1 × 10,16 m2) results in a system partitioned into a shallow water phase and a deeper superheated steam phase. A moderate breccia permeability (1 × 10,15 m2) results in a system with regionally extensive multiphase conditions. A relatively high breccia permeability (1 × 10,14 m2) results in a system dominated by warm-water convection cells. The permeability of the crater breccia could have had any of these values at given depths and times during the hydrothermal system evolution as the sediments compacted. The simulations were not able to take into account transient permeability conditions, or equations of state that account for the salt content of seawater. Results suggest, however, that it is likely that steam conditions existed at some time in the system following impact, providing additional evidence that is consistent with a hydrothermal origin for the crater brine. [source] WATER RESOURCES OF THE CHUNCHUCMIL MAYA,GEOGRAPHICAL REVIEW, Issue 4 2000Sheryl Luzzadder-Beach ABSTRACT. Chunchucmil, on the Yucatán Peninsula, was densely populated in the Maya Late Classic period (ca. a.d. 550,830), even though it depends principally on groundwater. In the 1990s, hydrologic investigations were conducted to determine whether groundwater could have met domestic and agricultural needs. The region's groundwater is near the surface and is influenced by sea-level fluctuations; however, geochemical analysis revealed that groundwater quality is not affected by mixing with seawater. The potential exists for high and spatially extensive nitrate contamination in this karstic area, yet water-quality analyses revealed only moderate levels of nitrate in the groundwater. Agricultural limitations are imposed by chloride, total dissolved solids, and salinity, as indicated by electrical conductivity; domestic water use is limited by the presence of nitrate, sulfate, and chloride. Throughflow in the ring of cenotes (sinkholes) around the Chicxulub impact crater may explain the movement and spatial distribution of water-quality constituents in Chunchucmil's groundwater. [source] Swarms of microearthquakes associated with the 2005 Vulcanian explosion sequence at Volcán de Colima, MéxicoGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2010Vyacheslav M. Zobin SUMMARY The swarms of microearthquakes, that appeared at Volcán de Colima, México before and after its large 2005 Vulcanian explosions, are discussed. The study of 966 microearthquakes is based on the seismic records of short-period seismic station EZV4 situated at a distance of 1.7 km from the crater. Three samples of microearthquakes were selected: the seismic records associated with a single 2005 September 16 large explosion, and the seismic records associated with two sequences of large explosions, the 2005 March 10 and 13 explosions and the 2005 May 30 and June 2, 5 and 7 explosions. These explosions were seven of 15 large explosions (E, 1011 J) that occurred during the 2005 explosive sequence. The microearthquake waveforms were identified as the records of rockfalls and microexplosions. The explosive microearthquakes represent from 84 to 89 per cent of the total number of microearthquakes with the readable waveforms. The dominant frequencies of the explosive microearthquakes were 2.8 Hz for the 2005 March explosion sequence and 2005 September 16 explosion, and 1.3, 2.0 and 2.8 Hz for the 2005 May-June explosion sequence. Energy of microexplosions that generated the microearthquake waveforms ranged from 104 to 7 × 107 J. The force component, corresponding to the largest microexplosive events, was estimated at a level from 3.1 × 107 to 3.6 × 108 N. The appearance of microearthquakes before large volcanic explosions and the sharp increase in their rate of appearance some hours before an explosion makes them a useful instrument for volcano monitoring. [source] Numerical simulation of the fracture process in cutting heterogeneous brittle materialINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 13 2002H. Y. Liu Abstract The process of cutting homogeneous soft material has been investigated extensively. However, there are not so many studies on cutting heterogeneous brittle material. In this paper, R-T2D (Rock and Tool interaction), based on the rock failure process analysis model, is developed to simulate the fracture process in cutting heterogeneous brittle material. The simulated results reproduce the process involved in the fragmentation of rock or rock-like material under mechanical tools: the build-up of the stress field, the formation of the crushed zone, surface chipping, and the formation of the crater and subsurface cracks. Due to the inclusion of heterogeneity in the model, some new features in cutting brittle material are revealed. Firstly, macroscopic cracks sprout at the two edges of the cutter in a tensile mode. Then with the tensile cracks releasing the confining pressure, the rock in the initially high confining pressure zone is compressed into failure and the crushed zone gradually comes into being. The cracked zone near the crushed zone is always available, which makes the boundary of the crushed zone vague. Some cracks propagate to form chipping cracks and some dip into the rock to form subsurface cracks. The chipping cracks are mainly driven to propagate in a tensile mode or a mixed tensile and shear mode, following curvilinear paths, and finally intersect with the free surface to form chips. According to the simulated results, some qualitative and quantitative analyses are performed. It is found that the back rake angle of the cutter has an important effect on the cutting efficiency. Although the quantitative analysis needs more research work, it is not difficult to see the promise that the numerical method holds. It can be utilized to improve our understanding of tool,rock interaction and rock failure mechanisms under the action of mechanical tools, which, in turn, will be useful in assisting the design of fragmentation equipment and fragmentation operations. Copyright © 2002 John Wiley & Sons, Ltd. [source] Multiple keratoacanthomas in a young woman: report of a case emphasizing medical management and a review of the spectrum of multiple keratoacanthomasINTERNATIONAL JOURNAL OF DERMATOLOGY, Issue 1 2007Ron J. Feldman MD A 27-year-old white woman was referred for consultation with regard to the presence of extensive multiple keratotic lesions. She began to develop these lesions at the age of 9 years, with healing of the lesions resulting in scar formation. A biopsy was performed at the age of 16 years, but the patient was unsure of the results. Since then, she had not had any treatment or biopsies, and stated that she had not suffered from any health problems during the intervening period. She was most concerned about the tumors on her heels and soles, which caused difficulty with ambulation. The family history was negative for skin diseases, including melanoma, nonmelanoma skin cancer, psoriasis, and eczema, and positive for Type II diabetes mellitus. A relative reported that the patient's grandfather had similar lesions, but the patient's parents and siblings were healthy. She was married and had one child, a 9-year-old daughter. Her child had no skin lesions. The patient's only medication was Ortho-Tricyclene birth control pills. She had no known drug allergies. Physical examination revealed the presence of multiple lesions on her body (Fig. 1). Her left superior helix contained a well-demarcated, dome-shaped nodule with a rolled, mildly erythematous border with a central hyperkeratotic plug. A similar lesion was present in the scaphoid fossa of the left ear and smaller lesions were scattered on her face. Numerous lesions were present on the arms and legs bilaterally, with the majority of lesions being located on the anterior lower legs. There were also lesions present on the palms and soles. The lesions ranged in size from 5 mm to 3 cm, the largest being a verrucous exophytic nodule on the anterior aspect of her left leg. Overall, there appeared to be two distinct types of lesion. One type appeared round, oval, and symmetric with a central keratotic plug, similar to that on the ear. The other type was larger, more exophytic, and verrucous, including the lesions on the volar surfaces. Also present were numerous, irregularly shaped atrophic scars where previous lesions had healed spontaneously. There were no oral lesions or lesions on her fingernails or toenails, and her teeth and hair were normal. Figure 1. Initial presentation of left ear and anterior legs before treatment A biopsy was obtained from an early lesion on the right dorsal forearm. Histology revealed an exo-/endophytic growth having a central crater containing keratinous material (Fig. 2). The crater was surrounded by markedly hyperplastic squamous epithelium with large squamous epithelial cells having abundant glassy cytoplasm. Some cells were dyskeratotic. Within the dermis was a dense, chiefly mononuclear inflammatory infiltrate. A buttress of epidermis surrounded the crater. The clinical and pathologic data were consistent with keratoacanthomas. Figure 2. Keratoacanthoma exhibiting an exo- and endophytic growth pattern with a central crater containing keratin (hematoxylin and eosin; original magnification, ×40) Initial laboratory screenings revealed elevated triglycerides and total cholesterol, 537 mg/dL (normal, < 150 mg/dL) and 225 mg/dL (normal, < 200 mg/dL), respectively, with all other laboratory results within normal limits. In anticipation of starting oral retinoid therapy for her multiple keratoacanthomas, she was referred to her primary care physician for control of hyperlipidemia. After her lipids had been controlled, she was placed on isotretinoin (Accutane) 40 mg/day. There was some interval improvement with regression of some lesions leaving atrophic scars. She was also started on topical application of tazarotene (Tazorac) for all nonresolving lesions. Possible side-effects from the isotretinoin occurred, including dry mouth and eyes. After 8 months of isotretinoin, the patient was switched to acitretin (Soriatane) 25 mg to determine whether it might have a more beneficial effect on the resistant lesions. Many of the larger lesions regressed leaving atrophic scars. The dose of acitretin was subsequently increased to 35 mg because the lesions on her heel and the ball of her foot persisted. Almost all of the lesions resolved, except those on her feet, which are slowly regressing. Currently, the patient is on a regimen of acitretin 25 mg once a day with tazarotene 0.1% gel applied directly to the few residual keratoacanthomas on her feet, which are slowly improving. [source] Two cases of reactive perforating collagenosis arising at the site of healed herpes zosterINTERNATIONAL JOURNAL OF DERMATOLOGY, Issue 3 2001Hye Nam Lee MD Case 1 A 67-year-old South Korean woman presented with a painful eruption on the left trunk. Several groups of vesicles with an erythematous and edematous base were situated unilaterally within the distribution of the left T9 dermatome; they had been present for 7 days. A diagnosis of herpes zoster was made, and treatment with acyclovir, analgesics, tranquilizers, and wet dressings produced a moderate response. Two weeks after onset, the lesions appeared to have healed with a scar. Four months later, however, the patient noticed another eruption of papules in the postherpetic area (Fig. 1A,B). Figure 1. Case 1. (A) Multiple erythematous papules on the left trunk along the T9 dermatome. (B) Multiple erythematous papules with a keratotic central plug The biopsy specimen showed a cup-shaped epidermal invagination filled with a keratotic plug containing basophilic debris and collagen, with perforation of the epidermis. Masson's trichrome stain identified refractile fibers within the epidermis as hyalinized and degenerating collagen. Van Gieson staining for elastic fibers was negative in the epidermis and in the crater. These findings are consistent with reactive perforating collagenosis (RPC). Case 2 A 66-year-old South Korean woman developed herpes zoster of the left neck and shoulder, which resolved after an uncomplicated course. Two months later, a zosteriform, pink, papular eruption developed at the site of the resolved herpes zoster. Examination revealed multiple, erythematous papules with a central umbilication containing a firmly adherent keratotic plug on the left shoulder and neck (Fig. 2A). Figure 2. Case 2. (A) Multiple erythematous papules on the left neck and shoulder along the C4 dermatome. (B) Cup-shaped epidermal invagination filled with keratotic plug containing basophilic debris and degenerated collagen, with perforation of the epidermis (hematoxylin and eosin stain, ×,100) The biopsy specimen showed a dome-shaped lesion with a central crater that extended from the epidermis to the papillary dermis and contained degenerated collagen in vertical strands (Fig. 2B). [source] Provenance Determination of Oriental Porcelain Using Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS),JOURNAL OF FORENSIC SCIENCES, Issue 2 2007Emma K. Bartle B.Sc. ABSTRACT: The sale of fraudulent oriental ceramics constitutes a large proportion of the illegal artifact and antique trade and threatens to undermine the legitimate international market. The sophistication and skill of forgers has reached a level where, using traditional appraisal by eye and hand, even the most experienced specialist is often unable to distinguish between a genuine and fraudulent piece. In addition, current provenancing techniques such as energy-dispersive X-ray fluorescence (EDXRF) spectrometry and thermoluminescence (TL) dating can result in significant damage to the artifact itself. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), a relatively nondestructive analytical technique, has been used for the provenance determination of materials based on geographical origin. The technique requires the production of a laser crater, c. 100 ,m in diameter, which is essentially invisible to the naked eye. Debris from this crater is analyzed using ICP-MS, with the results forming the basis of the provenance establishment protocol. Chinese, Japanese, and English porcelain shards have been analyzed using this protocol and generic isotopic distribution patterns have been produced that enable the provenance establishment of porcelain artifacts to their country of production. Minor variations between elemental fingerprints of artifacts produced in the same country also indicate that it may be possible to further provenance oriental ceramics to a specific production region or kiln site. [source] The Dynamic Interaction of Water with Four Dental Impression Materials During CureJOURNAL OF PROSTHODONTICS, Issue 4 2009Dariush Hosseinpour PhD Abstract Purpose: The purpose of this work was to investigate the interaction of water with four different dental impression materials: Aquasil (Ultra XLV Type 3), Take 1 (Wash Regular Set), Genie (Light Body, Standard Set), and Impregum Garant (Soft Light Bodied Consistency). Materials and Methods: Apparent contact angles of de-ionized water made against thin horizontal sample films of the different materials under different conditions were measured from analysis of profile images of symmetrical sessile drops of water placed on the sample films using a Model FTÅ200 dynamic drop shape analysis system, which included a JAI M30 high speed CCD camera combined with a zoom microscope. Data were taken for specimens of dry ages (times following mixing) from a minimum of 20 seconds up to 1220 seconds. Imaging was started before the initial water/impression material contact, and lasted for at least 420 seconds in each case. The interval at the beginning of each run was 0.033 second, and then increased by a factor of 1.012 to the end. During the initial 3 seconds following the drop deposition, the drop's shape oscillated due to inertial effects, so apparent contact angle data during this period were neglected in all cases. All measurements were made at room temperature. The drops were enclosed in a humidified chamber that suppressed evaporation. All data were repeated at least five times, and results were analyzed where appropriate using one-way ANOVA. Microscopic images of the water/impression material interactions for fresh (uncured) materials were acquired to reveal the destructive interactions that resulted from such contact. Finally, surface tension measurements were made of water that had been contacted with material of varying dry age using the pendant drop method capability of the drop shape analysis system. These helped to assess the origin of hydrophilicity development for the different materials. Results: For short curing times (dry ages), water showed a destructive effect on the integrity of all of the impression materials, as evidenced by the formation of a crater beneath the water drop and a scum of material at its surface. These effects diminished with dry age until a critical curing time was reached, beyond which such destructive interactions were no longer detectable. These critical curing times were determined to be 80, 140, 110, and 185 seconds for Aquasil, Take 1, Genie, and Impregum, respectively. The initial contact angle following the respective critical curing time was lowest for Impregum, at 66°; while values for Aquasil, Genie, and Take 1 were 93°, 104°, and 110°, respectively. Beyond the critical curing times for the different materials, different degrees of hydrophilicity were observed. Aquasil showed the lowest final contact angle (<10°), with Impregum, Take 1, and Genie showing 31°, 34°, and 40°, respectively. Measurements of the surface tension of water after contact with the different materials suggested that for Aquasil, hydrophilicity appears to be developed through the leaching of surfactant from the material, whereas for Impregum, Take 1, and Genie, hydrophilicity is developed at least in part through a change in surface structure in contact with water. Impregum and Aquasil materials of dry ages well beyond the critical curing time exhibited a stick-slip behavior in their interline movement or contact angle evolution. This was believed to be due to the slowness in the leaching of surfactant (in the case of Aquasil) or the re-orientation of unleachable surface groups (in the case of the other materials) in comparison to the inherent kinetics of water drop spreading. Conclusions: All materials investigated in the fresh, uncured state showed qualitative decomposition when put in contact with water through the formation of a crater beneath the water drop and a scum of material at its surface. These effects diminished with curing time until beyond a critical value, no such effects were evident. The initial hydrophilicity of the materials as determined by the contact angles obtained at their respective critical dry ages was greatest for Impregum. Beyond the critical curing time, different degrees of hydrophilicity were observed, with Aquasil showing the lowest final contact angle. [source] An example of the complementarity of laser-induced breakdown spectroscopy and Raman microscopy for wall painting pigments analysisJOURNAL OF RAMAN SPECTROSCOPY, Issue 7 2007Romain Bruder Abstract Laser-induced breakdown spectroscopy (LIBS) and Raman microscopy were used for the identification of pigments in wall painting. Raman spectroscopy, which provides the molecular ,fingerprint' of the compound, is nowadays widely used by the archaeometry community, especially for pigment analysis. LIBS, which provides the elementary composition of samples, is a rapid noncontact method, enabling layer-by-layer analysis through a precise laser ablation of the sample. This work deals with the behavior of pigments after a LIBS analysis, by trying to identify the compounds before and after the laser shot. Six commercial pigments prepared with the fresco technique were investigated: ultramarine blue, red lead, charcoal, a yellow and a red ochre, and a green earth. Raman spectra, acquired on the sample surface and in the crater induced by LIBS analysis, were compared. The results show that these pigments are well recognized after a LIBS measurement. The analysis of green earth illustrates that the combination of these two techniques gives complete information from a sample. Copyright © 2007 John Wiley & Sons, Ltd. [source] Environmental niche of the smut lizard population on a sandy coastal ecosystem of Southeastern Tenerife (Canary Islands)MARINE ECOLOGY, Issue 2008Antonio De Los Santos Abstract Relationships among environmental patterns and population size of the smut lizard Gallotia galloti galloti Oudart, 1839 (Sauria Lacertidae) were examined in the context of longer time-scale variability on a sandy beach and adjacent environments of Southeastern Tenerife. Seasonal and yearly patterns in the population size were likewise analyzed in relation to climatic and anthropic variables. Six sampling plots (coastal, sweet tabaiba, tuff, lava, sandy lava and crater) were selected following a perpendicular transect to the sandy fringe that extends from the beach toward the volcanic interior. Pitfall trapping was conducted from 1984 to 2005, and capture,mark,recapture technique and the Jolly,Seber method were used to estimate population sizes. The highest population size estimates were shown on the sandy lava plot and the neighboring lava plot, reaching values of about 3500 individuals ha,1 during the spring. The population was active almost the whole year, with seasonal patterns of activity from March to October. Seasonal temperature and population size patterns were correlated but the ,calima' episodes produced some disturbance. Gallotia galloti galloti was one of the most abundant lizards of all the species studied and its population size has not remained stable over the study period, probably because of the absence of predation and competition, and because of human interference and environmental instability. [source] Geophysical survey of the proposed Tsenkher impact structure, Gobi Altai, MongoliaMETEORITICS & PLANETARY SCIENCE, Issue 3 2010Jens ORMÖ Extensive occurrences of brecciated rocks, mainly in the form of an ejecta blanket outside the elevated rim of the structure, support an explosive origin (e.g., cosmic impact, explosive volcanism). The host rocks in the area are mainly weakly magnetic, silica-rich sandstones, and siltstones. A near absence of surface exposures of volcanic rocks makes any major volcanic structures (e.g., caldera) unlikely. Likewise, the magnetic models exclude any large, subsurface, intrusive body. This is supported by an 8 mGal gravity low over the structure indicating a subsurface low density body. Instead, the best fit is achieved for a bowl-shaped structure with a slight central rise as expected for an impact crater of this size in mainly sedimentary target. The structure can be either root-less (i.e., impact crater) or rooted with a narrow feeder dyke with relatively higher magnetic susceptibility and density (i.e., volcanic maar crater). The geophysical signature, the solitary appearance, the predominantly sedimentary setting, and the comparably large size of the Tsenkher structure favor the impact crater alternative. However, until mineralogical/geochemical evidence for an impact is presented, the maar alternative remains plausible although exceptional as it would make the Tsenkher structure one of the largest in the world in an unusual setting for maar craters. [source] Rietveld analysis of X-ray powder diffraction patterns as a potential tool for the identification of impact-deformed carbonate rocksMETEORITICS & PLANETARY SCIENCE, Issue 11 2009Sarah A. Huson Entire XRD patterns, single peak profiles and Rietveld refined parameters of carbonate samples from the Sierra Madera impact crater, west Texas, unshocked equivalent samples from 95 miles north of the crater and the Mission Canyon Formation of southwest Montana and western Wyoming were used to evaluate the use of X-ray powder diffraction as a potential tool for distinguishing impact deformed rocks from unshocked and tectonically deformed rocks. At Sierra Madera dolostone and limestone samples were collected from the crater rim (lower shock intensity) and the central uplift (higher shock intensity). Unshocked equivalent dolostone samples were collected from well cores drilled outside of the impact crater. Carbonate rocks of the Mission Canyon Formation were sampled along a transect across the tectonic front of the Sevier and Laramide orogenic belts. Whereas calcite subjected to significant shock intensities at the Sierra Madera impact crater can be differentiated from tectonically deformed calcite from the Mission Canyon Formation using Rietveld refined peak profiles, weakly shocked calcite from the crater rim appears to be indistinguishable from the tectonically deformed calcite. In contrast, Rietveld analysis readily distinguishes shocked Sierra Madera dolomite from unshocked equivalent dolostone samples from outside the crater and tectonically deformed Mission Canyon Formation dolomite. [source] The Canyon Diablo impact event: Projectile motion through the atmosphereMETEORITICS & PLANETARY SCIENCE, Issue 1 2009Natalia ARTEMIEVA Its location in arid northern Arizona has been ideal for the preservation of the structure and the surviving meteoric material. The recovery of a large amount of meteoritic material in and around the crater has allowed a rough reconstruction of the impact event: an iron object 50 m in diameter impacted the Earth's surface after breaking up in the atmosphere. The details of the disruption, however, are still debated. The final crater morphology (deep, bowl-shaped crater) rules out the formation of the crater by an open or dispersed swarm of fragments, in which the ratio of swarm radius to initial projectile radius Cd is larger than 3 (the final crater results from the sum of the craters formed by individual fragments). On the other hand, the lack of significant impact melt in the crater has been used to suggest that the impactor was slowed down to 12 km/s by the atmosphere, implying significant fragmentation and fragments' separation up to 4 initial radii. This paper focuses on the problem of entry and motion through the atmosphere for a possible Canyon Diablo impactor as a first but necessary step for constraining the initial conditions of the impact event which created Meteor Crater. After evaluating typical models used to investigate meteoroid disruption, such as the pancake and separated fragment models, we have carried out a series of hydrodynamic simulations using the 3D code SOVA to model the impactor flight through the atmosphere, both as a continuum object and a disrupted swarm. Our results indicate that the most probable pre-atmospheric mass of the Meteor Crater projectile was in the range of 4.108to 1.2.109kg (equivalent to a sphere 46,66 m in diameter). During the entry process the projectile lost probably 30% to 70% of its mass, mainly because of mechanical ablation and gross fragmentation. Even in the case of a tight swarm of particles (Cd < 3), small fragments can separate from the crater-forming swarm and land on the plains (tens of km away from the crater) as individual meteorites. Starting from an impactor pre-atmospheric velocity of ,18 km/s, which represents an average value for Earth-crossing asteroids, we find that after disruption, the most probable impact velocity at the Earth's surface for a tight swarm is around 15 km/s or higher. A highly dispersed swarm would result in a much stronger deceleration of the fragments but would produce a final crater much shallower than observed at Meteor Crater. [source] Validation of numerical codes for impact and explosion cratering: Impacts on strengthless and metal targetsMETEORITICS & PLANETARY SCIENCE, Issue 12 2008E. PIERAZZO When properly benchmarked and validated against observation, computer models offer a powerful tool for understanding the mechanics of impact crater formation. This work presents results from the first phase of a project to benchmark and validate shock codes. A variety of 2D and 3D codes were used in this study, from commercial products like AUTODYN, to codes developed within the scientific community like SOVA, SPH, ZEUS-MP, iSALE, and codes developed at U.S. National Laboratories like CTH, SAGE/RAGE, and ALE3D. Benchmark calculations of shock wave propagation in aluminum-on-aluminum impacts were performed to examine the agreement between codes for simple idealized problems. The benchmark simulations show that variability in code results is to be expected due to differences in the underlying solution algorithm of each code, artificial stability parameters, spatial and temporal resolution, and material models. Overall, the inter-code variability in peak shock pressure as a function of distance is around 10 to 20%. In general, if the impactor is resolved by at least 20 cells across its radius, the underestimation of peak shock pressure due to spatial resolution is less than 10%. In addition to the benchmark tests, three validation tests were performed to examine the ability of the codes to reproduce the time evolution of crater radius and depth observed in vertical laboratory impacts in water and two well-characterized aluminum alloys. Results from these calculations are in good agreement with experiments. There appears to be a general tendency of shock physics codes to underestimate the radius of the forming crater. Overall, the discrepancy between the model and experiment results is between 10 and 20%, similar to the inter-code variability. [source] The effect of target lithology on the products of impact meltingMETEORITICS & PLANETARY SCIENCE, Issue 12 2008G. R. OSINSKI Impact events generate pressures and temperatures that can melt a substantial volume of the target; however, there remains considerable discussion as to the effect of target lithology on the generation of impact melts. Early studies showed that for impacts into crystalline targets, coherent impact melt rocks or "sheets" are formed with these rocks often displaying classic igneous structures (e.g., columnar jointing) and textures. For impact structures containing some amount of sedimentary rocks in the target sequence, a wide range of impact-generated lithologies have been described, although it has generally been suggested that impact melt is either lacking or is volumetrically minor. This is surprising given theoretical constraints, which show that as much melt should be produced during impacts into sedimentary targets. The question then arises: where has all the melt gone? The goal of this synthesis is to explore the effect of target lithology on the products of impact melting. A comparative study of the similarly sized Haughton, Mistastin, and Ries impact structures, suggests that the fundamental processes of impact melting are basically the same in sedimentary and crystalline targets, regardless of target properties. Furthermore, using advanced microbeam analytical techniques, it is apparent that, for the structures under consideration here, a large proportion of the melt is retained within the crater (as crater-fill impactites) for impacts into sedimentary-bearing target rocks. Thus, it is suggested that the basic products are genetically equivalent but they just appear different. That is, it is the textural, chemical and physical properties of the products that vary. [source] Archaeabacterial lipids in drill core samples from the Bosumtwi impact structure, GhanaMETEORITICS & PLANETARY SCIENCE, Issue 11 2008Marina ESCALA The Bosumtwi crater in Ghana (West Africa) is a relatively young (1.07 Myr) structure with a rim-to-rim diameter of about 10.5 km. In a preliminary study targeting the subsurface microbial life in the impact structure, seven samples of the impact breccia from the central uplift of the Bosumtwi crater were analyzed for the presence of typical archaeal membrane-lipids (GDGTs). These have been detected in four of the samples, at a maximum depth of 382 m below the lake surface, which is equivalent to 309 m below the surface sediment. The concentration of the GDGTs does not show a trend with depth, and their distribution is dominated by GDGT-0. Possible origins of these lipids could be related to the soils or rocks predating the impact event, the hydrothermal system generated after the impact, or due to more recent underground water [source] Geochemistry of Darwin glass and target rocks from Darwin crater, Tasmania, AustraliaMETEORITICS & PLANETARY SCIENCE, Issue 3 2008Kieren T. Howard Target rocks at Darwin crater are quartzites and slates (Siluro-Devonian, Eldon Group). Analyses show 2 groups of glass, Average group 1 is composed of: SiO2 (85%), Al2O3 (7.3%), TiO2 (0.05%), FeO (2.2%), MgO (0.9%), and K2O (1.8%). Group 2 has lower average SiO2 (81.1%) and higher average Al2O3 (8.2%). Group 2 is enriched in FeO (+1.5%), MgO (+1.3%) and Ni, Co, and Cr. Average Ni (416 ppm), Co (31 ppm), and Cr (162 ppm) in group 2 are beyond the range of sedimentary rocks. Glass and target rocks have concordant REE patterns (La/Lu = 5.9,10; Eu/Eu* = 0.55,0.65) and overlapping trace element abundances. 87Sr/86Sr ratios for the glasses (0.80778,0.81605) fall in the range (0.76481,1.1212) defined by the rock samples. ,-Nd results range from ,13.57 to ,15.86. Nd model ages range from 1.2,1.9 Ga (CHUR) and the glasses (1.2,1.5 Ga) fall within the range defined by the target samples. The 87Sr/86Sr versus 87Rb/86Sr regression age (411 ± 42 Ma) and initial ratio (0.725 ± 0.016), and the initial 43Nd/144Nd ratio (0.51153 ± 000011) and regression age (451 ± 140 Ma) indicate that the glasses have an inherited isotopic signal from the target rocks at Darwin crater. Mixing models using target rock compositions successfully model the glass for all elementsexcept FeO, MgO, Ni, Co, and Cr in group 2. Mixing models using terrestrial ultramafic rocks fail to match the glass compositions and these enrichments may be related to the projectile. [source] Dust from comet Wild 2: Interpreting particle size, shape, structure, and composition from impact features on the Stardust aluminum foilsMETEORITICS & PLANETARY SCIENCE, Issue 1-2 2008A. T. Kearsley By comparison to laboratory shots of known particle dimensions and density, using the same velocity and incidence geometry as the Stardust Wild 2 encounter, we can derive size and mass of the cometary dust grains. Using scanning electron microscopy (SEM) of foil samples (both flown on the mission and impacted in the laboratory) we have recognized a range of impact feature shapes from which we interpret particle density and internal structure. We have documented composition of crater residues, including stoichiometric material in 3 of 7 larger craters, by energy dispersive X-ray microanalysis. Wild 2 dust grains include coarse (>10 ,m) mafic silicate grains, some dominated by a single mineral species of density around 3,4 g cm,3 (such as olivine). Other grains were porous, low-density aggregates from a few nanometers to 100 ,m, with an overall density that may be lower than 1 g cm,3, containing mixtures of silicates and sulfides and possibly both alkali-rich and mafic glass. The mineral assemblage is very similar to the most common species reported from aerogel tracks. In one large aggregate crater, the combined diverse residue composition is similar to CI chondrites. The foils are a unique collecting substrate, revealing that the most abundant Wild 2 dust grains were of sub-micrometer size and of complex internal structure. Impact residues in Stardust foil craters will be a valuable resource for future analyses of cometary dust. [source] Post-impact structural crater modification due to sediment loading: An overlooked processMETEORITICS & PLANETARY SCIENCE, Issue 11 2007Filippos Tsikalas The analysis demonstrates that the geometry and the structural and stratigraphic relations of post-impact strata provide information about the amplitude, the spatial distribution, and the mode of post-impact deformation. Reconstruction of the original morphology and structure for the Mjølnir, Chicxulub, and Bosumtwi craters demonstrates the long-term subsidence and differential compaction that takes place between the crater and the outside platform region, and laterally within the crater structure. At Mjølnir, the central high developed as a prominent feature during post-impact burial, the height of the peak ring was enhanced, and the cumulative throw on the rim faults was increased. The original Chicxulub crater exhibited considerably less prominent peak-ring and inner-ring/crater-rim features than the present crater. The original relief of the peak ring was on the order of 420,570 m (currently 535,575 m); the relief on the inner ring/crater rim was 300,450 m (currently ,700 m). The original Bosumtwi crater exhibited a central uplift/high whose structural relief increased during burial (current height 101,110 m, in contrast to the original height of 85,110 m), whereas the surrounding western part of the annular trough was subdued more that the eastern part, exhibiting original depths of 43,68 m (currently 46 m) and 49,55 m (currently 50 m), respectively. Furthermore, a quantitative model for the porosity change caused by the Chesapeake Bay impact was developed utilizing the modeled density distribution. The model shows that, compared with the surrounding platform, the porosity increased immediately after impact up to 8.5% in the collapsed and brecciated crater center (currently +6% due to post-impact compaction). In contrast, porosity decreased by 2,3% (currently ,3 to ,4.5% due to post-impact compaction) in the peak-ring region. The lateral variations in porosity at Chesapeake Bay crater are compatible with similar porosity variations at Mjølnir crater, and are considered to be responsible for the moderate Chesapeake Bay gravity signature (annular low of ,8 mGal instead of ,15 mGal). The analysis shows that the reconstructions and the long-term alterations due to post-impact burial are closely related to the impact-disturbed target-rock volume and a brecciated region of laterally varying thickness and depth-varying physical properties. The study further shows that several crater morphological and structural parameters are prone to post-impact burial modification and are either exaggerated or subdued during post-impact burial. Preliminary correction factors are established based on the integrated reconstruction and post-impact deformation analysis. The crater morphological and structural parameters, corrected from post-impact loading and modification effects, can be used to better constrain cratering scaling law estimates and impact-related consequences. [source] | |||||||||||||||||||||||||||||||