Round Stones Research Articles

Dead Woman's Pass

Dead Woman's Pass Kaia Preus The sun cut over the top of the Andes, and Gina palmed the sweat off her forehead. She yanked on her backpack straps, hoisting the bag higher on her shoulders. Behind her, some of the other hikers in her group talked above the slap of their feet on the rounded stone. Gina hiked alone. When she was young, Gina's mother had spent Saturdays paging through National Geographic magazines at their worn kitchen table and saying, "I would love to go there. And there." Her bitten-down nails brushed across the pictures. "What I'd really like to do is hike the Inca Trail to Macchu Picchu like my mother did." Gina's mother sighed then, closed the magazine, and said, "Maybe when you graduate from college, we'll go." She turned toward the window where their soybean crops extended all the way to the horizon. When Gina was younger, she thought her mother would eventually go to Macchu Picchu, that it was just a matter of money or time, and that she would bring Gina along. They could figure out the airport together, be brave and get lost in a new city, stumble into a hole-in-the-wall restaurant and drink pisco sours, like she had seen people do on the Travel Channel. They would hike the Inca Trail together, whisper goodnight in their shared tent atop a mountain, wake up to the sunrise and think about the fact that Gina's grandmother had hiked this very trail. But then, a year ago, just after Gina turned twenty-three, a sleeping semi-truck driver swerved into the family pick-up and Gina's mother died two days later in the Blue Earth County Hospital, the same hospital where she had been born. Gina jabbed her pole into a space between rocks and pulled her body up a few more inches. She breathed heavily through her mouth and took small steps. She had learned that if she made her stride wider, she would tire more quickly and have to take breaks, after which it was hard to start back up again. It was better to minimize the stretch and burn of her leg muscles by going slowly. Her heart pounded and she listened to the sound of it mingling with her steady, heavy breath. When she had a clear understanding of where she would place her feet over the next few steps, she looked up to the mountain ahead of her, deep green and quiet. These mountains made her feel miniscule in a way that the plains of her childhood could not. If she looked carefully, she could see the tiny red and yellow and blue dots of other hikers' jackets far above her on the trail. To think that she had to make it that far today, and then farther, was almost enough to make her stop walking altogether. She felt a hand on her shoulder. Javier, the trek's second guide, smiled at her out of the thin neck scarf he wore to protect himself from the sun. "Hey, Javier," Gina said. "How are you doing, Gina?" Javier spoke normally. His breath was not labored. Gina suspected that he could run up and down this mountain in half the time it would take her to only make it up. His ancestors had carried food and stones across these mountains five centuries ago. This landscape was in [End Page 21] his blood. Gina pictured the outline of the mountains as the electronic peaks and valleys of her mother's heartbeat on the hospital monitor. The plains were Gina's homeland. A flatline. For a moment, Gina could hear the long, screeching beep of her mother's heart giving up. She could see the face that had leaned over her pillow at night with goodnight kisses turn slack and bruised the colors of dusk. "I'm fine," said Gina. "This mountain is kicking my ass. Much harder than yesterday." Javier giggled his high-pitched, wheezy laugh. "You're doing well," he said. "The second day of the hike, this section of trail up to Dead Woman's Pass, is the hardest day of...

Middle Stone Age Ochre Processing and Behavioural Complexity in the Horn of Africa: Evidence from Porc-Epic Cave, Dire Dawa, Ethiopia.

Ochre is a common feature at Middle Stone Age (MSA) sites and has often been interpreted as a proxy for the origin of modern behaviour. However, few ochre processing tools, ochre containers, and ochre-stained artefacts from MSA contexts have been studied in detail within a theoretical framework aimed at inferring the technical steps involved in the acquisition, production and use of these artefacts. Here we analyse 21 ochre processing tools, i.e. upper and lower grindstones, and two ochre-stained artefacts from the MSA layers of Porc-Epic Cave, Dire Dawa, Ethiopia, dated to ca. 40 cal kyr BP. These tools, and a large proportion of the 4213 ochre fragments found at the site, were concentrated in an area devoted to ochre processing. Lower grindstones are made of a variety of raw materials, some of which are not locally available. Traces of use indicate that different techniques were employed to process ochre. Optical microscopy, XRD, μ-Raman spectroscopy, and SEM-EDS analyses of residues preserved on worn areas of artefacts show that different types of ferruginous rocks were processed in order to produce ochre powder of different coarseness and shades. A round stone bearing no traces of having been used to process ochre is half covered with residues as if it had been dipped in a liquid ochered medium to paint the object or to use it as a stamp to apply pigment to a soft material. We argue that the ochre reduction sequences identified at Porc-Epic Cave reflect a high degree of behavioural complexity, and represent ochre use, which was probably devoted to a variety of functions.

Design of Minimum Cost Earthen Channels Having Side Slopes Riveted With Different Types of Riprap Stones and Unlined Bed by Using Particle Swarm Optimization

AbstractSeveral design alternatives for a trapezoidal earthen channel whose side slopes are riveted with riprap stones and bottom is unlined were analysed to compare the performance of different types of stones (round, sub‐round and sub‐angular, and angular) for minimum cost and performance effectiveness. Particle swarm optimization (PSO) algorithm was implemented to determine the minimum cost channel in contrast with earlier alternatives relating to the most hydraulically efficient sections. Both clear water and sediment‐laden flow conditions were applied to investigate the effect of flowing water characteristics on optimality, which is not available in the literature. Optimal design of channels incorporating land acquisition cost is scanty; therefore, land cost was also included in the objective function. In addition to the design of a channel without freeboard, different freeboard scenarios, including depth‐dependent equations, were applied to assess the impact of freeboard provision methodologies on optimal channel dimensions and cost. It was found that the channels having angular riprap revetment for sediment‐laden flow conditions offered the minimum cost of construction, with sub‐round and sub‐angular, and round stones coming next in sequence, and the freeboard provisions also impacted the channel shape, dimensions and cost. Copyright © 2016 John Wiley & Sons, Ltd.

A STONE ABRASIVE TILE FROM CHEREMKHOVA, WESTERN AMUR REGION

A stone abrasive tile excavated by A.V. Machinsky in 1940 at an Early Medieval site at Cheremkhovo, Amur Region, is described. Judging by the results of the experimental use-wear and technological analyses, the tile was used to polish round stone beads. In East Asia, such specialized tools first appeared in the early Neolithic (Novopetrovka culture) and were still employed in the Early Iron Age and during the Middle Ages.

Petrology of green round stone axes excavated from the Sannai-Maruyama special historical site, Japan, with special reference to the significance to address the source rock of the axes

Petrology of green round stone axes excavated from the Sannai-Maruyama special historical site, Japan, with special reference to the significance to address the source rock of the axes

Impacted and Fractured Biliary Basket: A Second Basket Rescue Technique.

A 59-year-old woman was treated with ERCP, ES, and biliary plastic stent, for large and multiple common bile duct stones. During a second ERCP basket extraction was impacted with a round entrapped stone. The basket handle was cut off; a metal sheath of extraendoscopic lithotriptor was advanced over the basket. The mechanical lithotripsy was complicated with basket traction wires fracturing, without breakage of the stone. A rescue standard basket was pushed until it caught the basket/stone complex. Using this method disengagement of the whole fractured basket/stone complex was achieved without need of surgery. It is the third case reported in the English literature.

Arhitectura epocii Latene din Munții Șureanu (Sebeșului). O analiză metodologică / The Architecture of the Late Iron Age in the Șureanu (Sebeșului) Mountains. A Methodological Approach

Arhitectura epocii Latene din Munții Șureanu (Sebeșului). O analiză metodologică / The Architecture of the Late Iron Age in the Șureanu (Sebeșului) Mountains. A Methodological Approach

Anisotropy is Everywhere, to See, to Measure, and to Model

Anisotropy is everywhere. Isotropy is rare. Round stones are collectors’ items, and any almost cubic blocks are photographed, as they are the exception. The reasons for rock masses to frequently exhibit impressive degrees of anisotropy, with properties varying with direction of observation and measurement, are clearly their varied geological origins. Origins may provide distinctive bedding cycles in sedimentary rocks, distinctive flows and flow-tops in basalts, foliation in gneisses, schistosity in schists and cleavage in slates, and faults through all the above. We can add igneous dykes, sills, weathered horizons, and dominant joint sets. Each of the above are rich potential or inevitable sources of velocity, modulus, strength and permeability anisotropy—and inhomogeneity. The historic and present-day stress anisotropy provides a wealth of effects concerning the preferentially oriented jointing, with its reduced roughness and greater continuity. High stress may also have induced oriented micro-cracks. All the above reinforce disbelief in the elastic-isotropic-continuum or intact-medium-based assumptions promoted by commercial software companies and used by so many for modelling rock masses. RQD and Q are frequently anisotropic as well, and Q is anisotropic not just because of RQD. The authors, therefore, question whether the a priori assumption of homogeneous-isotropic-elastic behaviour has any significant place in the scientific practice of realistic rock mechanics.

Role of hepatobiliary tract anatomy and morphology of gallstones in causation of acute pancreatitis

Introduction: Gall stone disease is a common cause of acute pancreatitis. At present the pattern of gall stones complication are largely unpredictable. Little research has been done to identify gall stone morphology and biliary tract anatomy in the causation of gall stone induced pancreatitis. Aims and Objectives: The present study was done at IGMC Shimla to study the relationship of gallstone characteristics to the risk of gall stone pancreatitis and to compare and evaluate the biliary tract anatomy in patients of gall stone induced pancreatitis and cholelithiasis by MRCP. Materials and Methods: The prospective study included 25 patients each of symptomatic cholelithiasis and gall stone induced pancreatitis divided into Group A and Group B respectively. All the patients were subjected to MRCP preoperatively. All the patients were operated by laproscopic or open method. Postoperatively the gall stone were collected and analyzed. Results: On MRCP- In Group A Single calculus was present in 11 (44%) patients and 1 (4%) patients had associated sludge, 14 (56%) patients had multiple calculi and 3 (44%) patients had associated sludge.In Group B 22 (88%) patients had multiple calculi and 16 (56%) patients had associated sludge, 3 (12%) patients had single stone, and 2 (8%) patients had associated sludge. In Group A, CBD stones were seen in 3 (12%) patients, cystic duct diameter ranged from 3 mm to 5.2 mm, CBD diameter ranged from 5 mm to 9 mm and pancreatic duct diameter ranged from 2.7 mm to 4 mm.In Group B, CBD stones were seen in 7 (28%) patients, cystic duct diameter ranged from 4 mm to 6.4 mm, CBD diameter ranged from 5 mm to 12 mm and pancreatic duct diameter ranged from 2.6 mm to 4.8 mm In Group A, Common channel was seen in 8 (32%) patients. In Group B, Common channel was seen in 18 (72%) patients Gall Stone Morphology- In Group A, Single calculus present in 11 (44%) patients and 1 (4%) patient had associated sludge. Multiple calculi present in 14 (56%) patients and 3 (12%) patients had associated sludge. In Group B, Single calculus present in 3 (12%) patients and 2 (8%) patients had associated sludge. In group A, 15 (60%) patients had round stones and 14 (56%) patients had multifaceted stones and 6 (24%) patients had associated sludge. In Group B, 5 (20%) patients had round stones and 14 (56%) patients has multifaceted stones and 6 (24%) patients had associated sludge. Sludge <2 mm diameter was present in 6 patients each in Group A and B. Weight ranged from 2 to 3.8 gm in Group A and in Group B from 1.6 to 3.25gm. Conclusion: The present study clearly established an association between multiple, multifaceted stones, sludge, wide cystic duct and presence of common channel with increased incidence of Gallstone induced pancreatitis, MRCP also proved to be an excellent diagnostic modality in Gall stone induced pancreatitis.

A new specimen of large-bodied basal Enantiornithine Bohaiornis from the Early Cretaceous of China and the inference of feeding ecology in Mesozoic birds

A new specimen of Bohaiornis guoi from the Jiufotang Formation, comprising a nearly complete skeleton, sheds light on enantiornithine morphological variation and ecological specialization. The new specimen was collected from near Lamadong Village in Liaoning Province, which is the same area where the sub-adult holotype specimen was reported. It provides new information on the cranial and pectoral girdle anatomy of the species, e.g., broad nasal, strikingly robust acromion, medially curved acrocoracoid process. In contrast to the holotype, the newly referred specimen has small rounded stones in the thoracic region that in other extinct taxa has been interpreted as direct evidence of diet. Direct evidence of diet is so far unknown in other Enantiornithes. Specifically the lack of “stomach stones” or gastroliths in enantiornithines despite their excellent fossil record has been proposed to be related to their insectivorous diet as well as to their arboreal ecology. We hypothesize that cranial morphology as well as the number and shape of the preserved stones in Bohaiornis may be most consistent with a raptorial ecology previously unknown for Enantiornithes and considered rare for Avialae. While rostrum shape has a strong relationship to feeding ecology in living birds, in basal avialan birds most diversity is in dental morphology, number, and distribution of the teeth.

In Search of First Contact: The Vikings of Vinland, the peoples of the Dawnland, and the Anglo-American anxiety of discovery by Annette Kolodny (review)

Reviewed by: In Search of First Contact: The Vikings of Vinland, the peoples of the Dawnland, and the Anglo-American anxiety of discovery by Annette Kolodny Christine DeLucia In Search of First Contact: The Vikings of Vinland, the peoples of the Dawnland, and the Anglo-American anxiety of discovery By Annette Kolodny. Durham, North Carolina: Duke University Press, 2012. The presence of “Northmen” in the annals of North American history has often been shadowy, more subject to romance than rigorous investigation, Annette Kolodny demonstrates in this wide-ranging study of early European encounters with the Americas. Yet the experiences of the Norse in Vinland and related sites, circa AD 1000, deserve attention because they illuminate under-recognized dimensions of “contacts” between Indigenous peoples and would-be colonizers. They also suggest how contemporary mythologies have mobilized this past for cultural and political purposes, turning actual mariners and settlers into “plastic Viking[s]” (204): figures that could be molded into suitable, often heroic, forms by later residents of the United States, who worried intensely about origins, race and the legitimacy of their claims to place. Kolodny approaches the topic through literary studies, but draws upon interdisciplinary methods to combine textual analyses with findings of archaeology, ethnohistory, and Native studies. Following an introduction about controversies surrounding the concept of “prehistory” in the Americas, the book focuses on three aspects of Norse history, mythologizing and indigenous contacts. The first conducts close readings of Icelandic sagas, notably The Greenlanders’ Saga and Eirik the Red’s Saga, probing their internal narrative structures and possible historical referents. This section hones in on passages that narrate encounters with “Skraelings,” as the Norse characterized Indigenous peoples of Atlantic North America, and the presence of violence in these uncertain initial encounters. It also hypothesizes about which part of the Atlantic coastline may have been the location of Vinland (from Canadian maritime areas to sites further south), putting the sagas in conversation with archaeological and environmental assessments. As Kolodny notes, these sagas transformed over time because of natural morphing during oral storytelling, as well as editorial emendations by scribes who recorded them, sometimes at great temporal removes from the actual events. The second section examines how historians, antiquarians, literary luminaries and the public in the nineteenth-century United States cultivated fascination with Norse antecedents. Particularly during the American Romantic period, as commentators sought historicity for the young republic on par with Europe’s heritage, interest in these early Norse explorations spiked. Attention frequently fixated on material remnants that seemed to bespeak evidence of Norse presence. In southern New England, for example, human remains and burial items unearthed in Fall River, Massachusetts, became widely interpreted as Viking. Similarly, a round stone tower in Newport, Rhode Island, became interpreted as structural proof of Viking habitations. (Modern archaeological and historical investigations largely debunk those claims.) Kolodny situates these fascinations with origin stories within growing Anglo-American anxiety about a rising tide of immigrants from southern Europe, often denigrated as inferior to those of Anglo-Saxon descent, and concludes that playing up Norse “discoveries” satisfied nativist desires for primacy in the US nation, and in the rapidly changing region of New England specifically. Thus the Norse, and particularly Leif Eiriksson, challenged Columbus’s perch on the historical and mythic pedestal. As the 1893 Chicago World’s Fair developed public representations of American origins, these dueling narratives unfolded on a major stage. The book’s third section journeys across the Native Northeast to assess how Indigenous communities’ often closely held traditions may provide additional reflections on early Norse/Native encounters. Here the study ponders sources such as petroglyphs (inscriptions/incisions on rocks) that may convey Indigenous views of the earliest European settlements, as well as tribal oral traditions that relate accounts of contacts with “strangers.” Altogether, Kolodny finds that these oral traditions (from modern-day culture-keepers in communities including the Mi’kmaq, Passamaquoddy, Penobscot and Western Abenaki) are difficult to judge as firm evidence that these communities remember Norse encounters. The evolving quality of oral accounts in response to shifting circumstances and narrative needs, and the possible conflation of multiple European encounters, perhaps makes these sources less useful for providing details about the Norse specifically...

Computational fluid dynamics analysis of salivary flow and its effect on sialolithogenesis.

Sialolithiasis is a common disease caused by intraductal stones, formed by reduction in salivary flow, salivary stagnation, and metabolic events. We used computational fluid dynamics to investigate changes in salivary flow field around parotid stones of different shapes. Three-dimensional configurations of the Stensen's duct were reconstructed from computed tomography sialographic images. Fluid dynamics modeling was used to analyze the salivary flow field around stones under unstimulated and stimulated conditions. The majority of sialoliths were oval-shaped (59/98), followed by irregular (24/98) and round (15/98). Salivary velocity was significantly higher around streamlined stones, compared with round (P=0.013) and oval (P=0.025) types. Changes in salivary flow field around sialoliths were found to affect the pattern of mineral deposition in saliva. The area of low velocity around the round stone was double the size observed around the streamlined stone during the unstimulated state, whereas in the stimulated state, local vortexes were formed on the downstream side of round and oval stones. Salivary flow field around sialoliths plays an important role in the progression of multicentric stones, and analysis of the salivary dynamics during sialolithiasis may provide deeper understandings of the condition and aid in developing successful treatment strategies.

Occupational accident rate in olive oil mills

Problem This paper aims at examining the occupational accident rate in Spain in the olive oil mill industry. These mills produce olive oil by physical or mechanical, but not chemical procedures. Although Spain is the leading olive oil producer in the world with 1,200,000 tons/year and over 25% of the world olive farming area, the occupational accident rate in this sector has been little studied in the relevant scientific literature. Method Our study analyses all occupational accidents which occurred during 2004–2009, with or without sick leave, at 90 Andalusian olive oil mills covered by one of the biggest state insurance companies for accidents at work and occupational diseases (within the Spanish Social Security system). Results and discussion Slips or trips are the most frequent cause of occupational accidents in this sector, accounting for 14.86% of the cases. In second position, incorrectly coordinated bodily movements account for almost 13.51% of the accidents. Falls from height, 12.2% of the cases, are also statistically noteworthy. As for the seriousness of the injuries, entrapments are particularly important, since in 2.70% of the cases they result in the traumatic amputation of a part of the body. The analysis of accidents without sick leave reveals that a high number of incidents are caused by contact of the skin and eyes with hazardous substances (20% of the cases) and 10% of them involve superficial injuries. Impact on the industry This paper provides a clear and updated image of the accident rate in Spanish olive oil mills and can be a useful tool for the design and adequate adjustment of the management systems implemented in these plants to guarantee a satisfactory level of occupational health and safety by means of more efficient planning and monitoring of measures intended to reduce professional risks and improve working conditions. Recommendations Given not only the high incidence of falls on the same level and the potential seriousness of falls from different levels, but also the small, round fruit involved, with a high oil content and a hard round stone, it is extremely important to design and implement safe working procedures and specifically train both operatives and managers in charge of the tidiness, cleanliness and regular control of the premises and operations. The analysis of the accidents not requiring sick leave (mostly cases of contact with hazardous substances on the skin or eyes, or superficial injuries) clearly reveals that the use of suitable personal protective equipment and the relevant training are crucial issues.

Assessing past agrobiodiversity of Prunus avium L. (Rosaceae): a morphometric approach focussed on the stones from the archaeological site Hôtel-Dieu (16th century, Tours, France)

Abundant and diverse Prunus fruitstone remains from cherries, plums, sloes, peaches, etc. are frequently recovered from archaeological waterlogged contexts such as wells, latrines, lake dwellings etc. in Europe. The distinction between most of the Prunus species, based on traditional morphological characters of the fruit stones, is usually not problematic. However the discrimination between P. avium L., P. cerasus L. and related cherry species, based on classical criteria alone, often turns out to be ambiguous because of the increasing number of varieties which have been bred since Roman times. By combining geometric and traditional morphometrical approaches, the overall variation in shape and size of stones from French and Swiss excavations dating from the 1st century to the 16th century a.d. were assessed. Among these important archaeobotanical data, the detailed examination of 100 waterlogged stones from the 16th century Hotel-Dieu cesspit at Tours, France, revealed that the morphological diversity is structured into two distinct morphotypes which diverge mainly according to geometrical features. Finally, the comparison between morphological features of these well-preserved archaeological stones and modern reference material including P. avium, P. cerasus and P. × gondouinii, suggests that these two morphotypes, which have been initially attributed to P. avium (long stones) and P. avium/cerasus (rounded stones) according to traditional morphological parameters, would correspond to two different cultivated varieties, both belonging to Prunus avium. Results presented in this work constitute new and preliminary data obtained during the development of this project that throw light on morphological variability and biosystematic aspects.

Keeping Watch as the Old Kingdom Crumbled

The round stone fort at Ras Budran on the southern Sinai Peninsula hints at the precariousness of Egypt's Old Kingdom, suggesting an increasingly desperate trading and military strategy in the waning days of the 22nd century B.C.E., an excavator reported at the meeting.

History of Ecological Sciences, Part 37: Charles Darwin's Voyage on the Beagle

History of Ecological Sciences, Part 37: Charles Darwin's Voyage on the Beagle

A spatio‐temporal analysis of ‘Oro cult marae in the’ Opunohu Valley, Mo'orea, Society Islands

ABSTRACT A new war cult dedicated to the god 'Oro emerged in late prehistory in the Society Islands and was linked to shifts in temple architecture, religious rituals, and sacred regalia. Legends suggest that this war cult developed in the Leeward Islands and was translocated to the Windward group prior to European contact. This article summarizes ethnohistoric data for the 'Oro war cult, including its relationship to new temple styles in the Windward group constructed from worked rounded stones. Such temples are found in both inland and coastal contexts. Extant chronological data on Windward marae of the 'Oro style are synthesized. A new spatio‐temporal case study of four 'Oro style temples from the 'Opunohu Valley, Mo'orea demonstrates considerable variability in temple morphology and chronology. This is linked to differences among socio‐political maneuverings of high status lineage chiefs versus lower status lineage chiefs in the 'Opunohu Valley and perhaps to functional variation among the types of 'Oro style marae structures found in inland contexts. The new chronology suggests a rapid translocation of the 'Oro style war cult into the Windward group, somewhat earlier than previous archaeological work had suggested.

What's Inside?: Fascinating Structures around the World (review)

Reviewed by: What's Inside?: Fascinating Structures around the World Elizabeth Bush Laroche, Giles What's Inside?: Fascinating Structures around the World; written and illus. by Giles Laroche. Harcourt, 200940p ISBN 978-0-618-86247-4$17.00 R Gr. 3-6 While the titular question and picture-book format suggest a work for primary-schoolers, Laroche deploys the guessing-game structure and fabulously detailed collages to intrigue an older set of readers, particularly those with a budding interest in architecture. He starts off pretty easy, with an archaeologist breaking through the doorway "at the end of a long underground passageway": "What's inside?" Lots of kids will recognize Howard Carter, or at least know there's a mummy tomb on the next page. But how many will correctly guess that there's a jaguar throne inside the stepped pyramid, an entire city beyond a stone gate, or farm animals beneath the "squat wooden cupola" in a round stone building in New England? Even the identifiable structures hold visual surprises, with Laroche providing intricate interiors for each spread and a sidebar of geographical and statistical data for the edifice. A glossary of architectural terms is appended, each with a thumbnail picture of a building sporting that feature, and a partial list of Laroche's sources are included. This is an obvious draw for viewers who delight in fussy, finicky detail, and also an inspiration for kids with scissors, paper, and patience. [End Page 368] Copyright © 2009 The Board of Trustees of the University of Illinois

Countinuous and discrete models for abrasion processes

The origin of the shapes of stones and other particles formed by water or wind has always attracted the attention of geologists and mathematicians. A classical model of abrasion due to W. J. Firey leads to a geometric partial differential equation representing the continuum limit of the process. This model predicts convergence to spheres from an arbitrary initial form; analogously, the two-dimensional version of the model predicts convergence to circles. The shapes of real stones are, however, not always round. Most notably, coastal pebbles tend to be smooth but somewhat flat, and ventifacts (e.g. pyramidal dreikanters) often have completely different shapes with sharp edges. Inspired by Firey´s results, a new PDE is derived in this paper, which not only appears to be a natural mathematical generalization of Firey´s PDE, but also represents the continuum limit of a genezalized abrasion model based on recurrent loss of material due to collisions of nearby pebbles. We also introduce a related, mezo-scale discre te random model which is ideally suited for analyzing wear processes in specific geometric scenarios. Preliminary results suggest that our model is capable to predict a broad range of limit shapes: polygonal shapes with sharp edges develop due to sand blasting (big stone surrounded by infinitesimally small particles), round stones emerge due to collisions with relatively big stones, and flat shapes are the typical outcome in the intermediate case. The results show nice agreement with real data despite the model´s simplicity.

Migrating Intrathoracic Gallstone

We present the case of a 76-year-old man referred to our hospital with a round stone in central mediastinum and pneumomediastinum in chest radiography and computed tomography. He had a previous history of attempt of endoscopic retrievement of a gallstone that had caused a gastric outlet obstruction (Bouveret syndrome). To our knowledge, this is the first imaging description of mediastinal gallstone caused by esophagus perforation during complicated endoscopic lithotomy.