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Статті в журналах з теми "Surfaces of hard-to-make"
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van der Krogt, Marjolein M., Wendy W. de Graaf, Claire T. Farley, Chet T. Moritz, L. J. Richard Casius, and Maarten F. Bobbert. "Robust passive dynamics of the musculoskeletal system compensate for unexpected surface changes during human hopping." Journal of Applied Physiology 107, no. 3 (September 2009): 801–8. http://dx.doi.org/10.1152/japplphysiol.91189.2008.
Повний текст джерелаАнотація:
When human hoppers are surprised by a change in surface stiffness, they adapt almost instantly by changing leg stiffness, implying that neural feedback is not necessary. The goal of this simulation study was first to investigate whether leg stiffness can change without neural control adjustment when landing on an unexpected hard or unexpected compliant (soft) surface, and second to determine what underlying mechanisms are responsible for this change in leg stiffness. The muscle stimulation pattern of a forward dynamic musculoskeletal model was optimized to make the model match experimental hopping kinematics on hard and soft surfaces. Next, only surface stiffness was changed to determine how the mechanical interaction of the musculoskeletal model with the unexpected surface affected leg stiffness. It was found that leg stiffness adapted passively to both unexpected surfaces. On the unexpected hard surface, leg stiffness was lower than on the soft surface, resulting in close-to-normal center of mass displacement. This reduction in leg stiffness was a result of reduced joint stiffness caused by lower effective muscle stiffness. Faster flexion of the joints due to the interaction with the hard surface led to larger changes in muscle length, while the prescribed increase in active state and resulting muscle force remained nearly constant in time. Opposite effects were found on the unexpected soft surface, demonstrating the bidirectional stabilizing properties of passive dynamics. These passive adaptations to unexpected surfaces may be critical when negotiating disturbances during locomotion across variable terrain.
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Khellouki, A., J. Rech, and H. Zahouani. "Influence of the belt-finishing process on the surface texture obtained by hard turning." Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture 221, no. 7 (July 1, 2007): 1129–37. http://dx.doi.org/10.1243/09544054jem776.
Повний текст джерелаАнотація:
The belt-finishing process is a recent manufacturing technique in industry, the mechanisms and characteristics of which have not yet been fully explained. This paper attempts to make a contribution to the understanding of the consequences of the process on the surface roughness of surfaces prepared by hard turning. Abrasive film wear and contact parameters between grains and surfaces are analysed. The effects and significant interactions of the most influential belt-finishing parameters on the surface roughness are then investigated. It was shown that the applied force and the hardness of the roller have a great influence on the surface roughness. Furthermore, the film feed rate influences considerably the wear of grains and, as a consequence, this parameter has an important impact on the material removal mode and on the surface roughness.
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Rusu, Laura-Cristina, Lavinia Cosmina Ardelean, Adriana-Andreea Jitariu, Catalin Adrian Miu, and Caius Glad Streian. "An Insight into the Structural Diversity and Clinical Applicability of Polyurethanes in Biomedicine." Polymers 12, no. 5 (May 24, 2020): 1197. http://dx.doi.org/10.3390/polym12051197.
Повний текст джерелаАнотація:
Due to their mechanical properties, ranging from flexible to hard materials, polyurethanes (PUs) have been widely used in many industrial and biomedical applications. PUs’ characteristics, along with their biocompatibility, make them successful biomaterials for short and medium-duration applications. The morphology of PUs includes two structural phases: hard and soft segments. Their high mechanical resistance featuresare determined by the hard segment, while the elastomeric behaviour is established by the soft segment. The most important biomedical applications of PUs include antibacterial surfaces and catheters, blood oxygenators, dialysis devices, stents, cardiac valves, vascular prostheses, bioadhesives/surgical dressings/pressure-sensitive adhesives, drug delivery systems, tissue engineering scaffolds and electrospinning, nerve generation, pacemaker lead insulation and coatings for breast implants. The diversity of polyurethane properties, due to the ease of bulk and surface modification, plays a vital role in their applications.
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Hu, Yong, and David B. Bogy. "Effects of Laser Textured Disk Surfaces on a Slider’s Flying Characteristics." Journal of Tribology 120, no. 2 (April 1, 1998): 266–71. http://dx.doi.org/10.1115/1.2834421.
Повний текст джерелаАнотація:
Recently, laser texturing has captured the attention of head/media interface engineers in the hard disk drive industry because it provides precision in the landing zone placement while eliminating the transition zone of a mechanically textured landing zone. It also offers excellent tribological performance in terms of low CSS stiction and good durability. These advantages make it the solution of choice for high-end magnetic hard disk drives. This paper models the effects of laser bumps and laser textured disk surfaces on the Headway AAB slider’s flying characteristics. Two commonly used laser bump profiles (“Sombrero” and “Volcano” types) and various texture patterns are numerically generated in the simulator. The slider’s dynamic responses to these moving laser bumps and textures under two outer rail flying conditions are simulated, and the effects of various bump/texture parameters on the slider’s fly height, pitch, roll and their modulations are discussed. The laser texture mechanism is explained by examining the air bearing pressure profiles induced by the moving laser textures.
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Pascu, Doru Romulus, Ramona Monica Buzdugan, Aurel Valentin Bîrdeanu, Daniel Tihanov, and Emilia Binchiciu. "Structural Hardening of Excavator Teeth Used in Exploitation of Magmatic Rocks." Advanced Materials Research 1111 (July 2015): 246–51. http://dx.doi.org/10.4028/www.scientific.net/amr.1111.246.
Повний текст джерелаАнотація:
The teeth of specialized excavators used in exploitation of magmatic rocks are made by forging from alloyed steels having 3.4%Mn, and the value of hardness less than 38HRC. The usual working time is about 15,000 hours.This paper estimates the possibility to make a structural hardening of the excavator teeth using the deposition by welding of hard layers. These hard layers are obtained by using the electrodes type Cr-W-V-Ti, having the hardness between 48 and 50HRC. In these conditions, the austenitic hard structures with complex carbides of W, V, Ti are developed.The presence of the hard layers on the active surfaces of teeth, deposited using an homologated technology, will allow to increase the life time of these components with minimum 30% in usually working conditions.
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McKay, I., and T. A. Gillespie. "Bacterial Contamination of Children's Toys Used in a General Practitioner's Surgery." Scottish Medical Journal 45, no. 1 (February 2000): 12–13. http://dx.doi.org/10.1177/003693300004500104.
Повний текст джерелаАнотація:
General practitioners — and other healthcare professionals are encouraged to make their premises child friendly. One way of doing this is to provide toys for children to use. We looked at the appearance and bacterial colonisation of 50 toys after a busy morning surgery in an inner city general practice. The toys appeared generally unclean and 10% were contaminated by potential pathogens. Bacteria were cultured more frequently from soft toys than from hard toys (odds ratio 8.14; 95% confidence range 0.74 − 107.49). Although toys may appear to be physically dirty after use, the bacteria isolated from their surfaces are generally non-pathogenic to children with normal immune function and probably no worse than other objects in the environment. However, there does exist an appreciable (1 in 10) risk of cross-infection with the use of toys in a clinic. Toys with a hard surface are preferred as these are less likely to be contaminated and are more easily disinfected.
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Creton, Costantino, and Stanislav Gorb. "Sticky Feet: From Animals to Materials." MRS Bulletin 32, no. 6 (June 2007): 466–72. http://dx.doi.org/10.1557/mrs2007.79.
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AbstractMany insects and some larger animals, such as geckos, skinks, and tree frogs, can easily climb vertical walls and even walk on the ceiling. These abilities require a method to attach the feet strongly but reversibly to a variety of surfaces—smooth or rough, hydrophilic or hydrophobic, clean or containing contaminants. This issue of MRS Bulletin examines how fibrils, absorbed water layers, geometry, and other factors make reversible adhesion possible, and how this understanding might be applied to robots and other artificially created structures that can climb walls, walk on ceilings, and get to other hard-to-reach places.
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Gryadunov, Sergey S., and Vladimir V. Sivakov. "The Use of Surfacing Materials to Increase the Durability of Disc Harrow Working Elements." Engineering Technologies and Systems 31, no. 4 (December 30, 2021): 544–58. http://dx.doi.org/10.15507/2658-4123.031.202104.544-558.
Повний текст джерелаАнотація:
Introduction. For surface tillage operation there widely used disc harrows, working bodies of which are discs wearing out during operation. The wear intensity of discs depends on the wear resistance of their working surfaces, working modes and properties of the cultivated soil. It has been found that an effective way to increase the life of discs is surfacing them with wear-resistant materials. The aim of the work is to study the wear out of surfacing materials, which can be used to harden discs and to make recommendation for the use of these materials in the repair departments of agricultural enterprises. Materials and Methods. Surfacing with electrodes T-590 and powder wires PP-Np200Kh15S1GRT, VELTEK-N560.02 and PP-Np280Kh9F7SG4 were taken as test materials. For wear tests of materials in abrasive mass, there was used an apparatus to simulate the moisture content and composition (sandy loam or loam) of the soil. In the disk-pad tests, the effect of abrasive particle size, load and sliding friction velocity on the wear of the materials was studied. In field tests, wear of the disks made of 65G steel, surfaced toothed and solid disks were monitored. Results. Laboratory studies of the materials revealed the effect of soil moisture and composition, load, abrasive grit and sliding friction velocity on wear. The main factor determining the wear resistance of materials is their structural state. The indexes of wear resistance of surfacing were determined during the laboratory tests and confirmed by field tests. Discussion and Conclusion. Surfacing with flux-cored wire PP-Np280Kh9F7SG4 has the highest wear resistance of the studied materials. The technology of hard-facing disks with modern materials, in particular with flux-cored wire PP-Np280Kh9F7SG4, can be implemented in repair departments of agricultural enterprises when they have the equipment for hard-facing and sharpening of working surfaces.
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Santiago-Medina, P., P. A. Sundaram, and N. Diffoot-Carlo. "Titanium Oxide: A Bioactive Factor in Osteoblast Differentiation." International Journal of Dentistry 2015 (2015): 1–9. http://dx.doi.org/10.1155/2015/357653.
Повний текст джерелаАнотація:
Titanium and titanium alloys are currently accepted as the gold standard in dental applications. Their excellent biocompatibility has been attributed to the inert titanium surface through the formation of a thin native oxide which has been correlated to the excellent corrosion resistance of this material in body fluids. Whether this titanium oxide layer is essential to the outstanding biocompatibility of titanium surfaces in orthopedic biomaterial applications is still a moot point. To study this critical aspect further, human fetal osteoblasts were cultured on thermally oxidized and microarc oxidized (MAO) surfaces and cell differentiation, a key indicator in bone tissue growth, was quantified by measuring the expression of alkaline phosphatase (ALP) using a commercial assay kit. Cell attachment was similar on all the oxidized surfaces although ALP expression was highest on the oxidized titanium alloy surfaces. Untreated titanium alloy surfaces showed a distinctly lower degree of ALP activity. This indicates that titanium oxide clearly upregulates ALP expression in human fetal osteoblasts and may be a key bioactive factor that causes the excellent biocompatibility of titanium alloys. This result may make it imperative to incorporate titanium oxide in all hard tissue applications involving titanium and other alloys.
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Sohrabi, Mehri, Saeed Hesaraki, and Asghar Kazemzadeh. "Injectable Bioactive Glass/Polysaccharide Polymers Nanocomposites for Bone Substitution." Key Engineering Materials 614 (June 2014): 41–46. http://dx.doi.org/10.4028/www.scientific.net/kem.614.41.
Повний текст джерелаАнотація:
nanobioactive glasses are biocompatible and osteoconductive materials which can be mixed with solution of biocompatible polymers to make nanobiocomposite paste for hard and even soft tissue treatment. In this study, bioactive glass based on CaO-SiO2-P2O5 system was produced via sol-gel technique and mixed with a solution phase. The solution phase was a 1:1 mixture of 3% hyaluronic acid solution and 3% sodium alginate solution in v/v. Rheological behaviors of the paste in rotation and oscillation modes were measured. For surface reactivity measurements, the paste was immersed in simulated body fluid (SBF) for different intervals and then characterized by SEM. The paste exhibited a superior injectability even from syringes with too narrow tips. It was a thixotropic fluid with shear thinning behavior. The results of surface reactivity revealed precipitation of apatite phase on the paste surfaces meanwhile an appropriate structural stability was observed against disintegration (anti-washout behavior). It seems that this biocomposite paste is an appropriate alternative for injectable bone substitute materials.
Дисертації з теми "Surfaces of hard-to-make"
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Артюх, Павло Володимирович. "Розробка в CAD/CAM системи проектування технології обробки корпусних деталей". Master's thesis, КПІ ім. Ігоря Сікорського, 2020. https://ela.kpi.ua/handle/123456789/38719.
Повний текст джерелаАнотація:
Магістерська дисертація на тему «Розробка в САD/САМ системи проектування технології обробки корпусних деталей» містить в собі вступ, чотири розділи та список використаної літератури.
В даній магістерській дисертації основною метою є проектується корпусна деталь складної форми профілю, виходячи з цього в залежності від вибору траєкторії інструмента в подальшому це впливає на точність обробки та час .
За допомогою CAD/CAM систем було зроблено 3D модель деталі та сформована керуюча програма для її обробки. Розглянуто плюси САМ системи, так як ми могли за допомогою цієї системи використати декілька методів траєкторії руху інструменту, та визначати який з методів забезпечить продуктивність та точність , так як деталь відноситься до групи складних корпусних деталей , в результаті чого розроблений стартап- проект якій базується на підвищені продуктивності та точності в деталях складної форми профілю , і в результаті аналізу , проект можна запустити на ринок.Is master's Degree dissertation on a theme «Development in CAD/CAM of the system of planning of technology of treatment of cabinet-type details» contains an entry, four sections and list of the used literature. In this master's degree dissertation a primary purpose is the cabinet-type detail of difficult form of type is designed, coming from it depending on the choice of trajectory of instrument in future it influences on exactness of treatment and time . By CAD/CAM of the systems the 3d model of detail was done and control program is formed for its treatment. Pluses are considered systems, so as we could by this system use a few methods of trajectory of motion of instrument, and determine which from methods will provide the productivity and exactness, so as a detail behaves to the group of difficult cabinet-type details, as a result of what a startap- project is developed which is based on enhanceable the productivity and exactness in the details of difficult form of type, and as a result of analysis, a project can be started to the market.
Книги з теми "Surfaces of hard-to-make"
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Goan, Melanie Beals. A Simple Justice. University Press of Kentucky, 2020. http://dx.doi.org/10.5810/kentucky/9780813180175.001.0001.
Повний текст джерелаАнотація:
When the Declaration of Independence was signed by a group of wealthy white men in 1776, poor white men, African Americans, and women quickly discovered that the unalienable rights it promised were not truly for all. The Nineteenth Amendment eventually gave women the right to vote in 1920, but the change was not welcomed by people of all genders in politically and religiously conservative Kentucky. As a result, the suffrage movement in the Commonwealth involved a tangled web of stakeholders, entrenched interest groups, unyielding constitutional barriers, and activists with competing strategies. In A Simple Justice, Melanie Beals Goan offers a new and deeper understanding of the women's suffrage movement in Kentucky by following the people who labored long and hard to see the battle won. Women's suffrage was not simply a question of whether women could and should vote; it carried more serious implications for white supremacy and for the balance of federal and state powers -- especially in a border state. Shocking racial hostility surfaced even as activists attempted to make America more equitable. Goan looks beyond iconic women such as Susan B. Anthony and Elizabeth Cady Stanton to reveal figures whose names have been lost to history. Laura Clay and Madeline McDowell Breckinridge led the Kentucky movement, but they did not do it alone. This timely study introduces readers to individuals across the Bluegrass State who did their part to move the nation closer to achieving its founding ideals.
Частини книг з теми "Surfaces of hard-to-make"
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Bunker, Bruce C., and William H. Casey. "Bio-inspired Synthesis of Oxide Nanostructures." In The Aqueous Chemistry of Oxides. Oxford University Press, 2016. http://dx.doi.org/10.1093/oso/9780199384259.003.0015.
Повний текст джерелаАнотація:
Nature is capable of building magnificently intricate and detailed structures out of otherwise boring materials such as calcium carbonate and silica. Anyone who has taken their children to see dinosaurs at a Natural History museum or visited natural wonders such as the Petrified Forest in Arizona are familiar with the natural process called fossilization by which the tissues of dead organisms are eventually replicated by objects of stone. Most living organisms (including humans) are critically dependent on more deliberate and controlled biomineralization phenomena that lead to the production of all hard tissues, including our teeth and bones, seashells and diatom skeletons, egg shells, and the magnetic nanoparticles that provide homing devices from bacteria to birds. All these processes are nothing more than specific examples of highly controlled nucleation and growth phenomena such as those described in generic terms in Chapter 7. At a molecular level, these processes are controlled by the same reaction mechanisms involving oxide surfaces, which were outlined in Chapter 6. However, biomineralization is orders of magnitude more sophisticated than standard nucleation and growth processes. The unique features of biomineralization involve the interplay between organic biomolecules and the nucleation and growth of inorganic phases such as oxides. This interplay is of critical importance in both biology and emerging nanotechnologies, providing specific examples that illustrate many of the concepts of oxide chemistry introduced in Chapters 5 through 7. In this chapter, we highlight the key concepts of biomineralization and provide examples of how researchers can now produce complex nanostructured oxides via biomimetic nucleation and growth strategies that replicate some of the key features used to make hard tissues in living systems. These strategies include the use of (1) molecular complexation and compartmentalization to control supersaturation levels, (2) specific ligands and surface structures to mediate nucleation phenomena, (3) hierarchical self-assembled organic architectures as templates for oxide formation, (4) functionalization to stimulate desired heterogeneous nucleation and growth processes on those templates, and (5) organic surfactants to manipulate both crystal-phase preferences and growth habits.
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Croskerry, Pat. "A Hard Tale to Swallow." In The Cognitive Autopsy, edited by Pat Croskerry, 157–68. Oxford University Press, 2020. http://dx.doi.org/10.1093/med/9780190088743.003.0024.
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This case describes the experience of a young woman who spends 28 hours in an emergency department before her diagnosis is made. She endures numerous transitions of care between successive physicians that involve a variety of biases in an emergency department that is extremely busy at times. Personal characteristics of the patient appear to make her vulnerable to multiple implicit biases: race, obesity, psychiatric stigmatization, and others. A particular feature of the case is inattentional blindness, which surfaces in several other cases in this book.
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"Paddlefish Management, Propagation, and Conservation in the 21st Century." In Paddlefish Management, Propagation, and Conservation in the 21st Century, edited by CECIL A. JENNINGS and STEVEN J. ZIGLER. American Fisheries Society, 2009. http://dx.doi.org/10.47886/9781934874127.ch1.
Повний текст джерелаАнотація:
<em>Abstract</em>.—Paddlefish <em>Polyodon spathula </em>are among the largest and longest lived of the freshwater fishes (e.g., more than 2.2 m long; 72 kg; 30 years old) and can be distinguished by the presence of a large mouth and a long, paddle-shaped snout. Smooth skin, small eyes, a large, tapering operculum flap, bluish- gray to black coloration dorsally, and a deeply forked heterocercal caudal fin all serve to distinguish paddlefish from other species. Paddlefish become sexually mature and spawn at a later age than many other freshwater fishes; males mature at an earlier age than females, but maturity varies by latitude. Male paddlefish typically spawn each year, but spawning periodicity may be variable for females. Paddlefish spawn over gravel or other hard surfaces and require specific photoperiod, water temperature, and water flow for successful spawning. Paddlefish are relatively fecund (9,000–26,000 eggs per kilogram of body weight); mature eggs range from about 2.0–4.0 mm in diameter, and time from egg fertilization to hatching is directly related to water temperature. Optimum temperature for hatching is about 18_C. Newly hatched larvae average about 8.5 mm total length (TL) and are passive drifters until they are about 17 mm long when the yolk sac has been absorbed and the larvae begin active feeding on zooplankton and insects. Paddlefish complete fin ray development at 145–160 mm TL; at this size, they are considered juveniles and are similar in appearance to adults. Few paddlefish reach the maximum known age; instead, the median age for most populations is 5–8 years and maximum age is 14–18 years. Paddlefish growth seems to be directly related to the length of the growing season and food abundance. Generally, paddlefish length increases rapidly for about the first 5 years. After 5 years, paddlefish weight increases rapidly and may double during this time. Paddlefish feed primarily on zooplankton but occasionally consume small insects, insect larvae, and small fish. Traditionally, paddlefish inhabited slow-moving waters of side channels and river-lakes. In regulated rivers, paddlefish congregate where current velocities are reduced. In large rivers, paddlefish tend to congregate in the deep waters, usually selecting areas with depths greater than 3 m and current velocities less than 0.5 m/s. Further, paddlefish are highly mobile and make extensive movements within a system. Most of this movement is random, but paddlefish also make extensive nonrandom movements in spring during upstream migration to spawning areas. Some aspects of paddlefish life history and biology make them highly vulnerable to human activities. High prices for paddlefish roe or flesh periodically have stimulated fishing pressure and overexploitation followed by rapid declines in some populations. Dredging, flow manipulation, and the construction of dams have altered much of the traditional paddlefish habitat. Increasing levels of recreational and commercial boat traffic may also contribute to the mortality of paddlefish. Understanding and considering paddlefish biology and ecology can contribute to scientifically sound stewardship of all paddlefish populations, whether management is for conserving healthy populations or restoring decimated stocks.
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S., Kannan, and Anusuya S. "Detection of Tumor From Brain MRI Images Using Supervised and Unsupervised Methods." In AI Innovation in Medical Imaging Diagnostics, 61–75. IGI Global, 2021. http://dx.doi.org/10.4018/978-1-7998-3092-4.ch003.
Повний текст джерелаАнотація:
Brain tumor discovery and its segmentation from the magnetic resonance images (MRI) is a difficult task that has convoluted structures that make it hard to section the tumor with MR cerebrum images, different tissues, white issue, gray issue, and cerebrospinal liquid. A mechanized grouping for brain tumor location and division helps the patients for legitimate treatment. Additionally, the method improves the analysis and decreases the indicative time. In the separation of cerebrum tumor, MRI images would focus on the size, shape, area, and surface of MRI images. In this chapter, the authors have focused various supervised and unsupervised clustering techniques for identifying brain tumor and separating it using convolutional neural network (CNN), k-means clustering, fuzzy c-means grouping, and so on.
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Wayne, Marta L., and Benjamin M. Bolker. "4. HIV." In Infectious Disease: A Very Short Introduction, 41–53. Oxford University Press, 2015. http://dx.doi.org/10.1093/actrade/9780199688937.003.0004.
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HIV is the human immunodeficiency virus that causes acquired immunodeficiency syndrome, or AIDS. Its transmission is by exchange of bodily fluids. HIV can only enter immune cells with the surface protein gp120. The virus can hide in these cells for many years before it is activated, although it can be transmitted throughout this period. Once activated, the virus begins to replicate, ultimately causing the immune system of the infected person to collapse making them vulnerable to opportunistic infections. ‘HIV’ describes how evolutionary biology has been used to clarify the origins of the epidemic. The rapid mutation rates and recombination that make HIV very hard to treat are also explained. Despite these challenges, a regimen of highly active anti-retroviral therapies (HAART), developed in the mid 1990s, is extraordinarily effective against HIV.
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O'Brien, William. "Europe: The Birthplace of Mining?" In Prehistoric Copper Mining in Europe. Oxford University Press, 2014. http://dx.doi.org/10.1093/oso/9780199605651.003.0006.
Повний текст джерелаАнотація:
The origins of mining extend back several million years to when the first hominines in Africa, and subsequently in Europe and Asia, used their bare hands to collect loose rock to make stone tools. This gradually evolved into the systematic collection of rocks with desired properties, as well as an interest in earth minerals such as iron ochre. A desire for these substances led in some cases to more organized collection, involving surface quarrying and eventually underground mining. This activity increased significantly in Europe with the adoption of farming after 7000 BC in the Neolithic period. There is evidence for highly organized mining of flint and other hard rocks to make stone axes and other tools at centres such as Grimes Graves in England, Spiennes in Belgium, and Casa Montero near Madrid, among many others. Mining is also the process by which metal was obtained from the Earth’s surface. Metal objects were first made in the Middle East approximately 10,000 years ago; however, the oldest known copper mines are recorded in Europe. The discovery there of thousands of copper, bronze, and gold objects is a strong indicator that the mining of these metals was a widespread activity during the late prehistoric period. This began with the first use of copper and gold in what is known as the Chalcolithic (‘Copper Age’), which occurred in different regions between the sixth and third millennia BC. Technical advances and growing demand for metal led to the widespread adoption of bronze by 2000 BC, or soon afterwards. This was made possible by the discovery of copper and tin sources in many parts of Europe. Some of these were mined intensively over long periods during the Bronze Age that followed, while others were worked on a smaller scale. The copper produced was supplied to areas without their own resources, creating trade networks that provided economic opportunities and played an important role in cultural exchanges across the Continent. This book is concerned with the prehistory of copper mining and its important place in shaping European societies during the period 5500–500 BC.
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Zalasiewicz, Jan. "Gold!" In The Planet in a Pebble. Oxford University Press, 2010. http://dx.doi.org/10.1093/oso/9780199569700.003.0015.
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This is the beginning of the long goodbye to the surface realm. The flakes and grains of the pebble material are now in utter darkness (except perhaps for occasional flickers of phosphorescence from some of that microbial life), at the bottom of that deep, stagnant sea. The strata that we see in the pebble are a few centimetres thick. But now, of course, they are made of good, hard, respectable, tightly compressed rock. Back then, they made a layer of mud—waterlogged, sticky, slimy, and very likely evil-smelling mud—a quarter of a metre thick or more, that formed part of a layer on the sea floor that extended for tens of kilometres in every direction. Let us catch it at just this point in time, before it became buried by further influxes of sediment from those endless turbidity currents. The mud was full of life, particularly at the surface, most of which will have been occupied by those infinitely complex microscopic city-states that are microbial mats. But even below that, in the buried mud itself, there will have been considerable activity. In fact, as microbes are extremely good at clinging to life in all kinds of conditions, that activity was to carry on for quite some time yet. Those indefatigable microbes, though, still had to earn their keep. One way of doing that was by making use of the soft tissues of the fallen plankton, that were dismantled and recycled in the process that we call decay. Even in these anoxic conditions, where decay was slow, the magnificent, complex molecular architecture of body tissues was beginning to degrade, to transform into smaller, simpler molecules, leaving just the considerable inedible remnants that are the cases of the acritarchs and the chitinozoa, and the living quarters of the graptolites, upon which the microbes did not seem to manage to get much of a foothold (so to speak), even though they had decades and centuries in which to make the attempt. It is one thing to be occupied in this microscopic breaker’s yard, amid the wreckage of proteins, fats, and carbohydrates.
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Fox, Raymond. "Introduction." In The Use of Self. Oxford University Press, 2011. http://dx.doi.org/10.1093/oso/9780190616144.003.0006.
Повний текст джерелаАнотація:
While certainly a mystery, as Palmer suggests, a teacher’s mission, as well as reward, is educating, drawing out from students what lies dormant while proposing the new, the exhilarating, the as-yet undiscovered. Professors, especially those new to academe, frequently find themselves in the classroom with little preparation, guidance, or direction about how to convey the knowledge and skill set of the profession. The prevailing assumption is that advanced knowledge of subject matter itself is sufficient preparation to teach the subject. The unofficial credential for teaching is completion of a research doctorate in a particular discipline. This narrow position is reinforced by the belief that students will learn from a one-way transmission of information. Many of us have learned to teach the hard way, by the seat of our pants, by circumstance, or by necessity. We often teach unaware of how we teach, both at the surface level of recognizing and identifying what we do in the classroom, and at the philosophical level of considering why we do what we do. Theoretical frameworks and findings from research studies provide only limited assistance in mastering the art and craft of teaching. Between the ideas that research provides and the kinds of direction and decisions you, the teacher, must make, there is a gulf. Teachers, both new and experienced, seek practical yet innovative suggestions for creatively working with students. They need help with difficult questions. How do I divide my focus between establishing a relationship, developing a learning contract, and plunging into content? How can I enhance the learning process without actually getting in the way? How do I best connect with students? How can I make learning active? In what ways can I personalize the teaching/learning environment? How do I adapt the method of teaching to students’ differing learning styles? How do I keep content fresh for them and for me? How do I create a climate that is calming while challenging? How do I build a secure place to invite learning and change? Themes in this book resemble those in my other books that concentrate on clinical practice. They are heartfelt and basic.
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Brock, Fred V., and Scott J. Richardson. "Thermometry." In Meteorological Measurement Systems. Oxford University Press, 2001. http://dx.doi.org/10.1093/oso/9780195134513.003.0006.
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Air temperature is one of the most fundamental of all meteorological measurements and directly effects our everyday lives. It has been measured for centuries, using countless different techniques. One might assume that accurate air temperature measurements are readily made. Indeed, it is possible to make very accurate air temperature measurements but it can be a remarkably hard task, especially when limitations such as power consumption, reliability, and cost are involved. Errors in the measurement of air temperature in excess of 2 to 3°C are not uncommon in many networks. Errors of this magnitude are generally acceptable for the general public who is most interested in what clothes to wear for the day. However, numerical models at all scales of motion (mesoscale, synoptic scale, or climate models) are greatly affected by errors even as large as 1°C. Errors of just 1°C in a mesoscale model have been shown to be the deciding factor between no storms initiated and intense storms (Crook, 1996). In addition, errors as small as 0.2°C can change the prediction of a global climate model, depending on its dependency on initial conditions (DeFelice, 1998). Measurement of air temperature near the surface of the earth is facilitated by the vast array of temperature sensors and supporting electronic modules that are readily available. Accuracy is limited not by technology but by our ability to use it and by our ability to avoid exposure error, that is, to provide adequate coupling with the atmosphere. The preferred temperature scales are Celsius and Kelvin. These scales can be used almost interchangeably (except when absolute temperature is required) because a temperature difference of 1 K is equal to a temperature difference of 1°C. The Fahrenheit scale is still in general use by the U.S. public. Some common temperature reference points are shown in table 4-1. The triple point of water is the temperature and pressure where all three phases, gas, liquid, and solid, can coexist. Temperature sensors can be categorized according to the physical principle that they use: thermal expansion, thermoelectric, electrical resistance, electrical capacitance and some other effects.
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Lowenstam, Heinz A., and Stephen Weiner. "Protoctista." In On Biomineralization. Oxford University Press, 1989. http://dx.doi.org/10.1093/oso/9780195049770.003.0006.
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This kingdom is denned by exclusion, in that its members are neither animals, plants, fungi, nor prokaryotes. They comprise eukaryotic microorganisms and their immediate descendants (Margulis and Schwartz 1988). Of the 27 phyla that make up this kingdom, no less than 17 contain members that form mineralized hard parts. Although the vast majority of Protoctista are microorganisms, their smallness does not in any way imply an inability to control their biomineralization processes. On the contrary, many of the mineralizing Protoctista form very elaborate and complex structures. D’Arcy Thompson was one of many natural scientists who was both intrigued and fascinated by their skeletal morphologies. A perusal of his book On Growth and Form shows beautifully illustrated examples of protoctist skeletons and the text reveals a rare insight into some of the forces that govern their structure-forming processes. In the Radiolaria, for example, Thompson (1942) concludes that “the symmetry which the organism displays seems identical with that symmetry offerees which results from the play and interplay of surface- tensions in the whole system: this symmetry being displayed, in one class of cases, in a more or less spherical mass of froth, and in another class in a simpler aggregation of a few, otherwise isolated, vesicles” (p. 723). Although elegant and simple, physicochemical processes of interfacial chemistry are not sufficient to explain the complex, genetically controlled morphologies of many radiolarian species. Skeletal morphology is most likely the product of the delicate interplay between biologically controlled and physicochemically controlled processes (Anderson 1986). This is a recurring theme in biomineralization. Not all the protoctists are expert mineralizers. In fact they exhibit the whole spectrum of mineralization processes, from uncontrolled to finely tuned. Within the foraminifera and testate amoeba, among the Rhizopoda, are examples in which this wide diversity is found even within an individual phylum. They both contain species that construct their tests entirely out of organic materials or organic materials reinforced with mineral grains scavenged from the environment. They also contain species in which the test is mineralized by the organism itself, and at least in the case of the foraminifera, this can occur both intracellularly and extracellularly (Lowenstam 1986).
Тези доповідей конференцій з теми "Surfaces of hard-to-make"
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Pavel, Radu, Keith Sinram, Dana Combs, Jim Pillar, and Ioan Marinescu. "Surface Finish for a Case of Continuous and Interrupted OD Hard Turning." In ASME 2003 International Mechanical Engineering Congress and Exposition. ASMEDC, 2003. http://dx.doi.org/10.1115/imece2003-42538.
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Hard turning is the process to watch in many industries, as it is a perfect candidate for the actual trends toward automation and flexible manufacturing. However, there are still many possible conjunctures created by different geometries or materials of the workpieces versus different types of cutting tools with effect on workpiece surface quality, tool wear, machine tool vibrations, etc. These insufficiently explored combinations make manufacturers hesitate to adopt hard turning as a finishing process. This paper brings new findings concerning the effect of cutting parameters and tool nose radius variations on surface finish as a result of continuous and interrupted hard turning. The considered workpieces are a camshaft made of AISI 1117 steel at 62 HRC for continuous cutting, and a spline shaft made of AISI 1137 steel at 48 HRC for interrupted cutting. Two types of PcBN cutting tools are used for both types of component parts. The investigation highlights the differences between the ideal, geometrically determined, surface roughness Ra and the experimental results, as well as the differences recorded between the continuous and interrupted cutting situations. The factorial experimentation technique was employed taking the resulting surface rughness (Ra) as a response variable. The influence of tool wear was finally considered in the analysis of the predicted values of roughness obtained through characteristic regression equations. A significant difference of roughness evolution versus tool wear was recorded for the continuous and interrupted surfaces. The analysis was completed based on profilometry and light interferometry measurements as well as optical and SEM microscopy observations.
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Singh, Ramesh, Rick Kalil, Shreyes N. Melkote, and Fukuo Hashimoto. "Correlation of 3-D Precision Machined Surface Topography With Frictional Response." In ASME 2004 International Mechanical Engineering Congress and Exposition. ASMEDC, 2004. http://dx.doi.org/10.1115/imece2004-59534.
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Precision surface finishes are used in a wide variety of applications. From bearing races and rolling elements to parallel slide ways, the functional characteristics of these surfaces are critical to their performance. Experimental trial and error has shown that certain surfaces outperform others in certain applications, but the specific surface characteristics that make this true are yet to be fully understood. The present paper addresses this issue through a detailed three-dimensional topographic analysis of different precision finished surfaces and correlation with their frictional response. Experiments are conducted to investigate the effect of surface type (Isotropic Finished, Ground, Hard Turned and Honed) and relative surface speed on the coefficient of friction in rolling/sliding contact. Utilizing white light interferometry measurement of the surfaces, different 3-D topographic parameters such as RMS deviation, density of summits and texture direction are obtained and their correlation with the experimentally obtained coefficients of friction is examined. Results show that the 3-D amplitude parameter Sq (RMS deviation of surface) and spatial parameter Sds (density of summits) play an important role in determining the frictional behavior of the surfaces studied.
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Nonaka, Yuta, Mitsuyoshi Nomura, Tatsuya Fujii, Tsunehisa Suzuki, and Yongbo Wu. "Effects of Alpha-Cellulose Supply on the Working Life of MCF Slurry in MCF Polishing." In JSME 2020 Conference on Leading Edge Manufacturing/Materials and Processing. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/lemp2020-8568.
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Abstract High precision surfaces exhibit prominent capabilities for enhancing the imaging quality, expanding the visibility of equipment, simplifying structures, and reducing total costs of optical systems. Hence, they are regarded as essential optical surfaces for replacing traditional elements to modify optical systems, including space systems, optical inspection systems, and smart devices. Single point diamond turning (SPDT) and ultra-precision grinding have been adopted preliminarily to manufacture high-quality elements. However, these processes create sub-surface damage and tool marks on the work surface. To meet performance requirements, polishing is critical for post-processing to improve the quality of the products. MCF (Magnetic Compound Fluid) polishing, which is one of polishing methods using magnetic fields, is a processing method for finishing hard and brittle materials with high accuracy. Previous research has shown that MCF polishing is effective for hard and brittle materials. However, despite the high cost of the magnetic fluid that is a component of the MCF slurry, the MCF slurry used for polishing has been discarded. Another major issue was that unused MCF slurry could not be used due to drying. The purpose of this study is to recycle MCF slurry to solve this problem, and to develop high precision finishing technology. Therefore, in this study, a novel MCF polishing method using ultrasonic atomization is proposed, and the effects of α-cellulose on the MCF polishing are investigated. In addition, in order to make it possible to reuse the MCF slurry, In addition, experiments are conducted to enable reuse of MCF slurry.
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Tanaka, Tomohisa, Chikara Yamanaka, Keiji Kyogoku, and Tsunamitsu Nakahara. "The Effect of Interaction Between Neighboring Asperity Contacts on Wear Mode Transition in Sliding Contact of Rough Surfaces." In World Tribology Congress III. ASMEDC, 2005. http://dx.doi.org/10.1115/wtc2005-63617.
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Concerning the final aim, that is to make clear the mechanism of the wear mode transition from mild to severe belong to the increase of contact pressure in adhesive wear, estimation of the yielding condition in subsurface under contact boundary between rough surfaces was attempted in this study. Especially the effects of interaction between neighboring contacts as well as relative sliding on the yielding area were focused. The contacts between asperities were modeled by the contact between two neighboring hard wedges with the parallel axes and soft plane to be simplified. These models were calculated by commercial FEM solver in 2-dimension. Additionally, the effect of the difference between the heights of two wedges on the yielding region was evaluated by comparing the result with that obtained from the simple model of two wedges with the same height in non-sliding contact. The results showed that the effect of the interaction between adjacent contacts and existence of relative slip motion give significant factors to the yielding state, on the other hand, the height difference between neighboring asperities affects little the determination of the yielding region.
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Shemenski, Patrick D., and Brian P. Trease. "Compact Directional and Frictional Hinges for Flat Folding Applications." In ASME 2018 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/detc2018-86225.
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Thick-rigid deployable origami structures make use of compliant mechanisms to create folds and hinging surfaces. This paper examines the potential types of compact directional and frictional hinges to supplement the usage of compliant mechanisms in flat-folding applications. Rigid motioncontrolling hinges offer many opportunities to deployable origami. Hinges, in the form of hard stops, ratchets, or spring detents can allow for complex shape generation through kinematic manipulation. Hinged origami lends itself well to the creation of origami robotics, deployable structures, and arrays. With the ability to offer a high packing factor and create a self-supporting deployable structure, further research should be conducted into the application and development of hinged origami.
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Wei, Shizhong, Jinhua Zhu, Liujie Xu, and Rui Long. "The Study on Abrasive Wear of Carbon of High Vanadium High Speed Steel Compared With That of High Chromium Cast Iron." In World Tribology Congress III. ASMEDC, 2005. http://dx.doi.org/10.1115/wtc2005-63590.
Повний текст джерелаАнотація:
It is studied the carbons abrasive wear property of high vanadium high speed steel compared with that of general high chromium cast iron (Cr20) in this paper. The vanadium content is 10% in the high vanadium high speed steel, and it is a kind of new wear material that has been studied in the past ten years. In the experiment the three materials were used to resist the abrasive wear of Al2O3, the wear test was conducted on a ML-10 abrasive wear-testing machine. The abrasive surfaces, cross-section and sloping -section surfaces were scanned by means of a SEM (JSM-5160LV) device. The typical morphology photos of VC and Cr7C3 were taken in course of abrasive wear, which not only describe the different abrasive wear property of the carbons in the two materials, but also make the cause of the excellent wear property of this HSS clear. The research results have showed that the service lives (V10) are three times longer than that of high chromium cast iron (Cr20). The excellent wear resistance of high vanadium high-speed steel depends on the characters of high hardness, lumpy morphology of VC which are scattered in hard matrix of HSS.
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Gupta, Varan, Rohit Patel, Jitendra P. Khatait, and I. N. Kar. "Modelling of Continuous Contact-Based Skating Technique." In ASME 2018 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/detc2018-85598.
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Quick locomotion has always been a challenge for humanoid robots. Most of the work has been done to improve the efficiency of the walking gaits. Recently, additional equipment like skates are increasingly being used to speed up location, but they also make the system highly unstable. This paper describes the development of a statically stable skating gait to facilitate movement across plain surfaces, such as roads and hard ice. The new gait utilises the non-holonomic nature of a wheel (or blade of an ice skate). The proposed motion of the skates on the ground plane enables it to propel the robot forward without lifting its leg. Kinematic and dynamic equations of an equivalent model are formulated. Further, the paper discusses the relationship between different input signals and their corresponding output gaits. Multibody dynamics software is then used to simulate and verify the results for various scenarios. The design of an equivalent model with three degrees of freedom is then analysed and discussed for practical testing. Finally, the algorithm was tested on a fabricated robot.
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Song, Fengmei, and Andrew Nordquist. "A Large-Scale Model Developed for Predicting the Corroding Conditions of a Carrier Pipe in a Casing." In 2012 9th International Pipeline Conference. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/ipc2012-90475.
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The corroding conditions of a cased carrier pipe segment are difficult to measure in the field. It is hard to know whether or how well the cased pipe segment is cathodically protected. The pipeline industry needs a tool that can predict the in-situ corrosion potential of the carrier pipe in the casing annulus in order to determine the level of cathodic protection (CP). This work reports on a large-scale, three-dimensional computer model developed to make such a prediction. The casing wall may be treated as bare or coated on both or either of the external and internal surfaces. The carrier pipe is coated, and the coating quality inside the annulus may or may not be the same as the outside of the casing segment. The casing annulus is full of electrolytes. The model is used to investigate the effect of several factors on the level of CP imposed on the carrier pipe in the annulus, including the coating quality on the carrier pipe, the casing wall native potentials (both external and internal), the presence of a coating on a casing wall surface, and a metallic contact (between the casing and the carrier pipe) with the contact resistance being a variable. The effect of the voltage variation inside the pipe metal wall is also investigated.
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Nakatsuka, Matthew, Basile Marco, Sumil Thapa, Alexander Ventura, Osvaldo Pascolini, Luca Pellicciotta, and Vinod Veedu. "Decarbonization and Improved Energy Efficiency Using a Novel Nanocomposite Surface Treatment." In Abu Dhabi International Petroleum Exhibition & Conference. SPE, 2021. http://dx.doi.org/10.2118/208080-ms.
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Abstract Fouling of heat exchanger equipment through the formation and attachment of hard scale, microbially induced corrosion (MIC) products, or particulate erosion is a serious challenge to reliable production in the oil and gas industry. Exchangers which become fouled in this way perform 15-30% worse than their rated ability, requiring either constant intervention to clean away biofilms, continuous injection of biocides and corrosion inhibitors, or the regular plugging of tubes to prevent leaks, representing a significant operating expense and billions of dollars in lost production time. When an exchanger is unable to provide sufficient heat due to tube fouling, additional sources of heating must be utilized to make up for this deficit and to ensure that facility processes remain within design allowances. This need for supplemental heating is a significant source of carbon emissions in the industry and represents a significant obstacle towards decarbonization efforts. However, it also represents an economically attractive way to simultaneously lower emissions while also lowering a producer's cost per barrel. This work describes an alternate strategy to control and prevent fouling in heat exchangers, through the one-time application of an omniphobic (water- and oil-repelling) nano-surface treatment. Once applied to a heat exchanger, the extremely smooth and low-surface energy material greatly reduces the ability of MIC-causing bacteria to deposit and adhere to the surface. Because it imparts functionality to the surface itself, rather than simply function as a physical barrier, it enables long lasting protection which was validated under laboratory conditions in a pressurized autoclave, as well as two pilot demonstrations. Results from both the laboratory and field evaluations of the treatment's promise showed that treated surfaces showed a corrosion rate over 36-times lower when compared to untreated surfaces, while also completely arresting the formation of corrosion pitting, tube fouling, and erosion of the tube interior. These field-validated results were then applied to the observed heating deficit of a proposed deployment site, resulting in calculated carbon emissions savings of up to 17,000 Tons CO2 per year.
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Nakatsuka, Matthew Allan, Bryan K. Ghahremani, Phuong Dinh, Sumil Singh Thapa, Alexander Donovan Ventura, and Vinod Veedu. "Rapid Decarbonization Through Maximizing Gains from Process Improvements." In Offshore Technology Conference. OTC, 2022. http://dx.doi.org/10.4043/32123-ms.
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Abstract One of the biggest points of emphasis for the energy production industry is how to effectively decarbonize and reduce the footprint of generation activities while still maintaining sufficient capacity to fulfill the energy needs of the world at large. Unlike many other sectors that can pivot to alternate forms of zero-emission fuel, the very nature of fossil fuel extraction, production, and transmission makes this transition particularly difficult and expensive. Small, immediate gains in efficiency with minimal investment can play a significant role in both smoothing the energy transition as well as extending the window where climate effects and increases in global temperatures above 3.5°F can still be mitigated or eliminated. Previous work and field trials presented by the authors have demonstrated that efficiency losses associated with fouling of heat transfer surfaces are a significant contributor to carbon emissions; in steam generation plants, fouling of the main condenser can lead to increased backpressure and reductions in power output. Hard deposit buildup on the pre-heat train (PHT) of a refinery can result in dramatically increased fuel use to raise the temperature of production fluid so that is ready for separation and distillation. New materials capable of imparting low-surface energy properties and greatly reduced surface roughness have been demonstrated to significantly decrease fouling in many of these cases, opening untapped operational capacity. However, without careful monitoring of the exchanger itself, this capacity may go entirely unrealized and un-utilized. This paper presents a new strategy in developing a monitoring and prescriptive maintenance solution that can specifically work as a complement to determine improved heat transfer performance after refurbishment by an anti-fouling surface treatment. The thermal sensor intelligence module (TSIM) was designed to be a lightweight and self-contained system, with the ability to be easily deployed on heat transfer equipment. To make accurate and precise predictions for the absence or presence of fouling on a treated system, where both historical and real-time data may be limited, an ensemble learning method was utilized in conjunction with a subscale condenser system whereby the TSIM could be rapidly trained on a variety of simulated fouling conditions, and the presence or absence of treatment. The learning method demonstrated in this work allowed for the TSIM to improve its fouling predictions through a model that allows it to impute the values of different parameters if the deployed exchanger or condenser does not have the necessary instrumentation. This imputation and prediction of the missing exchanger parameters allows for the accuracy be improved by nearly 20%, and the precision and F1 scores to be comparable to the model with a full set of input features. Finally, results gathered from this test condenser system, and the calculation of heat transfer efficiency showed good correlation with previously reported field data gathered under similar conditions, with a roughly 3-7% improvement after the addition of the anti-fouling treatment.