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Flexure
Kinds of Flexure Selected AbstractsNanoclay-reinforced syntactic foams: Flexure and thermal behaviorPOLYMER COMPOSITES, Issue 8 2010Mrinal C. Saha Syntactic foams containing 60 vol% of hollow glass microballoons in epoxy matrix are modified with untreated nanoclays using combined mechanical and ultrasonication methods. Effects of nanoclays on flexure and thermal behavior of syntactic foams are investigated by adding different amount of nanoclays in the range of 1,3% by weight. Microscopic examinations and physical property characterization are performed to determine the interactions among constituent materials and the void formation during fabrication. It is found that the syntactic foams with 2 wt% nanoclays show the highest improvement in flexural properties (,42% strength and ,18% modulus) and dynamic mechanical properties (,30% storage modulus and ,28% loss modulus) properties. Thermal decomposition temperature is found to be unaffected by the addition of nanoclays, whereas a continuous reduction in the coefficient of thermal expansion (CTE) is observed. An examination of failure surface indicates that the failure is initiated on the tension side of the flexure sample due to fracturing of microballoons. POLYM. COMPOS., 31:1332,1342, 2010. © 2009 Society of Plastics Engineers [source] Ductility of Reinforced Concrete Flat Slab-Column ConnectionsCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 3 2005Maria Anna Polak Post peak-load ductility of connections in reinforced concrete framed structures is essential for ensuring structural integrity and preventing local failure that may lead to progressive collapse of such systems. The importance of ductility for resistance against abnormal loading and the role of transverse reinforcement in providing ductility is discussed, and a new shear-strengthening technique, shear bolts, is presented. Shear bolts are a special type of reinforcement developed specially for retrofitting of existing, previously built, flat slabs. The results of an experimental work are presented which show how transverse reinforcement increases punching shear capacity and post-failure ductility of slab-column connections. The described work also applies a specially developed finite element formulation based on layered shell elements, to the analysis of continuous reinforced concrete slabs. The formulation is applicable for global structural analysis of slabs failing in flexure or punching modes. The finite element and experimental results are compared in the article. [source] A fibre flexure,shear model for seismic analysis of RC-framed structuresEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 5 2009P. Ceresa Abstract While currently existing modelling approaches of reinforced concrete (RC) behaviour allow a reasonably accurate prediction of flexural response, the determination of its shear counterpart needs further developments. There are various modelling strategies in the literature able to predict the shear response and the shear,flexure coupling under monotonic loading conditions. However, very few are the reported models that have demonstrated successful results under cyclic loading, as in the seismic load case. These considerations lead to this research work focused on the development of a flexure,shear model for RC beam,column elements. A reliable constitutive model for cracked RC subjected to cyclic loading was implemented as bi-axial fibre constitutive model into a two-dimensional Timoshenko beam,column element. Aim of this research work is to arrive at the definition of a numerical model sufficiently accurate and, at the same time, computationally efficient, which will enable implementation within a finite element package for nonlinear dynamic analysis of existing non-seismically designed RC structures that are prone to shear-induced damage and collapse. Copyright © 2009 John Wiley & Sons, Ltd. [source] A displacement-based seismic design procedure for RC buildings and comparison with EC8EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 10 2001T. B. Panagiotakos Abstract A procedure for displacement-based seismic design (DBD) of reinforced concrete buildings is described and applied to a 4-storey test structure. The essential elements of the design procedure are: (a) proportioning of members for gravity loads; (b) estimation of peak inelastic member deformation demands in the so-designed structure due to the design (,life-safety') earthquake; (c) revision of reinforcement and final detailing of members to meet these inelastic deformation demands; (d) capacity design of members and joints in shear. Additional but non-essential steps between (a) and (b) are: (i) proportioning of members for the ULS against lateral loads, such as wind or a serviceability (,immediate occupancy') earthquake; and (ii) capacity design of columns in flexure at joints. Inelastic deformation demands in step (b) are estimated from an elastic analysis using secant-to-yield member stiffnesses. Empirical expressions for the deformation capacity of RC elements are used for the final proportioning of elements to meet the inelastic deformation demands. The procedure is applied to one side of a 4-storey test structure that includes a coupled wall and a two-bay frame. The other side is designed and detailed according to Eurocode 8. Major differences result in the reinforcement of the two sides, with significant savings on the DBD-side. Pre-test calculations show no major difference in the seismic performance of the two sides of the test structure. Copyright © 2001 John Wiley & Sons, Ltd. [source] Thermal Shock Damage of a 3D-SiC/SiC Composite,ADVANCED ENGINEERING MATERIALS, Issue 11 2005S. Wu Thermal shock of a three-dimensional (3D) SiC/SiC composite prepared by chemical vapor infiltration (CVI) process was conducted using water quenched method. Thermal shock damage of the composite was assessed by SEM characterization and measurement mechanical properties using three-point flexure after quenching. After quenched from 1200°C to 25°C water for 100 cycles, the composite retained 80% of the original flexural strength in the longitudinal direction while cracked through the width direction. Thermal shock damage of the composite was analyzed by thermal stress analysis based on the braiding structure of the composite as well as the distribution and shape of flaws referred to residual pores in the matrix. The braided structure and the dimension difference resulted in the anisotropy of mechanical properties and the matrix pores configuration of the composite, which led to the thermal shock damage anisotropy of the composite. [source] Development of colonic stenosis following severe acute pancreatitisHPB, Issue 3 2003F Maisonnette Background Colonic necrosis after acute pancreatitis is rare. When it does occur, it is commonly due to ischaemia or inflammation and may necessitate early colonic resection. Case outline A 72-year-old man developed colonic necrosis 6 weeks after severe acute pancreatitis. CT scan revealed a bulky mass near the left colon. Barium enema and colonoscopy revealed stenosis of the left colonic flexure, and this segment of bowel was successfully resected. Discussion Severe acute pancreatitis must be recognised as a cause of colonic ischaemia and necrosis. The possible pathogenic mechanisms include severe local inflammation and an ischaemic process. This complication is associated with a very poor prognosis despite surgical intervention, but a timely resection may prevent further problems. [source] Incidence and Prognosis of Colorectal Dysplasia in Inflammatory Bowel Disease: A Population-based Study from Olmsted County, Minnesota,INFLAMMATORY BOWEL DISEASES, Issue 8 2006Tine Jess MD Abstract Background and Aims: The risk, fate, and ideal management of colorectal dysplasia in inflammatory bowel disease (IBD) remain debated. We estimated the incidence, long-term outcome, and risk factors for progression of colorectal dysplasia (adenomas [adenoma-associated lesions or masses (ALMs)], flat dysplasia, and dysplasia-associated lesions or masses [DALMs]) in a population-based IBD cohort from Olmsted County, Minnesota. Materials and Methods: The Rochester Epidemiology Project was used to identify cohort patients with colorectal dysplasia. Medical records were reviewed for demographic and clinical characteristics. Histology slides were reviewed by a pathologist blinded to previous pathology reports. The cumulative incidence of dysplasia was estimated, and the association between patient characteristics and recurrence/progression of dysplasia was assessed using proportional hazards regression. Results: Twenty-nine (4%) IBD patients developed flat dysplasia (n = 8), DALMs (n = 1), ALMs in areas of IBD (n = 18), or ALMs outside areas of IBD (n = 2). Among 6 patients with flat low-grade dysplasia (fLGD) who did not undergo colectomy, none progressed during a median of 17.8 (range 6,21) years of observation with a median of 3 (range 0,12) surveillance colonoscopies. Four (22%) patients with ALMs in areas of IBD who did not undergo surgery developed LGD or DALMs. Primary sclerosing cholangitis and dysplasia located proximal to the splenic flexure were significantly associated with risk for recurrence/progression of dysplasia. Conclusions: This population-based cohort study from Olmsted County, Minnesota did not confirm an increased risk of cancer related to fLGD, whereas 22% of patients with ALMs in areas of IBD developed fLGD or DALMs. [source] Bending of fluid-saturated linear poroelastic beams with compressible constituentsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 4 2009Zhi-Hua Wang Abstract Analytical solutions are presented for fluid-saturated linear poroelastic beams under pure bending. The stress-free boundary condition at the lateral surfaces is satisfied in the St Venant's sense and the Beltrami,Michell compatibility conditions are resolved rigorously, rendering the flexure of the beams analytically tractable. Two sets of formulations are derived based on the coupled and uncoupled diffusion equations respectively. The analytical solutions are compared with three-dimensional finite element simulations. Both sets of analytical formulations are capable of capturing exactly both the initial (undrained) and the steady-state (fully drained) deflection of the beams. However, the analytical solutions are found to be deficient during the transient phase. The cause for the deficiency of the transient analytical solutions is discussed. The accuracy of the analytical solutions improves as Poisson's ratio and the compressibility of the constituents of the porous beam increase, where the St Venant's edge effect at the lateral surfaces is mitigated. Copyright © 2008 John Wiley & Sons, Ltd. [source] Size Scaling of Tensile Failure Stress in a Float Soda,Lime,Silicate GlassINTERNATIONAL JOURNAL OF APPLIED GLASS SCIENCE, Issue 2 2010Andrew A. Wereszczak The (tensile) strength,size scaling of a float soda,lime,silicate glass was studied using biaxial flexure and Hertzian ring crack initiation testing. The examined Weibull effective areas spanned ,0.4,48,000 mm2. Both the air and tin sides were tested. The air side was stronger than the tin side as others have observed; however, the differences in their characteristic strengths decreased with a decreasing effective area, and their strengths converged for effective areas smaller than ,100 mm2. The failure stress at the smallest effective area examined for the tin side was ,500% greater than that at the largest effective area, while that difference was ,250% for the air side. A Weibull modulus change at ,100 mm2 suggests different strength-limiting flaw types were dominant below and above this effective area. These results reinforce the importance of the interpretation and use of the tensile strength of glass in context to how much of its area is being subjected to tensile stress. [source] The changing incidence and sites of colorectal cancer in the Israeli Arab population and their clinical implicationsINTERNATIONAL JOURNAL OF CANCER, Issue 1 2007Paul Rozen Abstract Israeli Arabs have been at low risk for colorectal cancer (CRC) and had mainly proximal cancer, but increasing CRC is now noted. We examined this trend and CRC site and compared them to the total Jewish population and to the low-risk Jews of Asian-African origin. Israel Cancer Registry CRC data, 1982,2002, for Arabs and Jews was computed by gender, age and site: rectal cancer included recto-sigmoid junction; "right-sided" CRC included the proximal colon up to and also the splenic flexure. During 1982,2002, Arab CRC trends increased significantly in both sexes due to left -sided CRC (women, p = 0.01; men, p = 0.02) and rectal cancers (p = 0.05). Left -sided CRC increased significantly in both men and women aged , 65 years (p = 0.02). Comparing 1982,1984 to 2000,2002, the proportion of right-sided CRC decreased in both genders (p < 0.01) from 39.4 to 27.1% of male CRC, and from 44.8 to 31.3% in females. In general, this pattern of increasing rectal and left-sided CRC had been seen over a decade earlier in Jews of Asian-African origin and then their trend reversed during the last decade. In conclusion, there is a recent trend for left-sided CRC in Israeli Arabs, probably related to their changing life style. These results should influence their cancer preventive lifestyle recommendations, and CRC screening and diagnostic methodologies used. © 2006 Wiley-Liss, Inc. [source] Theoretical investigation of elastic flexural properties for multistranded orthodontic archwiresJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 3 2002Brian K. Rucker Abstract The bending and torsional stresses during flexure were detailed and simplified for a single twisted strand, which emulates a spring. General expressions were derived to evaluate the elastic properties (i.e., strength, stiffness, and range) of multistranded wires by combining the effects of a number of outer twisted strands, with or without an inner strand. Specific expressions were solved for single-stranded, twisted, and coaxial wires. Initially, we considered the following multistranded wire configurations: two- (twin), three- (triple), four-strand (quad) twisted, and coaxial wires. The elastic properties of the twin and quad wires were essentially subsets of the triple wire. For a given overall wire diameter (D) and helix angle (,), the ranges of multistranded wires were independent of wire configurations. By varying the , from 45 to 85°, the D from 0.394 to 0.546 mm (15.5 to 21.5 mil), and the stress at the proportional limit from 1.03 to 3.28 GPa (150 to 475 ksi), the theoretical elastic properties of triple and coaxial stainless steel wires matched many of the properties of conventional nickel titanium leveling wires. © 2002 Wiley Periodicals, Inc. J Biomed Mater Res 62: 338,349, 2002 [source] Ceramometal Bonded Inlays and OnlaysJOURNAL OF ESTHETIC AND RESTORATIVE DENTISTRY, Issue 3 2000HARRY F. ALBERS DDS ABSTRACT Porcelain-fused-to-metal (PFM) is presently the most popular crown and bridge technique. Its success is attributable to the use of a metal substructure to support the porcelain, resulting in good esthetics, limited ceramic flexure, and better longevity than all-porcelain restorations. A new concept suggests encapsulating the metal substructure with ceramic and placing the insert under the occlusal surface, thereby combining the best properties of the esthetics of porcelain and the support of metal to achieve improved restorations. CLINICAL SIGNIFICANCE The ceramometal bonded restoration (CMBR) addresses the known limitations of PFMs by providing a more esthetic, more conservative, and more durable alternative. The CMBR eliminates the potential for tooth darkening, leaves more of the natural tooth intact, and offers good resistance to fracture or displacement under occlusal forces. This combination of features makes the CMBR inlay or onlay an excellent alternative for the conservative esthetic restoration of posterior teeth. [source] CLINICAL CHARACTERISTICS and PROGNOSIS OF COLORECTAL SIGNET-RING CELL CARCINOMAJOURNAL OF GASTROENTEROLOGY AND HEPATOLOGY, Issue 2001Kook Lae Lee Background/aims, Colorectal signet-ring cell carcinoma (SRCC) is uncommon tumor. The aim of this study was to evaluate the clinical characteristics of primary and metastatic colorectal SRCC. Methods, We retrospectively examined the records of patients who had undergone surgery for colon cancer and was diagnosed pathologically as colorectal SRCC from 1988 to 2000. Results, Among 1812 patients with colorectal cancer examined, the number of patients with SRCC was 28 (1.5%); eight patients (28.6%) were metastatic and 20 patients (71.4%) were primary. Male to female ratio was 19:9 and mean age was 44.2 (primary, 42.5; metastatic, 48.3). Mean age of primary SRCC of rectosigmoid area was lower than that of ascending colon (37.4 vs. 54.5). The topographic incidences of primary SRCC were nine patients in rectum; five patients in sigmoid colon; six patients in ascending colon. Metastatic SRCC's were mostly found in splenic flexure and rectosigmoid area. Biopsy positive rate at first was 13 of 18 in primary SRCC, and 3 of 5 in metastatic SRCC. Five cases (55.6%) of primary rectal SRCC showed linitis plastica type. The stage of primary SRCC showed a preponderance of Astler,Coller C2 lesions; 3 (15%) were in B2, 1 (5%) was in C1, 14 (70%) were in C2, 2 (10%) were in D. One and two years survival of primary SRCC were 62.7 and 45.7%, respectively. Conclusions, Colorectal SRCC is rare among colon cancer and common in young age group especially which is primary or occurs in rectosigmoid area. The primary SRCC's were mostly found in advanced stage, and the prognosis might be poor. [source] DETERMINATION OF FAULT SLIP COMPONENTS USING SUBSURFACE STRUCTURAL CONTOURS: METHODS AND EXAMPLESJOURNAL OF PETROLEUM GEOLOGY, Issue 3 2004S-S. Xu Problems with measuring fault slip in the subsurface can sometimes be overcome by using subsurface structural contour maps constructed from well logs and seismic information. These maps are useful for estimating fault slip since fault motion commonly causes the dislocation of structural contours. The dislocation of a contour is defined here as the distance in the direction of fault strike between two contours which have the same value on both sides of a fault. This dislocation can be estimated for tilted beds and folded beds as follows: (i),If a dip-slip fault offsets a tilted bed, the dislocation (Sc) of contours can be estimated from the vertical component (Sv) of the fault slip and the dip (,) of the bedding according to the following relationship: Sc= Sv/tan ,. Since Sc and , can be measured from a contour map, the vertical component of fault slip can be obtained from this equation. If a strike-slip fault offsets a tilted bed, the dislocation (Scs) of contours is equal to the strike-slip of the fault (Sc), that is, Scs= Ss. (ii),If a fault offsets a symmetric fold, the strike component (Scs) of fault slip and the dislocation of the contours (Sc) can be calculated, respectively, from the equations Scs= (Smax+ Smin) / 2 and Sc= (Smax - Smin) / 2. Smax is the greater total dislocation (Sc+ Scs) of a contour line between the two limbs of the fold and Smin is the smaller total dislocation (Sc - Scs) for the same contour line. In this case, Sv can be also calculated using the obtained value of Sc and the equation Sv= Sc tan ,. Similarly, for an asymmetric fold, the dislocation of contours due to the vertical slip component is Scb= (Smax - Smin)/(n + 1), and the strike-slip component is Ss= Scs= (nSmin+ Smax/(n + 1), where n is the ratio between the values of interlines of the two limbs, and Scb is the dislocation of contours due to the vertical slip component for either of the two limbs (here it is for limb b). In all cases, three conditions are required for the calculation of contour dislocation: (i),the contour lines must be approximately perpendicular to the fault strike; the intersection angle between the fault strike and the strike of bedding should be greater than 65°; (ii),the bed must not be dip more than 35°; and (iii),folding or flexure of the stratigraphic horizons must have occurred before faulting. These methods for determining fault slip from the dislocation of structural contours are discussed using case studies from the Cantarell oilfield complex, Campeche Sound (southern Gulf of Mexico), the Jordan-Penwell Ellenburger oilfield in Texas, and the Wilmington oilfield in California. [source] Biaxial Flexural Strength and Microstructure Changes of Two Recycled Pressable Glass CeramicsJOURNAL OF PROSTHODONTICS, Issue 3 2004Mohammad Albakry BSc Purpose: This study evaluated the biaxial flexural strength and identified the crystalline phases and the microstructural features of pressed and repressed materials of the glass ceramics, Empress 1 and Empress 2. Materials and Methods: Twenty pressed and 20 repressed disc specimens measuring 14 mm × 1 mm per material were prepared following the manufacturers' recommendations. Biaxial flexure (piston on 3-ball method) was used to assess strength. X-ray diffraction was performed to identify the crystalline phases, and a scanning electron microscope was used to disclose microstructural features. Results: Biaxial flexural strength, for the pressed and repressed specimens, respectively, were E1 [148 (SD 18) and 149 (SD 35)] and E2 [340 (SD 40), 325 (SD 60)] MPa. There was no significant difference in strength between the pressed and the repressed groups of either material, Empress 1 and Empress 2 (p > 0.05). Weibull modulus values results were E1: (8, 4.7) and E2: (9, 5.8) for the same groups, respectively. X-ray diffraction revealed that leucite was the main crystalline phase for Empress 1 groups, and lithium disilicate for Empress 2 groups. No further peaks were observed in the X-ray diffraction patterns of either material after repressing. Dispersed leucite crystals and cracks within the leucite crystals and glass matrix were features observed in Empress 1 for pressed and repressed samples. Similar microstructure features,dense lithium disilicate crystals within a glass matrix,were observed in Empress 2 pressed and repressed materials. However, the repressed material showed larger lithium disilicate crystals than the singly pressed material. Conclusions: Second pressing had no significant effect on the biaxial flexural strength of Empress 1 or Empress 2; however, higher strength variations among the repressed samples of the materials may indicate less reliability of these materials after second pressing. [source] Design and performance of an ultra-high-vacuum-compatible artificial channel-cut monochromatorJOURNAL OF SYNCHROTRON RADIATION, Issue 1 2008Suresh Narayanan The design and performance of a novel ultra-high-vacuum-compatible artificial channel-cut monochromator that has been commissioned at undulator beamline 8-ID-I at the Advanced Photon Source are presented. Details of the mechanical and optical design, control system implementation and performance of the new device are given. The monochromator was designed to meet the challenging stability and optical requirements of the X-ray photon correlation spectroscopy program hosted at this beamline. In particular, the device incorporates a novel in-vacuum sine-bar drive mechanism for the combined pitch motion of the two crystals and a flexure-based high-stiffness weak-link mechanism for fine-tuning the pitch and roll of the second crystal relative to the first crystal. The monochromator delivers an exceptionally uniform and stable beam and thereby improved brilliance preservation. [source] Glass Strengthening Via High-Intensity Plasma-Arc HeatingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2010Andrew A. Wereszczak A high-intensity plasma-arc lamp was used to irradiate the surface of soda,lime silicate glass tiles to determine whether an increase in strength could be achieved. The lamp has a maximum power density of 3500 W/cm2, a processing area of 2 cm × 10 cm, a broad-spectrum energy distribution between 0.2 and 1.4 ,m, and was controlled to unidirectionally sweep across 50 mm2 tiles at a constant speed of 8 mm/s. Ring-on-ring (RoR) equibiaxial flexure and four-point unidirectional flexure testings of entire tiles were used to measure and compare uncensored and unimodal Weibull failure stress distributions of treated and untreated glass. Even under nonoptimized processing conditions, the RoR Weibull characteristic failure stress increased by approximately 25% and the four-point-bend Weibull characteristic failure stress increased by approximately 65%. Additionally, the failure stresses of the weakest samples of the heat-treated glass were significantly higher than those of the untreated glass. Strengthening was due to a fire-polishing-like mechanism. The arc-lamp heat treatment caused the location of the strength-limiting flaws in the four-point-bend tiles to change; namely, failure initiation occurred on the gauge section surface for the treated glass, whereas it occurred at a gauge section edge for the untreated glass. Arc-lamp heat treatment is attractive not only because it provides strengthening, but because it can (noncontact) process large amounts of glass quickly and inexpensively, and is a process that either a glass manufacturer or an end-user can readily use. [source] Mechanical Properties of Monoclinic ZirconiaJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2004Jens Eichler Fracture toughness and fracture strength data are presented for the first time for monoclinic zirconia. An undoped nanocrystalline zirconia powder was sintered at 1100°C and yielded a theoretical density of more than 90% with a grain size of about 150 nm. The surface crack in flexure (SCF) technique was deemed most suitable for nanocrystalline materials. Measurements of Young's modulus and the determination of the fracture origin are also provided. [source] Comparison of Methods to Determine the Fracture Toughness of Three Glass-Ceramics at Elevated TemperaturesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2000Janet B. Quinn Two standardized methods for measuring kIc in ceramics are compared for use at high temperatures (precracked beam and surface crack in flexure). Results from a third technique involving the measurement of cracks around Vickers indentations are also presented. Three dental glass-ceramics, differing primarily in microstructure, were used as model materials in this study. They emphasized the importance of microstructure in determining high-temperature kIc values and the challenges in measuring them. The measured fracture toughnesses decreased with temperature and increased with imbedded grain size for all three methods. [source] Controlling and Testing the Fracture Strength of Silicon on the MesoscaleJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2000Kuo-Shen Chen Strength characterizations and supporting analysis of mesoscale biaxial flexure and radiused hub flexure single-crystal silicon specimens are presented. The Weibull reference strengths of planar biaxial flexure specimens were found to lie in the range 1.2 to 4.6 GPa. The local strength at stress concentrations was obtained by testing radiused hub flexure specimens. For the case of deep reactive ion-etched specimens the strength at fillet radii was found to be significantly lower than that measured on planar specimens. This result prompted the introduction of an additional isotropic etch after the deep reactive ion etch step to recover the strength in such regions. The mechanical test results reported herein have important implications for the development of highly stressed microfabricated structures. The sensitivity of the mechanical strength to etching technique must be accounted for in the structural design cycle, particularly with regard to the selection of fabrication processes. The scatter of data measured in the mechanical tests clearly illustrated the need to use a probabilistic design approach. Weibull statistics may be the appropriate means to describe the data, although a simple two-parameter Weibull model only provides a moderately good fit to the experimental data reported in this study. [source] Oxytocin stimulates colonic motor activity in healthy womenNEUROGASTROENTEROLOGY & MOTILITY, Issue 2 2004B. Ohlsson Abstract, The effects of oxytocin in the gastrointestinal tract are unclear. The aim of this study was to examine the effect of infusion of oxytocin on colonic motility and sensitivity in healthy women. Fourteen healthy women were investigated twice. A 6-channel perfusion catheter, with three recording points (2 cm apart) proximally and three recording points distally to a barostat balloon, was inserted to the splenic flexure. An intestinal feeding tube was placed in the mid-duodenum. A 90-min duodenal lipid infusion of 3 kcal min,1 was administered. Thirty minutes after the start of the lipid infusion, the subject randomly received either 20 or 40 mU min,1 of oxytocin, or isotonic saline as intravenous infusions for 90 min. Meanwhile, the colonic motility was recorded. During the last 30 min of oxytocin and saline infusion, the visceral sensitivity to balloon distensions was examined. During lipid infusion the number of antegrade contractions per hour was 0.7 ± 0.3 after saline and 3.9 ± 1.4 after oxytocin (P = 0.03), indicating more pronounced lumen-occlusive contractile activity after oxytocin administration. Some of these consisted of high-amplitude (> 103 mmHg in amplitude) antegrade contractions. Lipid infusion evoked a decrease of the balloon volume, reflecting increased colonic tone, but there was no difference between saline and oxytocin. Sensory thresholds did not differ significantly between saline and oxytocin. Infusion of oxytocin stimulates antegrade peristaltic contractions in stimulated colon in healthy women. The effects of oxytocin on colonic motor activity deserve to be further explored, especially in patients with colonic peristaltic dysfunction. [source] Nanoclay-reinforced syntactic foams: Flexure and thermal behaviorPOLYMER COMPOSITES, Issue 8 2010Mrinal C. Saha Syntactic foams containing 60 vol% of hollow glass microballoons in epoxy matrix are modified with untreated nanoclays using combined mechanical and ultrasonication methods. Effects of nanoclays on flexure and thermal behavior of syntactic foams are investigated by adding different amount of nanoclays in the range of 1,3% by weight. Microscopic examinations and physical property characterization are performed to determine the interactions among constituent materials and the void formation during fabrication. It is found that the syntactic foams with 2 wt% nanoclays show the highest improvement in flexural properties (,42% strength and ,18% modulus) and dynamic mechanical properties (,30% storage modulus and ,28% loss modulus) properties. Thermal decomposition temperature is found to be unaffected by the addition of nanoclays, whereas a continuous reduction in the coefficient of thermal expansion (CTE) is observed. An examination of failure surface indicates that the failure is initiated on the tension side of the flexure sample due to fracturing of microballoons. POLYM. COMPOS., 31:1332,1342, 2010. © 2009 Society of Plastics Engineers [source] New Insight on the Anatomy and Architecture of the Avian NeurocraniumTHE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 3 2009Jesús Marugán-Lobón Abstract This study aims to disentangle the main features of the avian neurocranium at high taxonomic scales using geometric morphometric tools. When surveying the variation across 60% of avian orders (sampled among 72 individuals), our results verify that the central nervous system has an important influence upon the architecture of the avian neurocranium, as in other very encephalized vertebrates such as mammals. When the avian brain expands relative to the cranial base it causes more "reptilian-like" neurocranial configurations to shape into rounder ones. This rounder appearance is achieved because the cranial base becomes relatively shorter and turns its flexure from concave to convex, at the same time forcing the foramen magnum to reorient ventrally instead of caudally. However, our analyses have also revealed that an important morphological difference between birds resides between the occiput and the cranial roof. This variation was unexpected since it had not been reported thus far, and entertains two plausible interpretations. Although it could be due to a trade-off between the relative sizes of the supraoccipital and the parietal bones, the presence of an additional bone (the intra- or post-parietal) between the latter two bones could also explain the variation congruently. This descriptive insight stresses the need for further developmental studies focused in understanding the evolutionary disparity of the avian neurocranium. Anat Rec, 292:364,370, 2009. © 2009 Wiley-Liss, Inc. [source] Gross Anatomy of the Intestine in the Giraffe (Giraffa camelopardalis)ANATOMIA, HISTOLOGIA, EMBRYOLOGIA, Issue 6 2009W. Pérez Summary We describe the macroscopic anatomy of the intestine of the giraffe (Giraffa camelopardalis). The small intestine was divided into duodenum, jejunum and ileum as usual. The caecum was attached to the ileum by a long ileocaecal fold, and to the proximal ansa of the ascending colon by a caecocolic fold. The ascending colon was the most developed portion of the gross intestine and had the most complex arrangement with three ansae: the proximal ansa, the spiral ansa and the distal ansa. The proximal ansa completely encircled the caecum, describing a 360° gyrus, and represented the widest portion of the intestine. The spiral ansa was formed by three and a half centripetal gyri, a central flexure and three centrifugal gyri. The last centrifugal gyrus left the spiral and described nine flexures of different form and direction over the left side of the mesentery. The two portions that formed each of these flexures ran parallel to each other. The last part of this gyrus ran parallel to the jejunum. When compared with domestic cattle, giraffe had a comparatively short small intestine and a comparatively long large intestine, with a resulting small ratio of small:large intestine. Reasons are presented why this should be considered a peculiarity of cattle-like ruminants rather than a different representative of a browser,grazer dichotomy in general. [source] Observations on the Macroscopic Anatomy of the Intestinal Tract and its Mesenteric Folds in the Pampas Deer (Ozotoceros bezoarticus, Linnaeus 1758)ANATOMIA, HISTOLOGIA, EMBRYOLOGIA, Issue 4 2008W. Pérez Summary We described the macroscopic anatomy of the intestines and their peritoneal folds of five adult pampas deer (Ozotoceros bezoarticus), a cervid species considered to ingest a high proportion of grass in its natural diet. The mean (±SD) body weight was 17 (±2) kg. The small intestine and the caecocolon measured 495 (±37) cm and 237 (±24) cm in length, respectively, with an average ratio (small intestine:caecocolon) of 1.9 (±0.1). The ascending colon had two and a half centripetal gyri, a central flexure and two centrifugal gyri. The spiral ansa, which was similar to an ellipse, was fixed to the whole left face of the mesenterium. Apart from the peritoneal folds described in the Nomina Anatomica Veterinaria, three additional, hitherto not described folds were found: a fold that fixed the caecum to the proximal ansa of the ascending colon, one that joined the terminal part of the proximal ansa to the last centrifugal gyrus of the spiral ansa of the ascending colon, and one that linked the ascending duodenum to the proximal ansa of the ascending colon. When compared with published data from other cervids of different feeding niches, it appears that, among cervids, the ratio of small intestine to the caecocolon length does not reflect the natural diet. [source] An Overview of Complete Artificial Fixed Dentition Supported by Endosseous ImplantsARTIFICIAL ORGANS, Issue 1 2005Dennis Flanagan Abstract:, The construction of a complete restoration of the dentition by the surgical placement of endosseous titanium implants that support a fixed prosthesis in each jaw is possible. The positionings of the implants and teeth in the prostheses are important factors for a successful long-term result. Distribution of the occlusal biting forces over as many implants as possible is important. Off-axial occlusal biting forces should be diverted to the anterior jaws where the forces are not as great. The posterior teeth should be designed with flat occlusal surfaces that separate during excursionary mandibular chewing movements. Medial mandibular flexure caused by the contraction of the medial pterygoid muscle can be addressed by constructing the prosthesis in segments, so as not to have a rigid entity encased in flexing bone that may induce stress in the bone, potentially leading to loss of implant integration and failure. Segmenting also ensures an appropriate fit of the prosthesis with respect to casting and porcelain firing distortion. Lip support by means of a flange in the prosthesis may be necessary when there has been a large amount of bone loss from edentulous resorption. Cleaning and routine maintenance of the prostheses every 3,6 months is essential. [source] High-speed serial-kinematic SPM scanner: design and drive considerations,ASIAN JOURNAL OF CONTROL, Issue 2 2009Kam K. Leang Abstract This paper describes the design of a flexure-guided, two-axis nanopositioner (scanner) driven by piezoelectric stack actuators. The scanner is specifically designed for high-speed scanning probe microscopy (SPM) applications, such as atomic force microscopy (AFM). A high-speed AFM scanner is an essential component for acquiring high-resolution, three-dimensional, time-lapse images of fast processes such as the rapid movement of cells and the diffusion of DNA molecules. A two-axis SPM scanner is proposed, where the slow and fast scanning axes are serially connected and flexure guided to minimize runout. The scanner's achievable scan range is approximately 10µm × 10µm. Finite element analysis is utilized to optimize the mechanical resonance frequencies of the scanner. Experimental results show a first major resonance in the slow and fast axis at 1.5 and 29,kHz, respectively. This paper also discusses the various tradeoffs between speed, range, electrical requirements, and scan trajectory design for high-speed nanopositioning. Copyright © 2009 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source] Abfraction: separating fact from fictionAUSTRALIAN DENTAL JOURNAL, Issue 1 2009JA Michael Abstract Non-carious cervical lesions involve loss of hard tissue and, in some instances, restorative material at the cervical third of the crown and subjacent root surface, through processes unrelated to caries. These non-carious processes may include abrasion, corrosion and possibly abfraction, acting alone or in combination. Abfraction is thought to take place when excessive cyclic, non-axial tooth loading leads to cusp flexure and stress concentration in the vulnerable cervical region of teeth. Such stress is then believed to directly or indirectly contribute to the loss of cervical tooth substance. This article critically reviews the literature for and against the concept of abfraction. Although there is theoretical evidence in support of abfraction, predominantly from finite element analysis studies, caution is advised when interpreting results of these studies because of their limitations. In fact, there is only a small amount of experimental evidence for abfraction. Clinical studies have shown associations between abfraction lesions, bruxism and occlusal factors, such as premature contacts and wear facets, but these investigations do not confirm causal relationships. Importantly, abfraction lesions have not been reported in pre-contemporary populations. It is important that oral health professionals understand that abfraction is still a theoretical concept, as it is not backed up by appropriate clinical evidence. It is recommended that destructive, irreversible treatments aimed at treating so-called abfraction lesions, such as occlusal adjustment, be avoided. [source] Differential compaction due to the irregular topology of a diagenetic reaction boundary: a new mechanism for the formation of polygonal faultsBASIN RESEARCH, Issue 3 2009R. J. Davies ABSTRACT We propose a new mechanism for the formation of some polygonal fault arrays. Seismically imaged opal-A (biogenic silica) to opal-CT (cristobalite and tridymite) diagenetic boundaries from two regions offshore of Norway have developed regular wavelength patterns. The pattern consists of cell-shaped elevations that are 200,2600 m wide and up to 200 m high, separated by troughs. The cells represent regions that undergo diagenesis at shallower burial depths, earlier than adjacent areas. The chemical change leads to mechanical compaction and porosity reduction; therefore subsidence occurs above the cells in the overburden. Roughly circular depressions form above the cells, and a network of folds form above inter-cell areas. Networks of normal faults form on the crests and margins of the folds as a result of flexure during the folding. The progressive lateral growth of the cells causes the depressions to widen and intervening folds to narrow resulting in new differential compaction-induced faults to form with variable strike orientations. Lateral and vertical growth of cells leads to cells conjoining and the re-establishment of a uniform planar reaction boundary. This novel but simple mechanism can explain some polygonal fault arrays that form above opal-A to opal-CT reaction boundaries and in these settings the mechanism should be considered in addition to syneresis, density inversion or low coefficients of residual friction which are the most commonly cited drivers for polygonal fault systems. [source] Sedimentation record in the Konkan,Kerala Basin: implications for the evolution of the Western Ghats and the Western Indian passive marginBASIN RESEARCH, Issue 1 2008D. Campanile ABSTRACT The Konkan and Kerala Basins constitute a major depocentre for sediment from the onshore hinterland of Western India and as such provide a valuable record of the timing and magnitude of Cenozoic denudation along the continental margin. This paper presents an analysis of sedimentation in the Konkan,Kerala Basin, coupled with a mass balance study, and numerical modelling of flexural responses to onshore denudational unloading and offshore sediment loading in order to test competing conceptual models for the development of high-elevation passive margins. The Konkan,Kerala Basin contains an estimated 109 000 km3 of Cenozoic clastic sediment, a volume difficult to reconcile with the denudation of a downwarped rift flank onshore, and more consistent with denudation of an elevated rift flank. We infer from modelling of the isostatic response of the lithosphere to sediment loading offshore and denudation onshore infer that flexure is an important component in the development of the Western Indian Margin. There is evidence for two major pulses in sedimentation: an early phase in the Palaeocene, and a second beginning in the Pliocene. The Palaeocene increase in sedimentation can be interpreted in terms of a denudational response to the rifting between India and the Seychelles, whereas the mechanism responsible for the Pliocene pulse is more enigmatic. [source] | ||||||||||||||||||||||||||||||||||||||||