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Fiber Orientation (fiber + orientation)
Selected AbstractsMicroanatomy of the Mandibular Symphysis in Lizards: Patterns in Fiber Orientation and Meckel's Cartilage and Their Significance in Cranial EvolutionTHE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 8 2010Casey M. Holliday Abstract Although the mandibular symphysis is a functionally and evolutionarily important feature of the vertebrate skull, little is known about the soft-tissue morphology of the joint in squamate reptiles. Lizards evolved a diversity of skull shapes and feeding behaviors, thus it is expected that the morphology of the symphysis will correspond with functional patterns. Here, we present new histological data illustrating the morphology of the joint in a number of taxa including iguanians, geckos, scincomorphs, lacertoids, and anguimorphs. The symphyses of all taxa exhibit dorsal and ventral fibrous portions of the joints that possess an array of parallel and woven collagen fibers. The middle and ventral portions of the joints are complemented by contributions of Meckel's cartilage. Kinetic taxa have more loosely built symphyses with large domains of parallel-oriented fibers whereas hard biting and akinetic taxa have symphyses primarily composed of dense, woven fibers. Whereas most taxa maintain unfused Meckel's cartilages, iguanians, and geckos independently evolved fused Meckel's cartilages; however, the joint's morphologies suggest different developmental mechanisms. Fused Meckel's cartilages may be associated with the apomorphic lingual behaviors exhibited by iguanians (tongue translation) and geckos (drinking). These morphological data shed new light on the functional, developmental, and evolutionary patterns displayed by the heads of lizards. Anat Rec 293:1350,1359, 2010. © 2010 Wiley-Liss, Inc. [source] Partial unilateral absence of the trapezius muscle in a human cadaverCLINICAL ANATOMY, Issue 5 2001Jason G. Emsley Abstract We report here the partial unilateral absence of the trapezius muscle found during dissection. The left trapezius was significantly reduced in size when compared to the right trapezius, especially in its inferior third. Moreover, the existing fibers of the left trapezius inferior to the scapula were only one-third to two-thirds as thick as those on the right. The vertebral attachment of the inferior fibers of the left trapezius was also notably higher than that on the right. Morphometric analysis indicated that the surface area of the left trapezius was approximately 50% that of the right trapezius. Fiber orientation along the left and right trapezius muscles was also markedly different. An examination of nerve supply yielded no apparent anomalies, therefore suggesting that the absence of trapezius has a developmental etiology. Clin. Anat. 5:383,386, 2001. © 2001 Wiley-Liss, Inc. [source] Physical foundations, models, and methods of diffusion magnetic resonance imaging of the brain: A reviewCONCEPTS IN MAGNETIC RESONANCE, Issue 5 2007Ludovico Minati Abstract The foundations and characteristics of models and methods used in diffusion magnetic resonance imaging, with particular reference to in vivo brain imaging, are reviewed. The first section introduces Fick's laws, propagators, and the relationship between tissue microstructure and the statistical properties of diffusion of water molecules. The second section introduces the diffusion-weighted signal in terms of diffusion of magnetization (Bloch,Torrey equation) and of spin-bearing particles (cumulant expansion). The third section is dedicated to the rank-2 tensor model, the bb -matrix, and the derivation of indexes of anisotropy and shape. The fourth section introduces diffusion in multiple compartments: Gaussian mixture models, relationship between fiber layout, displacement probability and diffusivity, and effect of the b -value. The fifth section is devoted to higher-order generalizations of the tensor model: singular value decompositions (SVD), representation of angular diffusivity patterns and derivation of generalized anisotropy (GA) and scaled entropy (SE), and modeling of non-Gaussian diffusion by means of series expansion of Fick's laws. The sixth section covers spherical harmonic decomposition (SHD) and determination of fiber orientation by means of spherical deconvolution. The seventh section presents the Fourier relationship between signal and displacement probability (Q -space imaging, QSI, or diffusion-spectrum imaging, DSI), and reconstruction of orientation-distribution functions (ODF) by means of the Funk,Radon transform (Q -ball imaging, QBI). © 2007 Wiley Periodicals, Inc. Concepts Magn Reson Part A 30A: 278,307, 2007. [source] Mechanical behavior of bovine periodontal ligament under tension-compression cyclic displacementsEUROPEAN JOURNAL OF ORAL SCIENCES, Issue 1 2006Tatsuya Shibata In the present study, the mechanical response of bovine periodontal ligament (PDL) subjected to displacement-controlled tension,compression harmonic oscillations and subsequent rupture was examined. Specimens including dentine, cementum, PDL, and alveolar bone were extracted from different depths and locations of bovine first molars. They were immersed in a saline solution at room temperature and clamped on their bone and dentine extremities. The samples were tested at ±35% of the PDL's width, with a frequency of 1 Hz. The mechanical parameters evaluated were hysteresis, phase lag, and the modulus of the stress,stretch ratio curves in tension and compression. The tensile strength and the corresponding stretch ratio were also recorded. Stress,stretch ratio curves indicated a non-linear, time-dependent response with hysteresis and preconditioning effects. The hysteresis and phase lag in compression were much higher than in tension, suggesting that the dissipated energy was higher in compression than in tension. The root depth and location did not play essential roles for the tension or compression data, with the exception of limited statistical differences for tensile strength and corresponding stretch ratio. Thus, biological variability in the specimens, as a result of different bone contours, PDL width, and fiber orientation, did not affect the energy-absorbing capacity of the PDL. The evolution of the stress rate with stress demonstrated a constant increase of stiffness with stress. The stiffness values were twofold higher in tension than in compression. The data also showed that the stiffness of the PDL was comparable with data reported for other soft tissues. [source] Acrylonitrile,butadiene rubber/reclaimed rubber,nylon fiber compositeADVANCES IN POLYMER TECHNOLOGY, Issue 4 2001T. D. Sreeja The effect of diphenylmethane diisocyanate (MDI),polyethyleneglycol (PEG) resin on the cure characteristics and mechanical properties of nitrile rubber/whole tyre reclaim,short nylon fiber composite,was studied. At a constant loading of 5 phr, the resin composition was varied. The minimum torque and (maximum , minimum) torque increased with isocyanate concentration. Scorch time and cure time showed a reduction on introduction of bonding agent. Properties like tensile strength, tear strength, and abrasion resistance increased with increase in MDI/PEG ratio, and these properties are higher in the longitudinal direction of fiber orientation. Compression set increased with isocyanate concentration and the resilience remain unchanged. © 2001 John Wiley & Sons, Inc. Adv Polym Techn 20: 281,288, 2001 [source] Preparation of rubber composites from ground tire rubber reinforced with waste-tire fiber through mechanical millingJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2007Xin-Xing Zhang Abstract Composites made from ground tire rubber (GTR) and waste fiber produced in tire reclamation were prepared by mechanical milling. The effects of the fiber content, pan milling, and fiber orientation on the mechanical properties of the composites were investigated. The results showed that the stress-induced mechanochemical devulcanization of waste rubber and the reinforcement of devulcanized waste rubber with waste-tire fibers could be achieved through comilling. For a comilled system, the tensile strength and elongation at break of revulcanized GTR/fiber composites reached maximum values of 9.6 MPa and 215.9%, respectively, with 5 wt % fiber. Compared with those of a composite prepared in a conventional mixing manner, the mechanical properties were greatly improved by comilling. Oxygen-containing groups on the surface of GTR particles, which were produced during pan milling, increased interfacial interactions between GTR and waste fibers. The fiber-filled composites showed anisotropy in the stress,strain properties because of preferential orientation of the short fibers along the roll-milling direction (longitudinal), and the adhesion between the fiber and rubber matrix was improved by the comilling of the fiber with waste rubber. The proposed process provides an economical and ecologically sound method for tire-rubber recycling. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 4087,4094, 2007 [source] Lack of Effect of Conduction Direction on Action Potential Durations in Anisotropic Ventricular Strips of Pig HeartJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 4 2002GUILLERMO BERTRAN B.Sc. Anisotropy and Repolarization.Introduction: The influence of activation sequence on the rate of rise of the depolarization phase of action potentials in atrial or ventricular muscles has been well established. However, whether myocardial fiber orientation is important in modulating the repolarization process is unclear. Methods and Results: We examined the influence of activation sequence on the repolarization phase of action potentials in epicardial tissues from the right and left ventricles of domestic pigs. Whereas cells from the right ventricle exhibited direction-dependent differences in action potential duration at 30%, 50%, and 90% of full repolarization (190.6 ± 31.1 msec vs 181.8 ± 32.8 msec, 240.3 ± 23.5 msec vs 236.7 ± 25.4 msec, and 291.3 ± 23.7 msec vs 287.4 ± 25.1 msec for longitudinal and transverse propagation, respectively; P < 0.001), a similar duration of repolarization during both directions of propagation was observed in cells from the left ventricle at 50% and 90% of full repolarization (241.4 ± 39.4 msec and 285.5 ± 39.5 msec vs 240.4 ± 38.9 msec and 284.9 ± 39.6 msec for longitudinal and transverse propagation respectively; P = NS). A slight but significant difference was found at 30% of full repolarization in cells from the left ventricle (190.4 ± 39.0 msec vs 187.0 ± 38.0 msec for longitudinal and transverse propagation, respectively; P < 0.05). In the left ventricle, the duration of repolarization did not change as the distance between the recording site and stimulation site increased. Conclusion: The direction of wavefront propagation with respect to fiber orientation may not play an important role in modulating the duration of repolarization in epicardial cells from the left ventricle. [source] Reentry in a Morphologically Realistic Atrial ModelJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 9 2001EDWARD J. VIGMOND Ph.D. Reentry in Morphologically Realistic Atria.Introduction: Atrial fibrillation is the most common cardiac arrhythmia. In ablation procedures, identification of the reentrant pathways is vital. This has proven difficult because of the complex morphology of the atria. The purpose of this study was to ascertain the role of specific anatomic structures on reentry induction and maintenance. Method and Results: A computationally efficient, morphologically realistic, computer model of the atria was developed that incorporates its major structural features, including discrete electrical connections between the right and left atria, physiologic fiber orientation in three dimensions, muscle structures representing the crista terminalis (CT) and pectinate muscles, and openings for the veins and AV valves. Reentries were induced near the venous openings in the left and right atria, the mouth of the coronary sinus, and the free wall of the right atrium. The roles of certain muscular structures were ascertained by selectively removing the structures and observing how the propagation of activity was affected. Conclusion: (1) The muscular sheath of the coronary sinus acts as a pathway for a reentrant circuit and stabilizes any circuits that utilize the isthmus near the inferior vena cava. (2) Poor trans-CT coupling serves to stabilize flutter circuits. (3) Wall thickness is an important factor in the propagation of electrical activity, especially in the left atrium. (4) The openings of the inferior and superior venae cavae form natural anatomic anchors that make reentry easier to initiate by allowing for smaller ectopic beats to induce reentry. [source] Relating Instrumental Texture, Determined by Variable-Blade and Allo-Kramer Shear Attachments, to Sensory Analysis of Rainbow Trout, Oncorhynchus mykiss, FilletsJOURNAL OF FOOD SCIENCE, Issue 7 2010Aunchalee Aussanasuwannakul Abstract:, Texture is one of the most important quality attributes of fish fillets, and accurate assessment of variation in this attribute, as affected by storage and handling, is critical in providing consistent quality product. Trout fillets received 4 treatments: 3-d refrigeration (R3), 7-d refrigeration (R7), 3-d refrigeration followed by 30-d frozen storage (R3F30), and 7-d refrigeration followed by 30-d frozen storage (R7F30). Instrumental texture of raw and cooked fillets was determined by 3 approaches: 5-blade Allo-Kramer (AK) and variable-blade (VB) attachment with 12 blades arranged in perpendicular (PER) and parallel (PAR) orientations to muscle fibers. Correlation between instrumental texture and sensory hardness, juiciness, elasticity, fatness, and coarseness was determined. Muscle pH remained constant at 6.54 to 6.64. Raw fillets lost 3.66% of their original weight after 30-d frozen storage. After cooking, weight loss further increased to 15.97%. Moisture content decreased from 69.11 to 65.02%, while fat content remained constant at 10.41%. VBPER detected differences in muscle sample strength (P= 0.0019) and demonstrated effect of shear direction reported as maximum force (g force/g sample). AKPER detected differences in energy of shear (g × mm; P= 0.0001). Fillets that received F30 treatments were less extensible. Cooking increased muscle strength and toughness. Force determined by VBPER was correlated with sensory hardness (r= 0.423, P= 0.0394) and cook loss (r= 0.412, P= 0.0450). VB attachment is accurate, valid, and less destructive in fillet texture analysis. Practical Application:, A new shearing device was validated with sensory analysis. Settings and parameters obtained could be used to define fillet texture quality associated with muscle fiber orientation. [source] Effect of Temperature (,5 to 130 °C) and Fiber Direction on the Dielectric Properties of Beef Semitendinosus at Radio Frequency and Microwave FrequenciesJOURNAL OF FOOD SCIENCE, Issue 6 2008N. Basaran-Akgul ABSTRACT:, The dielectric properties must be defined to design efficient radio frequency (RF) and microwave (MW) processes by the food manufacturers. The objective of this study was to understand how frequency, temperature, and muscle fiber orientation influence the dielectric properties. The eye of round (Semitendinosus) muscle was selected because it contains large, relatively uniform muscle cells with similar muscle fiber orientation and relatively uniform chemical composition throughout the tissue. Dielectric properties were measured using an open-ended coaxial probe technique at 27, 915, and 1800 MHz and temperatures between ,5 and 130 °C. Power penetration depth was calculated. Since many commercially prepared, thermally processed, ready-to-eat entrees are made with frozen meat, dielectric property measurements were started from ,5 °C. The dielectric constant and dielectric loss factors were often higher for muscle with the muscle fiber measured in a parallel orientation to the probe compared to samples of the same treatment (for example, fresh or frozen) in a perpendicular tissue orientation at the same frequency and temperature. Dielectric constant and loss values for frozen beef tended to be higher than fresh beef at the same temperature and frequency. Tissue orientation appeared to have a greater effect on dielectric loss values at lower frequencies. Penetration depth tended to be greater when the direction of propagation was perpendicular to the muscle fiber. [source] Microneurography of human median nerveJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 6 2005Mehmet Bilgen PhD Abstract Purpose To examine the possibility of performing high-resolution MRI (microneurography) on peripheral nerves. Materials and Methods A specific radio frequency (RF) coil was developed to probe the human median nerve at a magnetic field strength of 9.4 T and tested on three excised samples by acquiring microneurograms. Results The microneurograms revealed neuronal tissue constituents at subfascicular level. The contrast features on proton-density and T1- and T2-weighted images were described and compared. The microscopic water movement was quantified using diffusion weighting parallel and orthogonal to the neuronal fiber orientation. The characteristics of anisotropic diffusion in the median nerve were comparable to those reported from other biological tissues (white matter and kidney). Conclusion The results overall suggest that microneurography might provide new noninvasive insights into microscopic gross anatomy of the peripheral nerve, injury evaluation, and efficacy of repair, although the feasibility at current clinically relevant field strengths is yet to be determined. J. Magn. Reson. Imaging 2005;21:826,830. © 2005 Wiley-Liss, Inc. [source] RHEOLOGICAL PROPERTIES OF MOZZARELLA CHEESE DETERMINED BY CREEP/RECOVERY TESTS: EFFECT OF SAMPLING DIRECTION, TEST TEMPERATURE AND RIPENING TIMEJOURNAL OF TEXTURE STUDIES, Issue 3 2009MARÍA LAURA OLIVARES ABSTRACT The viscoelastic properties of mozzarella cheese using a creep/recovery test considering different sampling directions (parallel and perpendicular to protein fiber orientation), test temperatures (20, 30 and 40C) and ripening times (1, 8, 15, 29 and 36 days) were studied. Creep data were interpreted by a Burger model of four parameters. A semiempirical approach was proposed to obtain the contribution of each main compliance to the total deformation of the system. Creep tests at different temperatures allowed gaining a better understanding of changes that occur in the cheese matrix during heating and ripening. Sampling direction did not affect any of the parameters studied. Finally, it was clearly observed that cheese matrix behaves as a quite different physicochemical system depending on temperature. Therefore, it is recommended to carry out the rheological tests at different temperatures to evaluate appropriately the viscoelastic properties of mozzarella cheese. PRACTICAL APPLICATIONS Mozzarella cheese must have certain characteristics to be used on pizzas and on other prepared foods that use the cheese in melted state. The protein chains in the mozzarella curds coalesce into large strands that are oriented in the direction of stretching. For this reason, mozzarella cheese has an anisotropic structure. Therefore, it is relevant to determine the effect of protein fiber orientation on the rheological properties. Valuable information may be obtained through the creep/recovery test of mozzarella cheese samples to study its rheological properties and to explain molecular mechanisms that occur during ripening or melting processes considering sampling direction. [source] Nondestructive optical determination of fiber organization in intact myocardial wallMICROSCOPY RESEARCH AND TECHNIQUE, Issue 7 2008Rebecca M. Smith Abstract Mapping the myocardial fiber organization is important for assessing the electrical and mechanical properties of normal and diseased hearts. Current methods to determine the fiber organization have several limitations: histological sectioning mechanically distorts the tissue and is labor-intensive, while diffusion tensor imaging has low spatial resolution and requires expensive MRI scanners. Here, we utilized optical clearing, a fluorescent dye, and confocal microscopy to create three-dimensional reconstructions of the myocardial fiber organization of guinea pig and mouse hearts. We have optimized the staining and clearing procedure to allow for the nondestructive imaging of whole hearts with a thickness up to 3.5 mm. Myocardial fibers could clearly be identified at all depths in all preparations. We determined the change of fiber orientation across strips of guinea pig left ventricular wall. Our study confirms the qualitative result that there is a steady counterclockwise fiber rotation across the ventricular wall. Quantitatively, we found a total fiber rotation of 105.7 ± 14.9° (mean ± standard error of the mean); this value lies within the range reported by previous studies. These results show that optical clearing, in combination with a fluorescent dye and confocal microscopy, is a practical and accurate method for determining myocardial fiber organization. Microsc. Res. Tech., 2008. © 2008 Wiley-Liss, Inc. [source] Polarized light imaging of white matter architectureMICROSCOPY RESEARCH AND TECHNIQUE, Issue 10 2007Luiza Larsen Abstract Polarized light imaging (PLI) is a method to image fiber orientation in gross histological brain sections based on the birefringent properties of the myelin sheaths. The method uses the transmission of polarized light to quantitatively estimate the fiber orientation and inclination angles at every point of the imaged section. Multiple sections can be assembled into a 3D volume, from which the 3D extent of fiber tracts can be extracted. This article describes the physical principles of PLI and describes two major applications of the method: the imaging of white matter orientation of the rat brain and the generation of fiber orientation maps of the human brain in white and gray matter. The strengths and weaknesses of the method are set out. Microsc. Res. Tech., 2007. © 2007 Wiley-Liss, Inc. [source] Role of proton MR for the study of muscle lipid metabolism,NMR IN BIOMEDICINE, Issue 7 2006Chris Boesch Abstract 1H-MR spectroscopy (MRS) of intramyocellular lipids (IMCL) became particularly important when it was recognized that IMCL levels are related to insulin sensitivity. While this relation is rather complex and depends on the training status of the subjects, various other influences such as exercise and diet also influence IMCL concentrations. This may open insight into many metabolic interactions; however, it also requires careful planning of studies in order to control all these confounding influences. This review summarizes various historical, methodological, and practical aspects of 1H-MR spectroscopy (MRS) of muscular lipids. That includes a differentiation of bulk magnetic susceptibility effects and residual dipolar coupling that can both be observed in MRS of skeletal muscle, yet affecting different metabolites in a specific way. Fitting of the intra- (IMCL) and extramyocellular (EMCL) signals with complex line shapes and the transformation into absolute concentrations is discussed. Since the determination of IMCL in muscle groups with oblique fiber orientation or in obese subjects is still difficult, potential improvement with high-resolution spectroscopic imaging or at higher field strength is considered. Fat selective imaging is presented as a possible alternative to MRS and the potential of multinuclear MRS is discussed. 1H-MRS of muscle lipids allows non-invasive and repeated studies of muscle metabolism that lead to highly relevant findings in clinics and patho-physiology. Copyright © 2006 John Wiley & Sons, Ltd. [source] Three-dimensional fiber orientation in vibration welded joints of glass fiber reinforced polyamide-6POLYMER COMPOSITES, Issue 9 2008Musa R. Kamal A technique was developed to obtain the three-dimensional distribution of fiber orientation in vibration-welded joints of polyamide-6 (PA-6) reinforced with 30 wt% glass fibers. The heat-affected zone (HAZ) of fiber-reinforced PA-6 was successfully revealed by polishing and etching the vibration welded joints. Examination with the polarized light microscope in the reflection mode showed detailed microstructure domains, including the bulk crystalline zone and the HAZ. Experimental elliptical fiber cross-section images were used to obtain second order orientation tensors, thus providing a quantitative description of the three-dimensional fiber orientation distribution. The fibers in the HAZ were reoriented towards the squeeze flow direction, when compared with the bulk phase. Low welding pressure does not necessarily produce a more favorable fiber orientation in the tensile direction than high welding pressure. High welding pressure and low amplitude promote fiber reorientation in both the squeeze flow and tensile (weld thickness) directions. Overall, it was found that, at 30% fiber content, vibration-welded joints of injection molded fiber-reinforced PA-6 are weaker than vibration-welded joints in unreinforced injection molded samples. The fibers in the former do not undergo sufficient reorientation to influence weld strength in the tensile direction. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers [source] Influence of fiber orientation on high stress wear behavior of sisal fiber-reinforced epoxy compositesPOLYMER COMPOSITES, Issue 4 2007Navin Chand Sisal fiber-reinforced epoxy composites having three different fiber orientations, namely LL, LT, TT mentioned in the text were prepared and tested for their high stress abrasive wear behavior. Effect of fiber orientation, sliding distance, and load on abrasive wear of sisal,epoxy composites have been determined. Wear data of composites have been compared with the pure epoxy. Incorporation of fibers decreases the wear rate of epoxy resin, which varies with the fiber orientation. Wear rate in case of TT composite is found minimum as compared to other two composites. Wear rate follows the following trend, WTT < WLT < WLL. Owing to minimum exposed area of fiber to the sliding asperities, lowest wear rate occurs in the case of TT composite. Increase of load and sliding distance increases the wear volume in all the composites, because of the progressive loss of material. Wear mechanism has been discussed by using SEM micrographs of the worn surfaces. POLYM. COMPOS., 28:437,441, 2007. © 2007 Society of Plastics Engineers. [source] Fiber orientation control of short-fiber reinforced thermoplastics by ram extrusionPOLYMER COMPOSITES, Issue 5 2003Yukio Sanomura In this study we examine the fiber orientation distribution, fiber length and Young's modulus of extruded short-fiber reinforced thermoplastics such as polypropylene. Axial orientation distributions are presented to illustrate the influence of extrusion ratio on the orientation state of the fibrous phase. Fibers are markedly aligned parallel to the extrusion direction with increasing extrusion ratio. The orientation state of extruded fiber-reinforced thermoplastics (FRTP) is almost uniform throughout the section. The control of fiber orientation can be easily achieved by means of ram extrusion. Experimental results are also presented for Young's modulus of extruded FRTP in the extrusion direction. Young's modulus follows a linear trend with increasing extrusion ratio because the degree of the molecular orientation and the fiber orientation increases. The model proposed by Cox, and Fukuda and Kawada describes the effect of fiber length and orientation on Young's modulus. The value of the orientation coefficient is calculated by assuming a rectangular orientation distribution and calculating the fiber distribution limit angle given by orientation parameters. By comparing the predicted Young's modulus with experimental results, the validity of the model is elucidated. The mean fiber length linearly decreases with increasing extrusion ratio because of fiber breakage due to plastic deformation. There is a small effect on Young's modulus due to fiber breakage by ram extrusion. [source] Short fibers suspension in steady recirculating flowsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2002Francisco Chinesta Abstract Numerical modeling of short fiber suspensions flows involves the coupling between motion equations, which definean elliptic problem, and the fluid constitutive equation, which introduces a non-linear advection problem related to the fiber orientation (induced anisotropy). In a previous work these authors have proposed a numerical procedure to determine a steady solution of the fibers orientation in steady recirculating flows, taking into account that neither initial nor boundary conditions are given. This procedure may be used in the numerical simulation of SFRT flows involving recirculating parts as encountered in the simulationof industrial processes, as well as in inverse rheological identification using, for example, rotative rheometric devices. La modélisation numérique des suspensions de fibres courtes implique le couplage entre les équations de mouvement (qui définissent un problème élliptique) et l'equation constitutive qui introduit un problème de transport non linéaire asocié à l'orientation des fibres. Les auteurs ont proposé, dans des travaux précédents, une technique numérique pour le calcul de l'orientation des fibres dans un écoulement stationnaire recirculant pour lequel les conditions aux limites et les conditions initiates ne sont pas connues. Cette technique peut être utilisée dans la simulation d'écoulements de fibres courtes présentant des recirculations, comme c'est le cas dans les écoulements industrielles en contraction ainsi que dans les instruments rhéométriques rotatifs. [source] Vulnerability of the superficial zone of immature articular cartilage to compressive injuryARTHRITIS & RHEUMATISM, Issue 10 2010Bernd Rolauffs Objective The zonal composition and functioning of adult articular cartilage causes depth-dependent responses to compressive injury. In immature cartilage, shear and compressive moduli as well as collagen and sulfated glycosaminoglycan (sGAG) content also vary with depth. However, there is little understanding of the depth-dependent damage caused by injury. Since injury to immature knee joints most often causes articular cartilage lesions, this study was undertaken to characterize the zonal dependence of biomechanical, biochemical, and matrix-associated changes caused by compressive injury. Methods Disks from the superficial and deeper zones of bovine calves were biomechanically characterized. Injury to the disks was achieved by applying a final strain of 50% compression at 100%/second, followed by biomechanical recharacterization. Tissue compaction upon injury as well as sGAG density, sGAG loss, and biosynthesis were measured. Collagen fiber orientation and matrix damage were assessed using histology, diffraction-enhanced x-ray imaging, and texture analysis. Results Injured superficial zone disks showed surface disruption, tissue compaction by 20.3 ± 4.3% (mean ± SEM), and immediate biomechanical impairment that was revealed by a mean ± SEM decrease in dynamic stiffness to 7.1 ± 3.3% of the value before injury and equilibrium moduli that were below the level of detection. Tissue areas that appeared intact on histology showed clear textural alterations. Injured deeper zone disks showed collagen crimping but remained undamaged and biomechanically intact. Superficial zone disks did not lose sGAG immediately after injury, but lost 17.8 ± 1.4% of sGAG after 48 hours; deeper zone disks lost only 2.8 ± 0.3% of sGAG content. Biomechanical impairment was associated primarily with structural damage. Conclusion The soft superficial zone of immature cartilage is vulnerable to compressive injury, causing superficial matrix disruption, extensive compaction, and textural alteration, which results in immediate loss of biomechanical function. In conjunction with delayed superficial sGAG loss, these changes may predispose the articular surface to further softening and tissue damage, thus increasing the risk of development of secondary osteoarthritis. [source] Supramolecular order following binding of the dichroic birefringent sulfonic dye Ponceau SS to collagen fibersBIOPOLYMERS, Issue 3 2005B. C. Vidal Abstract The optical anisotropies (linear dichroism or LD and birefringence) of crystalline aggregates of the sulfonic azo-dye Ponceau SS and of dye complexed with chicken tendon collagen fibers were investigated in order to assess their polarizing properties and similarity to liquid crystals. In some experiments, the staining was preceded by treatment with picric acid. Crystalline fibrous aggregates of the dye had a negative LD, and their electronic transitions were oriented perpendicular to the filamentary structures. The binding of Ponceau SS molecules to the collagen fibers altered the LD signal, with variations in the fiber orientation affecting the resulting dichroic ratios. The long axis of the rod-like dye molecule was assumed to be bound in register, parallel to the collagen fiber. Picric acid did not affect the oriented binding of the azo dye to collagen fibers. There were differences in the optical anisotropy of Ponceau SS-stained tendons from 21-day-old and 41-day-old chickens, indicating that Ponceau SS was able to distinguish between different ordered states of macromolecular aggregation in chicken tendon collagen fibers. In the presence of dichroic rod-like azo-dye molecules such as Ponceau SS, collagen also formed structures with a much higher degree of orientation. The presence of LD in the Ponceau SS-collagen complex even in unpolarized light indicated that this complex can act as a polarizer. © 2005 Wiley Periodicals, Inc. Biopolymers 78: 121,128, 2005 This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] Generalized Diffusion Tensor Imaging (GDTI): A Method for Characterizing and Imaging Diffusion Anisotropy Caused by Non-Gaussian DiffusionISRAEL JOURNAL OF CHEMISTRY, Issue 1-2 2003Chunlei Liu For non-Gaussian distributed random displacement, which is common in restricted diffusion, a second-order diffusion tensor is incapable of fully characterizing the diffusion process. The insufficiency of a second-order tensor is evident in the limited capability of diffusion tensor imaging (DTI) in resolving multiple fiber orientations within one voxel of human white matter. A generalized diffusion tensor imaging (GDTI) method was recently proposed to solve this problem by generalizing Fick's law to a higher-order partial differential equation (PDE). The relationship between the higher-order tensor coefficients of the PDE and the higher-order cumulants of the random displacement can be derived. The statistical property of the diffusion process was fully characterized via the higher-order tensor coefficients by reconstructing the probability density function (PDF) of the molecular random displacement. Those higher-order tensor coefficients can be measured using conventional diffusion-weighted imaging or spectroscopy techniques. Simulations demonstrated that this method was capable of quantitatively characterizing non-Gaussian diffusion and accurately resolving multiple fiber orientations. It can be shown that this method is consistent with the q-space approach. The second-order approximation of GDTI was shown to be DTI. [source] Cardiac diffusion MRI without motion effectsMAGNETIC RESONANCE IN MEDICINE, Issue 1 2002Jiangang Dou Abstract We present a method for diffusion tensor MRI in the beating heart that is insensitive to cardiac motion and strain. Using a stimulated echo pulse sequence with two electrocardiogram (ECG) triggers, diffusion-encoding bipolar gradient pulses are applied at identical phases in consecutive cardiac cycles. In this experiment, diffusion is encoded at a single phase in the cardiac cycle of less than 30 ms in duration. This encoding produces no phase shifts for periodic motion and is independent of intervening strains. Studies in a gel phantom with cyclic deformation confirm that by using this sequence we can map the diffusion tensor free of effects of cyclic motion. In normal human subjects, myocardial diffusion eigenvalues measured with the present method showed no significant change between acquisitions encoded at maximum contractile velocity (peak) vs. at myocardial standstill (end-systole), demonstrating motion independence of in vivo diffusion measurements. Diffusion tensor images acquired with the present method agree with registered data acquired with a previous cardiac diffusion MRI method that was shown to be valid in the normal heart, strongly supporting the validity of MRI diffusion measurement in the beating heart. Myocardial sheet and fiber dynamics measured during systole showed that normal human myocardial sheet orientations tilt toward the radial during systole, and fiber orientations tilt toward the longitudinal, in qualitative agreement with previous invasive studies in canines. These results demonstrate the technique's ability to measure myocardial diffusion accurately at any point in the cardiac cycle free of measurable motion effect, as if the heart were frozen at the point of acquisition. Magn Reson Med 48:105,114, 2002. © 2002 Wiley-Liss, Inc. [source] Two-component diffusion tensor MRI of isolated perfused heartsMAGNETIC RESONANCE IN MEDICINE, Issue 6 2001Edward W. Hsu Abstract Nonmonoexponential MR diffusion decay behavior has been observed at high diffusion-weighting strengths for cell aggregates and tissues, including the myocardium; however, implications for myocardial MR diffusion tensor imaging are largely unknown. In this study, a slow-exchange-limit, two-component diffusion tensor model was fitted to diffusion-weighted images obtained in isolated, perfused rat hearts. Results indicate that there are at least two distinct components of anisotropic diffusion, characterized by a "fast" component whose principal diffusivity is comparable to that of the perfusate, and a highly anisotropic "slow" component. It is speculated that the two components correspond to tissue compartments and have a general agreement with the orientations of anisotropy, or fiber orientations, in the myocardium. Moreover, consideration of previous studies of myocardial diffusion suggests that the presently observed fast component may likely be dominated by diffusion in the vascular space, whereas the slow component may include the intracellular and interstitial compartments. The implications of the results for myocardial fiber orientation mapping and limitations of the current two-component model used are also discussed. Magn Reson Med 45:1039,1045, 2001. © 2001 Wiley-Liss, Inc. [source] Influence of fiber orientation on high stress wear behavior of sisal fiber-reinforced epoxy compositesPOLYMER COMPOSITES, Issue 4 2007Navin Chand Sisal fiber-reinforced epoxy composites having three different fiber orientations, namely LL, LT, TT mentioned in the text were prepared and tested for their high stress abrasive wear behavior. Effect of fiber orientation, sliding distance, and load on abrasive wear of sisal,epoxy composites have been determined. Wear data of composites have been compared with the pure epoxy. Incorporation of fibers decreases the wear rate of epoxy resin, which varies with the fiber orientation. Wear rate in case of TT composite is found minimum as compared to other two composites. Wear rate follows the following trend, WTT < WLT < WLL. Owing to minimum exposed area of fiber to the sliding asperities, lowest wear rate occurs in the case of TT composite. Increase of load and sliding distance increases the wear volume in all the composites, because of the progressive loss of material. Wear mechanism has been discussed by using SEM micrographs of the worn surfaces. POLYM. COMPOS., 28:437,441, 2007. © 2007 Society of Plastics Engineers. [source] Short fibers suspension in steady recirculating flowsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2002Francisco Chinesta Abstract Numerical modeling of short fiber suspensions flows involves the coupling between motion equations, which definean elliptic problem, and the fluid constitutive equation, which introduces a non-linear advection problem related to the fiber orientation (induced anisotropy). In a previous work these authors have proposed a numerical procedure to determine a steady solution of the fibers orientation in steady recirculating flows, taking into account that neither initial nor boundary conditions are given. This procedure may be used in the numerical simulation of SFRT flows involving recirculating parts as encountered in the simulationof industrial processes, as well as in inverse rheological identification using, for example, rotative rheometric devices. La modélisation numérique des suspensions de fibres courtes implique le couplage entre les équations de mouvement (qui définissent un problème élliptique) et l'equation constitutive qui introduit un problème de transport non linéaire asocié à l'orientation des fibres. Les auteurs ont proposé, dans des travaux précédents, une technique numérique pour le calcul de l'orientation des fibres dans un écoulement stationnaire recirculant pour lequel les conditions aux limites et les conditions initiates ne sont pas connues. Cette technique peut être utilisée dans la simulation d'écoulements de fibres courtes présentant des recirculations, comme c'est le cas dans les écoulements industrielles en contraction ainsi que dans les instruments rhéométriques rotatifs. [source] | |||||||||||||||||||