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Fiber Layer (fiber + layer)
Kinds of Fiber Layer Terms modified by Fiber Layer Selected AbstractsExpression patterns of focal adhesion associated proteins in the developing retinaDEVELOPMENTAL DYNAMICS, Issue 4 2002Ming Li Abstract Adhesive interactions between integrin receptors and the extracellular matrix (ECM) are intimately involved in regulating development of a variety of tissues within the organism. In the present study, we have investigated the relationships between ,1 integrin receptors and focal adhesion associated proteins during eye development. We used specific antibodies to examine the distribution of ,1 integrin ECM receptors and the cytoplasmic focal adhesion associated proteins, talin, vinculin, and paxillin in the developing Xenopus retina. Immunoblot analysis confirmed antibody specificity and indicated that ,1 integrins, talin, vinculin, and paxillin were expressed in developing retina and in the retinal-derived Xenopus XR1 glial cell line. Triple-labeling immunocytochemistry revealed that talin, vinculin, paxillin, and phosphotyrosine proteins colocalized with ,1 integrins at focal adhesions located at the termini of F-actin filaments in XR1 cells. In the retina, these focal adhesion proteins exhibited developmentally regulated expression patterns during eye morphogenesis. In the embryonic retina, immunoreactivities for focal adhesion proteins were expressed in neuroepithelial cells, and immunoreactivity was especially strong at the interface between the optic vesicle and overlying ectoderm. At later stages, these proteins were expressed throughout all retinal layers with higher levels of expression observed in the plexiform layers, optic fiber layer, and in the region of the inner and outer limiting membrane. Strong immunoreactivities for ,1 integrin, paxillin, and phosphotyrosine were expressed in the radially oriented Müller glial cells at later stages of development. These results suggest that focal adhesion-associated proteins are involved in integrin-mediated adhesion and signaling and are likely to be essential in regulating retinal morphogenesis. © 2002 Wiley-Liss, Inc. [source] Retina development in zebrafish requires the heparan sulfate proteoglycan agrinDEVELOPMENTAL NEUROBIOLOGY, Issue 7 2008I-Hsuan Liu Abstract Recent studies from our laboratory have begun to elucidate the role of agrin in zebrafish development. One agrin morphant phenotype that results from agrin knockdown is microphthalmia (reduced eye size). To begin to understand the mechanisms underlying the role of agrin in eye development, we have analyzed retina development in agrin morphants. Retinal differentiation is impaired in agrin morphants, with retinal lamination being disrupted following agrin morpholino treatment. Pax 6.1 and Mbx1 gene expression, markers of eye development, are markedly reduced in agrin morphants. Formation of the optic fiber layer of the zebrafish retina is also impaired, exhibited as both reduced size of the optic fiber layer, and disruption of retinal ganglion cell axon growth to the optic tectum. The retinotectal topographic projection to the optic tectum is perturbed in agrin morphants in association with a marked loss of heparan sulfate expression in the retinotectal pathway, with this phenotype resembling retinotectal phenotypes observed in mutant zebrafish lacking enzymes for heparan sulfate synthesis. Treatment of agrin morphants with a fibroblast growth factor (Fgf) receptor inhibitor, rescue of the retinal lamination phenotype by transplantation of Fgf8-coated beads, and disruption of both the expression of Fgf-dependent genes and activation of ERK in agrin morphants provides evidence that agrin modulation of Fgf function contributes to retina development. Collectively, these agrin morphant phenotypes provide support for a crucial role of agrin in retina development and formation of an ordered retinotectal topographic map in the optic tectum of zebrafish. © 2008 Wiley Periodicals, Inc. Develop Neurobiol, 2008. [source] Distribution of neurotrophin-3 during the ontogeny and regeneration of the lizard (Gallotia galloti) visual systemDEVELOPMENTAL NEUROBIOLOGY, Issue 1 2008E. Santos Abstract We have previously described the spontaneous regeneration of retinal ganglion cell axons after optic nerve (ON) transection in the adult Gallotia galloti. As neurotrophin-3 (NT-3) is involved in neuronal differentiation, survival and synaptic plasticity, we performed a comparative immunohistochemical study of NT-3 during the ontogeny and regeneration (after 0.5, 1, 3, 6, 9, and 12 months postlesion) of the lizard visual system to reveal its distribution and changes during these events. For characterization of NT-3+ cells, we performed double labelings using the neuronal markers HuC-D, Pax6 and parvalbumin (Parv), the microglial marker tomato lectin or Lycopersicon esculentum agglutinin (LEA), and the astroglial markers vimentin (Vim) and glial fibrillary acidic protein (GFAP). Subpopulations of retinal and tectal neurons were NT-3+ from early embryonic stages to adulthood. Nerve fibers within the retinal nerve fiber layer, both plexiform layers and the retinorecipient layers in the optic tectum (OT) were also stained. In addition, NT-3+/GFAP+ and NT-3+/Vim+ astrocytes were detected in the ON, chiasm and optic tract in postnatal and adult lizards. At 1 month postlesion, abundant NT-3+/GFAP+ astrocytes and NT-3,/LEA+ microglia/macrophages were stained in the lesioned ON, whereas NT-3 became downregulated in the experimental retina and OT. Interestingly, at 9 and 12 months postlesion, the staining in the experimental retina resembled that in control animals, whereas bundles of putative regrown fibers showed a disorganized staining pattern in the OT. Altogether, we demonstrate that NT-3 is widely distributed in the lizard visual system and its changes after ON transection might be permissive for the successful axonal regrowth. © 2007 Wiley Periodicals, Inc. Develop Neurobiol, 2008 [source] In utero exposure to vigabatrin: No indication of visual field lossEPILEPSIA, Issue 2 2009Charlotte Lawthom Summary The purpose of the study was to determine whether in utero exposure to vigabatrin caused visual field loss. Three mothers with four children who had been exposed to vigabatrin in utero and who were subsequently formula fed were identified. All seven individuals underwent perimetry and imaging of the retinal nerve fiber layer (RNFL). All individuals yielded reliable outcomes to perimetry and RNFL images of acceptable quality. Two of the three mothers exhibited vigabatrin-attributed visual field loss and an abnormally attenuated RNFL. The third exhibited an upper left quadrantanopia, consistent with previous temporal lobe surgery, and a normal RNFL. All four children yielded normal visual fields and RNFL thicknesses. The presence of the normal findings for the children is reassuring and, if representative, suggests a lack of vigabatrin visual toxicity and therefore obviates the need for ophthalmological examination of those exposed to vigabatrin prenatally. [source] Distribution and morphology of serotonin-immunoreactive axons in the hippocampal region of the New Zealand white rabbit.HIPPOCAMPUS, Issue 1 2003Abstract This study provides a detailed light microscopic description of the morphology and distribution of immunohistochemically stained serotonergic axons in the hippocampal region of the New Zealand white rabbit. The serotonergic axons were segregated morphologically into three types: beaded fibers, fine fibers, and stem-axons, respectively. Beaded fibers were thin serotonergic axons with large varicosities, whereas thin axons with small fusiform or granular varicosities were called fine fibers. Finally, thick straight non-varicose axons were called stem-axons. Beaded fibers often formed large conglomerates with numerous boutons (pericellular arrays) in close apposition to the cell-rich layers in the hippocampal region, e.g., the granular and hilar cell layers of the dentate area and the pyramidal cell layer ventrally in CA3. The pericellular arrays in these layers were often encountered in relation to small calbindin-D28K -positive cells, as shown by immunohistochemical double staining for serotonin and calbindin-D28K. The beaded and fine serotonergic fibers displayed a specific innervation pattern in the hippocampal region and were encountered predominantly within the terminal field of the perforant path, e.g., the stratum moleculare hippocampi and the outer two-thirds of the dentate molecular layer. These fibers were also frequently seen in the deep part of the stratum oriens and the alveus, forming a dense plexus in relation to large multipolar calbindin-D28K -positive cells and their basal extensions. Stem-axons were primarily seen in the fimbria and alveus. This innervation pattern was present throughout the entire hippocampal formation, but there were considerable septotemporal differences in the density of the serotonergic innervation. A high density of innervation prevailed in the ventral/temporal part of the hippocampal formation, whereas the dorsal/septal part received only a moderate to weak serotonergic innervation. These results suggest that the serotonergic system could modulate the internal hippocampal circuitry by way of its innervation in the terminal field of the perforant path, the hilus fasciae dentatae, and ventrally in the zone closely apposed to the mossy fiber layer and the pyramidal cells of CA3. This modulation could be of a dual nature, mediated directly by single serotonergic fibers traversing the hippocampal layers or indirectly by the pericellular arrays and their close relation to the calbindin-D28K -positive cells. The marked septotemporal differences in innervation density point toward a difference between the ventral and dorsal parts of the hippocampal formation with respect to serotonergic function and need for serotonergic modulation. Hippocampus 2003;13:21,37. © 2003 Wiley-Liss, Inc. [source] Longitudinal study of vision and retinal nerve fiber layer thickness in multiple sclerosisANNALS OF NEUROLOGY, Issue 6 2010Lauren S. Talman BA Objective Cross-sectional studies of optical coherence tomography (OCT) show that retinal nerve fiber layer (RNFL) thickness is reduced in multiple sclerosis (MS) and correlates with visual function. We determined how longitudinal changes in RNFL thickness relate to visual loss. We also examined patterns of RNFL thinning over time in MS eyes with and without a prior history of acute optic neuritis (ON). Methods Patients underwent OCT measurement of RNFL thickness at baseline and at 6-month intervals during a mean follow-up of 18 months at 3 centers. Low-contrast letter acuity (2.5%, 1.25% contrast) and visual acuity (VA) were assessed. Results Among 299 patients (593 eyes) with ,6 months follow-up, eyes with visual loss showed greater RNFL thinning compared to eyes with stable vision (low-contrast acuity, 2.5%: p < 0.001; VA: p = 0.005). RNFL thinning increased over time, with average losses of 2.9,m at 2 to 3 years and 6.1,m at 3 to 4.5 years (p < 0.001 vs 0.5,1-year follow-up interval). These patterns were observed for eyes with or without prior history of ON. Proportions of eyes with RNFL loss greater than test-retest variability (,6.6,m) increased from 11% at 0 to 1 year to 44% at 3 to 4.5 years (p < 0.001). Interpretation Progressive RNFL thinning occurs as a function of time in some patients with MS, even in the absence of ON, and is associated with clinically significant visual loss. These findings are consistent with subclinical axonal loss in the anterior visual pathway in MS, and support the use of OCT and low-contrast acuity as methods to evaluate the effectiveness of putative neuroprotection protocols. ANN NEUROL 2010;67:749,760 [source] Axonal loss and myelin in early ON loss in postacute optic neuritisANNALS OF NEUROLOGY, Issue 3 2008Alexander Klistorner PhD Objective To investigate the relation between retinal nerve fiber layer (RNFL) thickness and latency and amplitude of multifocal visual-evoked potentials (mfVEPs) in the postacute stage of optic neuritis in patients with early or possible multiple sclerosis. Method Thirty-two patients with clinical diagnosis of unilateral optic neuritis and magnetic resonance imaging lesions typical of demyelination and 25 control subjects underwent mfVEP and optical coherence tomography imaging. Results Although there was significant reduction of RNFL thickness in the affected eyes (18.7%), a considerably larger decrease was observed for the amplitude of the mfVEPs (39.8%). Latency of the mfVEPs was also significantly delayed in optic neuritis eyes. In fellow eyes, the amplitude of mfVEPs was significantly reduced and the latency prolonged, but RNFL thickness remained unaltered. RNFL thickness correlated highly with the mfVEP amplitude (r = 0.90). There was also strong correlation between optical coherence tomography measure of axonal loss and mfVEP latency (r = ,0.66). Interpretation Although our findings demonstrate strong associations between structural and functional measures of optic nerve integrity, the functional loss was more marked. This fact, together with amplitude and latency changes of the mfVEPs observed in clinically normal fellow eyes, may indicate greater sensitivity of mfVEPs in detecting optic nerve abnormality or the presence of widespread inflammation in the central nervous system, or both. The significant correlation of the mfVEP latency with RNFL thickness suggests a role for demyelination in promoting axonal loss. Ann Neurol 2008 [source] 2453: Optic disc in the picture: novel imaging techniquesACTA OPHTHALMOLOGICA, Issue 2010W DREXLER Purpose Advances in light sources and detection technologies enabled a paradigm shift in retinal OCT imaging performance. ,Snap-shot OCT' enabling isotropic sampling over 512x512x1024 voxels with 600 frames/second in less than a second is now possible. Methods The resolution advantage in conjunction with full volumetric sampling has enabled the development of more informative indices of axonal damage in glaucoma compared with measurements of RNFL thickness and cup to disc ratio provided by other devices. A novel mapping method was developed, the three-dimensional minimal distance (3D-MDM) as the optical correlate of true retinal nerve fiber layer thickness around the optic nerve head region. In a preliminary study relation between the cross-sectional areas of the retinal nerve fiber layer and the optic nerve was found to be a sensitive measure of axon loss. Results In addition to all the major layers of the retina, the entire choroid down to the lamina cribrosa and sclera can now be visualized. This enables unprecedented information about choroidal vasculature without any contrast agents, choroidal thickness and will enable quantification of choroidal blood flow in the near future. Furthermore this technique allows tissue to be imaged in vitro with an image resolution better than 1-2 µm, allowing to image single cells and detect pre-apoptotic signatures using OCT. RGC-5 cells were imaged using a sampling rate 1024x512x1024 voxel at 800 nm central wavelength and a bandwidth of 230 nm, enabling the detection of optical signatures at different pre-stages of programmed cell death. Conclusion Significantly increased OCT imaging speed and tissue penetration might enable novel insights and diagnostic opportunities in the diagnosis and therapy monitoring of glaucoma. Commercial interest [source] Segmentation of FD-OCT images shows selective loss of inner retinal layers in patients with DM and no or early DRACTA OPHTHALMOLOGICA, Issue 2009FD VERBRAAK Purpose Determine whether diabetes differentially affects specific retinal layers by comparing the thickness of six retinal layers in diabetic patients with no or minimal diabetic retinopathy (DR) to age- and gender-matched normal controls. Methods Forty-four patients with type 1 diabetes and no or minimal DR underwent full ophthalmic examination, stereoscopic fundus photographs and spectral domain optical coherence tomography (OCT). Following automated segmentation of intraretinal layers of the OCT images, mean thickness was calculated for 6 individual layers of the retina in the fovea, the pericentral area and the peripheral area of the central macula and compared to an age- and gender-matched control group. Results In type 1 diabetic patients with minimal DR, the retinal nerve fiber layer (p=0.00) and the ganglion cell/inner plexiform layer (p=0.02) were significantly thinner compared to age- and gender-matched controls. No other layers showed a significant difference. Conclusion Thinning of the total retina in diabetic patients with minimal DR relative to normal controls is due to a selective thinning of inner retinal layers and supports the concept that early DR includes a neuro-degenerative component. [source] Relationship between standard automated perimetry and high-resolution optical coherence tomography in glaucoma patientsACTA OPHTHALMOLOGICA, Issue 2009P CALVO PEREZ Purpose To determine the relationship between the main indices of standard automated perimetry (SAP) and the peripapillary retinal nerve fiber layer (RNFL) thickness measured with spectral-domain optical coherence tomography (OCT) in patients with glaucomatous visual field defects. Methods 47 consecutive patients with open-angle glaucoma were included in the study. Only one eye per subject was randomly selected. SAPs were performed with a Humphrey perimeter and the 24-2 SITA standard algorithm. All of them underwent imaging with the Spectralis OCT (Heidelberg Engineering, Heidelberg, Germany). Left eye data were converted to a right eye format. The Kolmogorov Smirnov test was applied to check that the data were normally distributed. Pearson correlations were calculated between SAP indices (mean deviation, pattern standard deviation, and visual field index) and OCT parameters Results The average visual field mean deviation was -6.50 dB. Mild to moderate correlations were observed between SAP indices and most OCT parameters. The strongest correlations were found between the inferior quadrant thickness and pattern standard deviation (-0.544). Conclusion The RNFL thicknesses measured with high-resolution OCT showed moderate correlations with SAP indices in glaucoma patients. These results may help to understand the relationship between structural and functional changes in open-angle glaucoma. [source] Retinal nerve fiber layer thickness and central corneal thickness in ocular hypertensive patients and healthy subjectsACTA OPHTHALMOLOGICA, Issue 2009AM BRON Purpose To establish the correlation between central corneal thickness (CCT) and retinal nerve fiber layer (RNFL) thickness in ocular hypertensive patients and healthy subjects. Methods We prospectively collected charts of healthy subjects and ocular hypertensive (OHT) patients in one academic center between 2007 and 2008. OHT patients were defined by two measurements of intraocular pressure superior to 21mmHg without treatment, open angle in gonioscopy, normal appearing optic nerve head and normal visual field test Standard Automated Perimetry (SAP SITA) and Frequency Doubling Technique (FDT). Every patient underwent a standard clinical examination including optic nerve head examination, intraocular pressure, CCT measurement by ultrasonic (US) and anterior segment OCT pachymetry, visual field testing (SAP and FDT), RNFL thickness by scanning laser polarimetry (GDX-VCC) and optical coherence tomography (OCT). Results Eighty healthy subjects and 60 OHT patients were included. A correlation between US CCT and OCT CCT was found in both groups (r2=0.85 and r2= 0.87, p<0.001). There was no significant difference (p>0.15) in GDX-VCC and OCT RNFL thickness in both groups. In controls there was no correlation of any RNFL thickness measurement with the CCT. In OHT patients, the US CCT was weakly correlated with the average TSNIT evaluated by GDX-VCC (r2= 0.04, p<0.02). Conclusion This study did not show any relevant correlation between the RNFL thickness evaluated by GDX-VCC and the US CCT in healthy individuals and in OHT patients with a normal FDT. [source] The retinal nerve fiber layer and the optic nerve head morphology after glaucoma surgeryACTA OPHTHALMOLOGICA, Issue 2009T GRACNER Purpose To detect and quantify changes in the retinal nerve fiber layer (RNFL) and the optic nerve head (ONH) morphology after glaucoma surgery. Methods 13 eyes of 13 patients with open-angle glaucoma in which goniotrephining with scleral flap without intraoperative antimetabolites for progressive glaucoma damage was done were included in this prospective study. Before and 6 months after the surgery: the intraocular pressure (IOP) was measured, the thicknes of the RNFL was measured with a scanning laser polarimeter (GDx VCC), the confocal scanning laser ophthalmoscopy measurements of ONH with Heidelberg retina tomograph (HRT 3) were performed and the visual field was tested with Humphrey Field Analyser. Results The mean IOP before surgery was 24.5 ? 2.3 mmHg decreasing 6 months after to a mean of 13.9 ? 3.0 mmHg (p<0.05). The RNFL measurements with GDx VCC revealed no differences between the mean TSNIT Avarage (p=0.383), mean Superior Avarage (p=0.756) and mean Inferior Avarage (p=0.269) before and after surgery. The ONH measurements with HRT 3 revealed postoperatively a significant increase in the mean Rim Area, Rim Volume and Cup Shape Measure, whereas Cup Area, Cup Volume and Linear Cup/Disc Ratio decreased (p<0.05). There were no differences between the mean Height Variation Contour (p=0.678) and Mean RNFL Thickness (p=0.064) before and after surgery. Preoperatively the mean value of the Mean Deviation on automated perimetry was ,18.82 ? 8.5 dB improving 6 months postoperatively to a mean of ,16.63 ? 7.9 dB (p<0.05). Conclusion Our study demonstrated the beneficial effect of IOP reduction obtained with glaucoma surgery on visual field indices and ONH parameters evaluated by HRT 3. [source] Toxic effect of vigabatrin on retinal nerve fiber layerACTA OPHTHALMOLOGICA, Issue 2009A MIDELFART Purpose To investigate whether peripheral and central visual field defects detected among epilepsy patients treated with vigabatrin are associated with reduced peripapillary retinal nerve fiber layer thickness as measured with optic coherence tomography (OCT). Methods Nine epilepsy patients with vigabatrin-attributed visual field loss (group 1) and seven patients(age and sex matched) with epilepsy treated with other drugs(control group 2) were regularly examined with automated perimetry up to 60 degrees from fixation point (Humphrey Field Analyser). Peripapillary retinal nerve fiber layer thickness (RNFLT) was quantified by optic coherence tomography (OCT) using Fast RNFLT protocol, Stratus OCT (3.0). Five of the patients in group 1 had peripheral visual field defects, (group 1a), four had a central field defect(group 1b). All patients in control group 2 had normal visual field. Results Patients with vigabatrin-attributed visual field loss had attenuated total RNFLT compared to controls (right eye : mean total RNFLT: group 1: 75.6 µm (SD 12.7); group 2: 103.5 µm (SD 9.7), mean difference 27.9 µm (CI 15.9-39.9;P < 0.001). The nasal and inferior sectors RNFLT were more attenuated in patients with vigabatrin-attributed visual field loss compared to controls, while no difference was detected in the temporal RNFLT. Both individuals with peripheral and central visual field losses had attenuated mean total RNFLT compared to controls (P = 0.006 and P= 0.002, respectively). Conclusion Vigabatrin-attributed visual field defects are associated with reduced RNFLT. Combination of perimetry and OCT can efficiently detect vigabatrin induced retinal nerve fiber damage. [source] Monitoring retinal ganglion cells in vivoACTA OPHTHALMOLOGICA, Issue 2008M PAQUES Progress in imaging techniques will considerably increase our knowledge on retinal cell pathophysiology and death during optic nerve disesases as a whole. Experimentally, current in vivo imaging using the green laser reflectance mode of the SLO allows noninvasive microscopic-scale definition of the nerve fibers. However, loss of the axons is a late and irreversible event, thus imaging the retinal ganglion cells themselves would be preferable in order to detect diseased states at an earlier stage. Retrogradelly-labelled RGCs can be conveniently seen in vivo, but such imaging require invasive procedures, the effect of which on RGC physiology remains uncertain. The recent development of molecular imaging of apoptotic ganglion cells is promising. The cSLO also allows in vivo imaging of other cellular compartments that are relevant for glaucoma, for instance microglial cells. In humans, current techniques allow imaging of the nerve fiber layer with a relatively low resolution. The GDx evaluates the nerve fiber layer thickness through light polarisation, and high resolution OCT through mapping of its thickness around the optic nerve. Yet, it is likely that these systems lack sensitivity for detection of the early loss of the NFL, and even more for early dysfunction of RGCs. Presently, adaptive optics does not appear to be a technique of choice for the NFL, but technological progress may prove this assertion to be wrong. In the future, techniques allowing increased contrast of fibrillar structures such as en face OCT may prove of interest. [source] An evaluation of the retinal nerve fiber layer thickness by scanning laser polarimetry in individuals with dementia of the Alzheimer typeACTA OPHTHALMOLOGICA, Issue 2 2001Hélène Kergoat ABSTRACT. Purpose: To determine, using scanning laser polarimetry, whether or not the retinal nerve fiber layer (RNFL) is altered in dementia of the Alzheimer type (DAT). Methods: Thirty individuals with mild to moderate DAT and 30 healthy age-matched controls participated in the study. Fundus images were acquired with a Nerve Fiber Analyzer. RNFL thickness measurements were obtained under an ellipse located 1.75 disc diameter from the optic nerve head (ONH) center. Results: No differences in RNFL thickness were observed between DAT and healthy subjects. The regional distribution of RNFL thickness was similar between the two test groups, with the RNFL being thickest in the superior and inferior retinal segments relative to the nasal and temporal regions. Conclusions: Our data indicate that the RNFL is not altered in DAT, at least in the earlier stages of the disease. [source] An ultrastructural study of the cuticle in the marine annelid Heterodrilus (Tubificidae, Clitellata)JOURNAL OF MORPHOLOGY, Issue 1 2008Erica Sjölin Abstract The ultrastructure of the cuticle in four species of the marine Heterodrilus (H. paucifascis, H. pentcheffi, H. flexuosus, H. minisetosus) is investigated with transmission electron microscopy. The noncellular cuticle consists of several parts; closest to the epidermis is a thick zone of collagen fibers embedded in a matrix. The matrix continues outside the fiber zone, forming a layered epicuticle. The external surface of the epicuticle is covered by evenly distributed, membrane-bound bodies, termed epicuticular projections. The epicuticular projections have their longitudinal axis perpendicular to the surface of the cuticle and are attached to the surface by either the surrounding membrane itself or by short pedestals. Microvilli, extensions from the epidermal cells, penetrate and sometimes pass completely through the cuticle. There is interspecific variation in the morphology of the cuticle. The four studied species differ in the arrangement of the collagen fibers, from irregularly distributed fibril bundles to orthogonally arranged fiber layers, as well as in the number and density of layers in the epicuticle. One of the studied species, H. paucifascis, shows intraspecific variation, which is associated with sample locality. The Bahamian specimens of H. paucifascis have four layers in the epicuticle, club-shaped epicuticular projections, and collagen fibers forming a less defined orthogonal grid, while the Belizean specimens have three layers in the epicuticle, epicuticular projections with a bulging part at midlevel, and a distinct orthogonal grid. Based on these findings the variation in the morphology of the cuticle appears to be dependent on both phylogenetic constraints, and functional and environmental factors. J. Morphol., 2008. © 2007 Wiley-Liss, Inc. [source] Compaction of fiber reinforcementsPOLYMER COMPOSITES, Issue 3 2002Gibson L. Batch In resin transfer molding, dry fiber reinforcements are compacted as the mold closes before injection of a curable resin matrix. This paper presents experimental data of compaction pressure as a function of fiber volume fraction. Data are presented for woven roving mats, random fiber mats, loose fiber rovings for pultrusion, and uniaxial or biaxial roving mats. These data are fit to a mathematical model derived in an Appendix. Experimental data are also given for six combinations of reinforcements. We use the compaction model of each constituent layer to predict the average volume fraction assuming that fiber layers do not interact. However, we see that most combinations of reinforcements have fiber volume fractions greater than expected at pressures under 50 psi, indicating a synergistic packing between the layers of different composition. [source] | |||||||||||||