Academic literature on the topic 'Disc height'
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Journal articles on the topic "Disc height"
1
Zheng, Jun, and CaiLiang Shen. "Quantitative Relationship between the Degree of Lumbar Disc Degeneration and Intervertebral Disc Height in Patients with Low Back Pain." Contrast Media & Molecular Imaging 2022 (July 19, 2022): 1–6. http://dx.doi.org/10.1155/2022/5960317.
Full textAbstract:
The aim of this study is to study the relationship between the degree of lumbar disc degeneration and the height of the disc in patients with pain in the lower back and determine whether there is a dose-response relationship between the two. Eighty-five patients were examined by magnetic resonance imaging (MRI). The grade of lumbar degeneration was determined by the Pfirrmann grading system, and the intervertebral height and VAS pain scores were measured. The height difference of intervertebral discs with different degeneration levels was measured by the F test. This difference was correlated and further quantified by regression analysis. Finally, the differences intervertebral disc heights with a VAS score of 0–6 and 7–10 were observed by an independent sample t-test. The higher degree of disc degeneration in each lumbosacral segment, the lower the intervertebral disc height p ≤ 0.011 . When discs with grade 1 and grade 5 degeneration were excluded, the results remained the same p ≤ 0.034 . To quantify correlations, at each lumbar level, the disc height was reduced for each level of lumbosacral disc degeneration, and the height of disc was reduced after adjusting according to age, sex, and BMI (β range: −1.25 mm to −1.76 mm, 95% CI: −0.83 to −2.29, all p ≤ 0.002 ). Subjects with a VAS score of 7–10 had a lower intervertebral disc height than those with a VAS score of 0–6, especially with respect to total height levels at L4/5, L5/S1, and L1-S1 p ≤ 0.04 . This study showed a relationship between increased degree of intervertebral disc degeneration and decreased the disc height in patients with pain in the low back. Although the assessment of lumbar and lumbosacral level disc degeneration involves many qualitative measurements, these statistical data confirm the effectiveness of lumbosacral disc height as a continuous data measure and quantification in clinical trials and epidemiological studies.
2
Agichani, Sonali Rajesh, Subhash D. Joshi, and Sharda Subhash Joshi. "Morphometric Study of Lumbar Intervertebral Discs in a Tertiary Care Centre in Central India." Journal of Evidence Based Medicine and Healthcare 8, no. 31 (August 2, 2021): 2895–99. http://dx.doi.org/10.18410/jebmh/2021/529.
Full textAbstract:
BACKGROUND The intervertebral disc (IVD) is the primary load-bearing structure in the vertebral column. It is avascular, has low metabolic rate and hence most vulnerable to damage. One of the most important causes of low back pain is the disc lesions. Hence, the present study was done to provide morphometric data of lumbar intervertebral discs in central Indians. METHODS Anterior and posterior heights of lumbar intervertebral discs were measured in (a) 10 cadavers by digital vernier calipers; (b) 120 normal, lateral view digital radiographs divided in three age groups in both the sexes, digitally. RESULTS Average heights of lumbar intervertebral discs were recorded as follows: (a) Average anterior height, measured in centimeters, was: In cadavers, L1/2-0.7922, L2/3-0.9139, L3/4-1.0611, L4/5-1.2569, and L5/S1- 1.2565 cms. On digital radiographs, L1/2-1.023, L2/3-1.262, L3/4-1.433, L4/5-1.691, L5/S1- 1.763 cms. (b) Average posterior height, measured in centimeters, was: In cadavers, L1/2-0.4624, L2/3-0.4925, L3/4-0.5872, L4/5-0.6546, and L5/S1- 0.4997cms. On digital radiographs, L1/2-0.78475, L2/3-0.875917, L3/4-0.900083, L4/5- 0.92375, and L5/S1-0.795 cms. CONCLUSIONS Average anterior heights are more than posterior heights. Average anterior and posterior heights increase from L1/2 upto L4/5, then decrease at L5/S1. But in digital radiographs, average anterior height increases from L1/2 to L5/S1. The difference in measurements of average anterior heights of L1/2 disc is found to be statistically significant with respect to age. Gender difference is statistically significant at different disc levels in different age groups. The present study will help to generate baseline data to detect abnormality and to make population specific prosthesis for treatment of disc lesions. KEYWORDS Morphometry, Lumbar Intervertebral Discs
3
Wilke, Hans-Joachim, Sinead Kavanagh, Sylvia Neller, Christian Haid, and Lutz Eberhart Claes. "Effect of a prosthetic disc nucleus on the mobility and disc height of the L4–5 intervertebral disc postnucleotomy." Journal of Neurosurgery: Spine 95, no. 2 (October 2001): 208–14. http://dx.doi.org/10.3171/spi.2001.95.2.0208.
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Object. Current procedures for treatment of degenerative disc disease may not restore flexibility or disc height to the intervertebral disc. Recently, a prosthetic device, intended to replace the degenerated nucleus pulposus, was developed. In this biomechanical in vitro test the authors study the effect of implanting a prosthetic nucleus in cadaveric lumbar intervertebral discs postnucleotomy and determine if the flexibility and disc height of the L4–5 motion segment is restored. Methods. The prosthetic disc nucleus device consists of two hydrogel pellets, each enclosed in a woven polyethylene jacket. Six human cadaveric lumbar motion segments (obtained in individuals who, at the time of death, were a mean age of 56.7 years) were loaded with moments of ± 7.5 Nm in flexion—extension, lateral bending, and axial rotation. The following states were investigated: intact, postnucleotomy, and after device implantation. Range of motion (ROM) and neutral zone (NZ) measurements were determined. Change in disc height from the intact state was measured after nucleotomy and device implantation, with and without a 200-N preload. Conclusions. Compared with the intact state (100%), the nucleotomy increased the ROM in flexion—extension to 118%, lateral bending to 112%, and axial rotation to 121%; once the device was implanted the ROM was reduced to 102%, 88%, and 90%, respectively. The NZ increased the ROM to 210%, lateral bending to 173%, and axial rotation to 107% after nucleotomy, and 146%, 149%, 44%, respectively, after device implantation. A 200-N preload reduced the intact and postnucleotomy disc heights by approximately 1 mm and 2 mm, respectively. The original intact disc height was restored after implantation of the device. The results of the cadaveric L4–5 flexibility testing indicate that the device can potentially restore ROM, NZ, and disc height to the denucleated segment.
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Jeong, Jae-Gyeong, Sungwook Kang, Gu-Hee Jung, Mingoo Cho, Hyunsoo Kim, Kyoung-Tae Kim, Dong-Hee Kim, and Jong-Moon Hwang. "Biomechanical Effect of Disc Height on the Components of the Lumbar Column at the Same Axial Load: A Finite-Element Study." Journal of Healthcare Engineering 2022 (October 25, 2022): 1–13. http://dx.doi.org/10.1155/2022/7069448.
Full textAbstract:
Intervertebral discs are fibrocartilage structures, which play a role in buffering the compression applied to the vertebral bodies evenly while permitting limited movements. According to several previous studies, degenerative changes in the intervertebral disc could be accelerated by factors, such as aging, the female sex, obesity, and smoking. As degenerative change progresses, the disc height could be reduced due to the dehydration of the nucleus pulposus. This study aimed to quantitatively analyze the pressure that each structure of the spine receives according to the change in the disc height and predict the physiological effect of disc height on the spine. We analyzed the biomechanical effect on spinal structures when the disc height was decreased using a finite-element method investigation of the lumbar spine. Using a 3D FE model, the degree and distribution of von-Mises stress according to the disc height change were measured by applying the load of four different motions to the lumbar spine. The height was changed by dividing the anterior and posterior parts of the disc, and analysis was performed in the following four motions: flexion, extension, lateral bending, and axial rotation. Except for a few circumstances, the stress applied to the structure generally increased as the disc height decreased. Such a phenomenon was more pronounced when the direction in which the force was concentrated coincided with the portion where the disc height decreased. This study demonstrated that the degree of stress applied to the spinal structure generally increases as the disc height decreases. The increase in stress was more prominent when the part where the disc height was decreased and the part where the moment was additionally applied coincided. Disc height reduction could accelerate degenerative changes in the spine. Therefore, eliminating the controllable risk factors that cause disc height reduction may be beneficial for spinal health.
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Tumialán, Luis M., Justin C. Clark, Laura A. Snyder, and Frederick F. Marciano. "Provisional Ipsilateral Expandable Rod for Disc Space Distraction in Minimally Invasive Transforaminal Lumbar Interbody Fusion: Operative Technique." Operative Neurosurgery 10, no. 4 (August 25, 2014): 555–64. http://dx.doi.org/10.1227/neu.0000000000000542.
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Abstract BACKGROUND: Lumbar disc degeneration may be so advanced and asymmetrical that transforaminal access to the interbody space is limited. The extent of collapse may compromise the capacity to restore disc height and coronal balance in minimally invasive approaches. Although a variety of distractors are available for open approaches, currently there is no feasible distractor that is functional within a minimally invasive retractor. OBJECTIVE: To describe the development of a provisional ipsilateral expandable rod for use in minimally invasive surgery for transforaminal lumbar interbody fusions to optimize access to the disc space, thereby facilitating placement of an interbody spacer. METHODS: The authors report the clinical and radiographic data for 30 patients (3 open and 27 minimally invasive surgeries) with advanced degenerative disc disease in whom a provisional ipsilateral expandable rod was used to restore coronal balance and maintain disc height for interbody preparation and placement. Preoperative disc heights were measured, and the height of interbody spacer recorded. Mean restoration of disc heights was calculated. RESULTS: The provisional ipsilateral expandable rod was successfully applied in both open exposures and within a minimally invasive retractor. The mean preoperative disc height was 4.9 mm (range, 1-9 mm), the mean height of the spacer inserted was 11.1 mm (range, 8-15 mm), and the mean increase in disc height was 6.2 mm (range, 5-11 mm). CONCLUSION: A provisional ipsilateral expandable rod is feasible in either minimally invasive or open approaches. It has the capacity to maintain the disc height achieved by paddle distractors. This facilitates both the disc preparation and optimizes restoration of disc height and interbody spacer placement.
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Liu, Ming Yu, Yin Bang Liu, and Li Chun Jiang. "Variation of Wood Density in Larch in Northeast of China." Advanced Materials Research 487 (March 2012): 38–42. http://dx.doi.org/10.4028/www.scientific.net/amr.487.38.
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Wood density was investigated in seven dahurian larch (Larix gmelinii Rupr.) trees grown in northeastern China. Six discs (about 5 cm thick) were cut from each tree (i.e. from the root stem, at breast height (1.3m), and at 20%, 40%, 60%, and 80% of the total height). For each disc, a thick sliver with parallel sides was cut out along the diameter of the disc. The sliver was about 40-mm thick, with the pith located in the middle. Eight small pieces were cut from the sliver with equal distance from pith to bark. Wood density of small piece was obtained using water displacement method. Significant variation in wood density was observed among sections for different heights. Wood density increases from pith to bark for all height categories and decreases from the stump to top of the tree height.
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Ding, Huaili, Lijun Liao, Peichun Yan, Xiaolin Zhao, and Min Li. "Three-Dimensional Finite Element Analysis of L4-5 Degenerative Lumbar Disc Traction under Different Pushing Heights." Journal of Healthcare Engineering 2021 (July 19, 2021): 1–9. http://dx.doi.org/10.1155/2021/1322397.
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Objective. To study and analyze the changes of intervertebral foramen height and area of the degenerative L4-5 intervertebral disc under different pushing heights by the finite element method. Methods. CT and MRI images of T12-S1 segments were obtained from a healthy volunteer who met the inclusion criteria. A DR machine was used to capture images of the lumbar lateral section before and after simultaneous pushing of the L4 and L5 spinous processes by manipulation called Daogaijinbei, and the measurement showed that the displacement changes of L4 and L5 were both approximately 10 cm, so the pushing height was set at 0–10 cm. A three-dimensional finite element model of the entire normal lumbar spine was established using Mimics 16.0, Geomagic Studio 2014, Hypermesh 13.0, MSC.Patran 2012, and so on. The disc height and nucleus area of the lumbar disc of the normal entire lumbar disc model were adjusted to establish models of the L4-5 disc with mild, moderate, and severe degeneration. Changes of disc height and area of the L4-5 degenerative intervertebral disc under different pushing heights were calculated. Results. The size of the L4-5 intervertebral foramen was analyzed from the height and area of the intervertebral foramen, and the results showed the following: (1) as for the normal lumbar disc and a lumbar of the L4-5 disc with mild and moderate degeneration, the height of the L4-5 intervertebral foramen and its area both increased during pushing between 0 and 8 cm. After the pushing height reached 8 cm, the height and area of the L4-5 intervertebral foramen gradually became stable; (2) as for the L4-5 disc with severe degeneration, during the process of pushing, the height and area of the L4-5 intervertebral foramen increased slightly, but this change was not obvious. Conclusions. After the spinal manipulation, the sizes of the L4-5 intervertebral foramen of the L4-5 disc with mild and moderate degeneration were significantly larger than those before pushing; in contrast, the size of L4-5 intervertebral foramen of the L4-5 disc with severe lumbar degeneration was not significantly changed.
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Friedmann, Andrea, Andre Baertel, Christine Schmitt, Christopher Ludtka, Javorina Milosevic, Hans-Joerg Meisel, Felix Goehre, and Stefan Schwan. "Intervertebral Disc Regeneration Injection of a Cell-Loaded Collagen Hydrogel in a Sheep Model." International Journal of Molecular Sciences 22, no. 8 (April 19, 2021): 4248. http://dx.doi.org/10.3390/ijms22084248.
Full textAbstract:
Degenerated intervertebral discs (IVDs) were treated with autologous adipose-derived stem cells (ASC) loaded into an injectable collagen scaffold in a sheep model to investigate the implant’s therapeutic potential regarding the progression of degeneration of previously damaged discs. In this study, 18 merino sheep were subjected to a 3-step minimally invasive injury and treatment model, which consisted of surgically induced disc degeneration, treatment of IVDs with an ASC-loaded collagen hydrogel 6 weeks post-operatively, and assessment of the implant’s influence on degenerative tissue changes after 6 and 12 months of grazing. Autologous ASCs were extracted from subcutaneous adipose tissue and cultivated in vitro. At the end of the experiment, disc heights were determined by µ-CT measurements and morphological tissue changes were histologically examined.Histological investigations show that, after treatment with the ASC-loaded collagen hydrogel implant, degeneration-specific features were observed less frequently. Quantitative studies of the degree of degeneration did not demonstrate a significant influence on potential tissue regeneration with treatment. Regarding disc height analysis, at both 6 and 12 months after treatment with the ASC-loaded collagen hydrogel implant a stabilization of the disc height can be seen. A complete restoration of the intervertebral disc heights however could not be achieved.The reported injection procedure describes in a preclinical model a translational therapeutic approach for degenerative disc diseases based on adipose-derived stem cells in a collagen hydrogel scaffold. Further investigations are planned with the use of a different injectable scaffold material using the same test model.
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Tao, Youping, Fabio Galbusera, Frank Niemeyer, René Jonas, Dino Samartzis, Daniel Vogele, and Hans-Joachim Wilke. "The impact of age, sex, disc height loss and T1 slope on the upper and lower cervical lordosis: a large-scale radiologic study." European Spine Journal 30, no. 9 (July 30, 2021): 2434–42. http://dx.doi.org/10.1007/s00586-021-06933-x.
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Abstract Purpose To clarify the relative influence of age, sex, disc height loss and T1 slope on upper (Occiput-C2) and lower cervical lordosis (C2–C7). Methods Standing lateral cervical radiographs of 865 adult subjects were evaluated. The presence and severity of disc height loss from C2/C3 to C6/C7 (a total of 4325 discs) were assessed using a validated grading system. The total disc height loss score for each subject was calculated as the sum of the score of each disc space. Sagittal radiographic parameters included: occipital slope, occiput-C2 (Oc-C2) lordosis, C2–C7 lordosis and T1 slope. Multivariable regression analyses were performed to examine the relative influence of the multiple factors on upper and lower cervical lordosis. Results This study included 360 males and 505 females, with a mean age of 40.2 ± 16.0 years (range, 20–95 years). Linear multivariate regression analyses showed that greater age, male sex, greater T1 slope were each found to be significantly and independently associated with greater C2–C7 lordosis, whereas total disc height loss score was negatively associated with C2–C7 lordosis. T1 slope had the most independent influence on C2–C7 lordosis among these factors. Age, sex and disc height loss were not independently associated with Oc-C2 lordosis. Conclusions Results from our large-scale radiologic analysis may enhance the understanding of the factors that affect cervical lordosis, indicating that age, sex, disc height loss and T1 slope were each independently associated with C2–C7 lordosis. However, age, sex and disc height loss were not independently associated with upper cervical lordosis.
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Sloan, Stephen, Christoph Wipplinger, Sirtac Kirnaz, Rodrigo Navarro-Ramirez, Antonella Schivinato, Roger Härtl, and Lawrence Bonassar. "3013 Combined Annulus Fibrosus and Nucleus Pulposus Repair Prevents Degeneration in the Ovine Lumbar Spine." Journal of Clinical and Translational Science 3, s1 (March 2019): 6. http://dx.doi.org/10.1017/cts.2019.17.
Full textAbstract:
OBJECTIVES/SPECIFIC AIMS: The objective of this study is to assess the efficacy of combined AF and NP repairs to prevent degenerative changes and restore native disc morphology in an in vivo large animal model. We hypothesize that combined repairs will prevent disc degeneration following injury to a greater extent than the individual repairs after 6 weeks in vivo, as demonstrated through disc height measurements and disc morphology. METHODS/STUDY POPULATION: A total of 8 skeletally mature female Finn sheep were used in this study. Following a previously described method, IVDs from L1 to L6 of the lumbar spine were exposed using a lateral access, extraperitoneal approach5. IVDs were randomized into 5 treatment groups: 1) intact discs, 2) discs injured via a 3 cm x 1 cm box annulotomy and partial nucleotomy, 3) injury followed by a high density collagen (HDC) AF patch, 4) injury followed by injection of a modified hyaluronic acid (HA) into the NP, and 5) injury followed by both the HDC AF patch and HA NP injection. The HDC treatment was 15 mg/mL type-I collagen mixed with 0.06mM riboflavin, injected at the defect site and crosslinked in situ with blue light. The NP injection was HA modified with C16 side chains to increase the viscosity of the hydrogel (HYADD 4®)6. At 6 weeks post-operatively, sheep were sacrificed and had 3T magnetic resonance images (MRI) taken of their lumbar spine. Disc height analysis and Pfirrmann grading were performed on each segment using MR images. Additionally, quantitative MRI analyses were performed using a custom MATLAB algorithm that segments NP from the surrounding tissue and directly measures the NP volume. ANOVA with Tukey’s HSD was used to determine statistical significance between groups for disc height and quantitative MRI analyses, and the Kruskal-Wallis test with Mann-Whitney tests was used to statistically analyze Pfirrmann Grades. All animal use followed approved IACUC protocol. RESULTS/ANTICIPATED RESULTS: As shown in axial MR images (Figure 1A), intact discs had hyperintense NP with a distinct border to the AF. The discs receiving injury with no treatment had hypointense NP with no distinct border between the AF and NP. Individual and combined treatment with the HA NP injection and HDC AF patch appeared to preserve the hyperintense NP signal and AF/NP border. Intact control discs were not degenerated and had an average Pfirrmann grade of 1 (Figure 1B), while injured, untreated discs had significant degeneration with an average Pfirrmann grade of 3. Discs receiving the HA NP injection and collagen AF patch individually showed fewer signs of degeneration than the injured alone, and the combined treatment resulted in the least amount of degeneration with Pfirrmann grades not significantly different than the intact controls. Disc height index confirmed the trends seen in the Pfirrmann grades (Figure 1C), where injured discs lost 20% of the intact disc height, the individual NP and AF repairs restored 5-10% of intact disc height, and the combined repairs preserved 90% of the intact disc height. The NP voxel count of all treatment groups were similar to the intact controls (Figure 1D). DISCUSSION/SIGNIFICANCE OF IMPACT: The objective of this study was to determine how combined AF and NP can prevent degenerative changes to the disc in a large animal in vivo model. Pfirrmann grading and disc height index results show that the greatest preservation of disc morphology was seen with combined AF and NP repairs, while the individual strategies prevented degenerative changes better than injury with no treatment. It appears the HA NP injection restores lost water content to the disc following injury, and the AF collagen patch plays a role in maintaining the NP repair within the disc. This is the first study to our knowledge to attempt combined AF and NP repairs in an in vivo large animal model. Combining NP and AF repairs leads to significantly improved outcomes following disc injury, which warrants the translation of combined repairs into the clinic to improve patient outcomes with degenerative disc disease involving NP and AF.
Dissertations / Theses on the topic "Disc height"
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Lally, Sarah Joanne. "pH-responsive hydrogel composites containing microgels : restoring intervertebral disc height through polymer composition." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/phresponsive-hydrogel-composites-containing-microgels-restoring-intervertebral-disc-height-through-polymer-composition(594cac41-952a-46a5-bad6-632d32cad3b1).html.
Full textAbstract:
This thesis presents a study into the use of microgels to restore degenerated intervertebral discs (IVDs). This was undertaken using a pH-triggered microgel which was able to form self-supporting gels through an increase in pH. The microgels were based on the poly(A/MAA/X) formulation, where MAA is methacrylic acid and A is the structural and X is the crosslinking monomer. The microgel particles were also used to construct composite poly(ethylene glycol) dimethacrylate (PEGD) hydrogels. The properties of the microgels and the composite hydrogels were then investigated. Microgel particles were synthesised based on poly(EA/MAA/BDD) (poly(ethyl acrylate/MAA/butanediol diacrylate). These were able to swell on increasing pH. Concentrated dispersions formed a gel with a high elastic modulus. The EA and BDD were replaced with related monomers and gave gels with different properties. Using monomers with high glass transition temperatures reduced the rate of swelling, and using monomers with similar reactivity ratios appeared to produce more uniformly crosslinked particles. It is proposed from the data presented that those with a large difference in reactivity ratio resulted in microgel particles with a change in crosslinking gradient through the radius of the particle. In some cases this produced microgels which appeared to fragment on increasing pH. The microgels investigated were based on poly(EA/MAA/X), (E-X) with BDD, EGD (ethylene glycol dimethacrylate) and PEGD. The EGD and PEGD microgels were shown to fragment with increasing pH. Poly(EA/MAA/PEGD) dispersions were able to form a gel at a pH below the pKa which appeared to be an electrostatically repulsive gel. Following this work, it became apparent that the E-BDD microgel was the most ideal of all the microgels with gels giving low values tanδ and frequency dependence of tanδ (tanδ = G"/G', where G" is the viscous modulus and G' is the elastic modulus). It also appeared to give physical gels with the highest elastic modulus. This microgel was therefore used for the composite gels. The poly(EA/MAA/BDD) microgel was then used to form covalently-linked composite hydrogels with PEGD of different molecular weights. PEGD with a molecular weight less than 550 formed a hydrogel-linked microgel, with interpenetrating polymer chains. These composites had high G' values and swelling ratios. Using PEGD with molecular weights higher than 550 produced microgel-filled hydrogels which had high values for G' and swelling ratios. Furthermore, due to osmotic deswelling of the microgel particles, the dispersions underwent a gel-to-fluid transition prior to being heated with initiator and crosslinked. This meant that some of the formulations were injectable. The mixture of high molecular weight PEGD and microgel was therefore combined with an accelerator which enabled gel formation and crosslinking at physiological temperature. Composites formed under physiological conditions were then tested for their ability to support biomechanically meaningful loads using degenerated IVDs. The discs were then compressed and the compressive strain to measured. The results showed that the composite was able to restore the mechanical modulus and height of the degenerated disc, showing favourable results for future research.
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Tez, Burkay Yasar. "Effects Of Specimen Height And Loading Span On The Fracture Toughness Of Disc Type Rock Specimens Under Three Point Bending." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609496/index.pdf.
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A relatively new fracture toughness testing method called Straight Notched Disc Bending (SNDB) was used before for fracture testing of Ankara Andesite and Afyon Marble cores. In this work to investigate the applicability of the new method to other rock types. With a preliminary notch of 10 mm, straight notched disc type specimens with a diameter of 75 mm were loaded by three-point bending loads.
Investigation of effect of specimen height on the stress intensity factor and fracture toughness was carried out. Specimen heights (B) between 18 &ndash67 mm were tried for andesite and marble cylindrical specimens. Loading span, that is span/radius (S/R) ratio was changed between 0.6 - 0.9 for andesite specimens. Stress intensity factor for specimens was computed with ABAQUS program. Stress intensity factor was found to increase with increasing specimen diameter for a fixed span/radius ratio. Stress intensity factor decreased with increasing specimen height. Changing span was found to have no significant effect on fracture toughness of andesite. Fracture toughness was significantly lower for specimens with smaller height. The suggested testing height interval for this type of specimens was between height/diameter ratios of 0.49 &ndash
0.64. Results were compared to the results obtained by a well-known specimen geometry named semi-circular bend specimens (SCB) under three-point bending. SCB tests produced lower values for fracture toughness for both rock types. Fracture toughness was 0.99 MPa&
#8730
m for Ankara Andesite and 0.70 MPa&
#8730
m for Afyon Marble.
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Liu, Xinqun. "Development of improved head-disk spacing measurement methods for magnetic disk drives." Thesis, University of Plymouth, 2002. http://hdl.handle.net/10026.1/2830.
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A detailed review of existing flying height or head disk spacing testing techniques has been made, and in-depth analyses of the working principles of the currently popular optical interferometry flying height testing methods are presented with simulation results. A new dual-beam normal incidence polarisation inteferometry method is then proposed. One advantage of this dual-beam polarisation interferometry is that it can be used for both the direct spacing measurement (DSM) method and relative displacement measuring (RDM) method. The RDM method is a good way to measure the head-disk spacing and the slider pitch or roll when a real magnetic disk is used for testing. The DSM method has the advantage that the absolute head-disk spacing can be observed and measured directly, especially in the case where it is difficult for the light beam to 'spot' the back surface of the head-slider. When used for the DSM method, the flying height can be measured down to contact without losing sensitivity. Slider pitch or roll can also be measured using the phase information. Another advantage of this polarisation interferometry is that, when used for the DSM method, with the measured intensity and phase information, the optical constants of the slider material can be determined, which is necessary to determine the flying height. By investigation of the application limits and potential problems of the intensity interferometry method, an improved intensity interferometry method is also proposed by using phase-shifting technique to improve the sensitivity of this method when the head-disk spacing is below 10 nm and near contact. An experimental testing system has been built to test the capability and effectiveness of the proposed interferometry methods. Experimental results are presented which show good agreement with the results gained from theoretical analyses and simulation.
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Chilumbu, Chibesa. "The development of a novel suspension arm with 2-dimensional actuation, for use in advanced hard disk drives." Thesis, University of Plymouth, 2002. http://hdl.handle.net/10026.1/1626.
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As magnetic computer disks are developed to ever-greater data storage densities, the accuracy required for head positioning is moving beyond the accuracy provided by present technology using single-stage voice-coil motors in hard disk drives. This thesis details work to develop a novel active suspension arm with 2-dimensional actuation for use in advanced hard disk drives. The arm developed is capable of high-bandwidth data tracking as well as precision head flying height control motion. High-bandwidth data tracking is facilitated by the use of piezoelectric stack actuator, positioned closer to the head. The suspension arm is also capable of motion in the orthogonal axis. This motion represents active flying height control to maintain the correct altitude during drive operation. To characterise the suspension arm's structural dynamics, a high-resolution measurement system based on the optical beam deflection technique has been developed. This has enabled the accurate measurement of minute end-deflections of the suspension arm in 2-dimensions, to sub-nanometre resolution above noise. The design process of the suspension arm has led into the development of novel piezoelectric-actuated arms. In the work involving lead zirconate titanate (PZT) thick films as actuators, work in this thesis shows that reinforcing the films with fibre improves the overall actuation characteristics of the thick films. This discovery benefits applications such as structural health monitoring. The final suspension arm design has been adopted because it is simple in design, easier to integrate within current hard disk drive environment and easier to fabricate in mass. Closed-loop control algorithms based on proportional, integral and derivative (PID) controller techniques have been developed and implemented to demonstrate high bandwidths that have been achieved. The suspension arm developed presents an important solution in head-positioning technology in that it offers much higher bandwidths for data tracking and flying height control; both very essential in achieving even higher data storage densities on magnetic disks at much reduced head flying heights, compared to those in existing hard disk drives.
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Han, Younghee. "A NEW PIEZOELECTRIC MICROACTUATOR WITH TRANSVERSE AND LATERAL CONTROL OF HEAD POSITIONING SYSTEMS FOR HIGH DENSITY HARD DISK DRIVES." UKnowledge, 2005. http://uknowledge.uky.edu/gradschool_theses/349.
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In high density magnetic hard disk drives, both fast track seeking and extremely accurate positioning of the read/write head are required. A new piezoelectric microactuator with transverse and lateral control of the head positioning system for high density hard disk drives is proposed. First, the structure of the new piezoelectric microactuator is illustrated. Design of the new microactuator is based on the axial deformation of piezoelectric elements for lateral motion and the bimorph actuation of piezoelectric elements for transverse motion. Next, a mathematical model of the microactuator system is defined. Static properties associated with the displacement of the system are evaluated and then dynamic system equations of the system are evaluated. Frequency response of the system is studied based on the dynamic system equations of the actuator system. Dynamic properties of the system with a variety of system parameters are evaluated. Finally, the controller design for the actuator is presented. Simulation results show that the new actuator achieves a maximum stroke of displacement of more than 0.2m with servo bandwidth of more than 5 kHz in the lateral direction and the flying height is decreased to less than 6 nm with resonance frequency of more than 100 kHz under the 0.5 % damping assumption. The new piezoelectric microactuator improves performance of high density hard disk drives by increasing servo bandwidth and decreasing flying height.
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Moti, Farah Razack. "Clinical method of calculating optic nerve head vertical disc height." Thesis, 2014.
Find full textAbstract:
There is large variability between individuals on many measurable
parameters of the optic disc. The retinal fundus is most commonly measured indirectly
via slit-lamp biomicroscopic examination with a fundus spherical lens.
Three optical methods of measuring the vertical disc height were compared:
– Optical Coherence Tomographic (OCT) method
– Calculation using a modified Littman’s equation: t = pqs
– Measurement using five different double aspheric Volk fundus lenses on two
different slit lamps (Haag-Streit and CSO)
The aims of the study were:
– To calculate a conversion equation of optic disc height measurement by clinical
assessment using any one of five double aspheric fundus lenses at the slit-lamp
– To compare the control mechanism of optic disc height measurement on OCT
versus calculation using a modified Littman’s equation
– To compare measurements between the Haag-Streit BM900 and CSO SL990 slit
lamps
– To compare accuracy and agreement of Volk conversion factors based on
manufacturer magnification values to the control mechanism
DESIGN & METHOD: A cross-sectional study was performed on patients presenting to
the St John Eye Hospital from August ’11 to July ‘12. 100 eyes were measured for:
– The optic nerve head vertical disc height on OCT
– Vertical disc height (VDH) on Haag-Streit and CSO slit lamps with Volk super 66D,
78D, Superfield, Digital Wide Field, Digital High Magnification lenses
– Axial length
– Refraction
Subsequently, 44 new eyes were measured and used to test agreement of the
formulated equations.
RESULTS:
– Axial length was not found to have a correlation with VDH (p=0.64).
– The modified Littman’s equation: t=pqs where p varies for each lens and q =
0.01306(axial length – 1.82), had very low correlation and poor agreement
– Comparing formulated equations to the OCT VDH, the formulated Digital High
Magnification and super 66D lenses were found to have the most accuracy
– Measurements with the Volk Digital Wide Field lens were highly inaccurate and are
therefore not recommended for vertical disc height measurement in future
– Comparison of the fundus lens measurements using the two slit lamps showed
alarmingly different results. There was no agreement between slit lamp
measurements using four of the lenses
CONCLUSIONS:
– The use of axial length and other quantitative factors attained by measures of a
schematic eye cannot be used accurately in clinical practice to determine fundus
object sizes.
– The slit lamp technique of measuring optic disc size with application of a simple
equation yields useful results in close agreement to those yielded by expensive
technology. It cannot replace accurate analysis using an OCT but is sufficient in aiding
clinical decisions
– Two important factors need to be taken into account when applying slit lamp fundus
measurements: the type of lens used, and the slit lamp being used – as measurement
standards are inconsistent between slip lamps
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Liou, Bing-Hung, and 劉炳宏. "Design and Control of Micro-Magnetic Height Adjuster for Rotating Disc." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/58968805606490756435.
Full textAbstract:
碩士國立成功大學
機械工程學系碩博士班
97
An innovative magnetic module which is concurrently capable of performing as an actuator and a sensor is proposed and illustrated. The magnetic module is basically similar to a micro-scale solenoid coil which is employed to actively adjust the height of a seismic rotating disc used in a gyroscope so that the induced pitch angle by Coriolis effect, purely due to exerted angular excitation, can be accurately measured. That is, the micro-magnetic module acts like an actuator for height regulation on the seismic rotating disc by applying appropriate electric current to the primary coil of the Micro-Magnetic Height Adjuster (MMHA). On the other hand, the secondary coil pair of the MMHA acts as a sensor which can detect the gap change between the seismic rotating disc doped by metal material, and the micro-magnetic module.
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PAN, LONG JYH, and 潘隆智. "The control in flying height of slider in hard disk." Thesis, 1993. http://ndltd.ncl.edu.tw/handle/26284954754794523710.
Full textAbstract:
碩士國立臺灣大學
機械工程研究所
81
This research addresses the problem of the read/write head fly height control in a computer hard disk drive. The computer hard disk read/write head flies above the disk at a very small distance in order to pick up small magnetization changes on the recording surface. The distance between the head and the disk thus determines the available recording density of the media. Modern computer disk drive achieves minimum fly height by using the air-bearing technology without feedback control. The air- bearing is able to maintain the read/write head at a sub-micron distance above the disk surface. As the need for storage capacity increases, it is necessary to futher reduce the fly height, and certain form of feedback control becomes necessary. In this research, we develop a mean to measure the read/write head fly height in a commercially available hard disk drive. In order to perform controller design, we also develop a system model that includes both the slider dynamics and the air- bearing squeeze effect. The popular $H_\infty$ optimization procedure is then used for controller synthesis. Experimental results on the fly height measurement and simulation results on the fly height control confirm the feasibility of the approach.
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Tzeng, Shih-Che, and 曾士哲. "The CSS Performance of Low Glide Height Head-Disk Interface for High-Performance Disk Drives." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/19909587536929919358.
Full textAbstract:
碩士元智大學
機械工程學系
91
The present objective of the research is to get the high density recording system. However, a higher recording density requires smaller head-disk spacing, and therefore lowering-flying heads and smoother disk surfaces are needed. Due to the lowered fly height of the slider, glide avalanche requirements of the disks are consequently being tightened while the stiction requirement remain unchanged. In this article, the limitations of padded slider to meet stiction requirement on low glide height media tribology issue were investigate. In order to meet the glide avalanche requirement, to change the laser energy and its size of the laser texturing machine to get a concaved laser bump geometry, it can be seen that such design can get lower glide height but higher stiction. Therefore , to get the optimal design of such head/disk interface to get lower stiction is necessary. In the research, we observed that smaller bump spacing, bigger bump diameter, lower concave depth and fewer lubricant apply can reduce the contact area and meniscus of the head/disk interface, and exhibits better CSS performance in the test. In terms of the stiction model, it can be seen that more uniform asperity height distribution and lower lubricant tensor can get lower stiction force., Hence the better understood CSS technology is expected to be further extended into future high-performance disk drives.
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劉育銘. "The disk/head flying height variation measured by laser doppler vibrometer." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/68989911689403669023.
Full textBook chapters on the topic "Disc height"
1
Cuisinier, F., A. Acker, and J. Köppen. "Dependance of the Metallicity of Planetary Nebulae with the Galactic Height above the Disk." In Planetary Nebulae, 578. Dordrecht: Springer Netherlands, 1993. http://dx.doi.org/10.1007/978-94-011-2088-3_262.
Full text
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Shi, B. J., D. W. Shu, B. Gu, M. R. Parlapalli, C. N. Delia, and Q. Y. Ng. "Air Bearing Slider Simulation and Modeling for Hard Disk Drives with Ultra-Low Flying Heights." In Computational Mechanics, 314. Berlin, Heidelberg: Springer Berlin Heidelberg, 2007. http://dx.doi.org/10.1007/978-3-540-75999-7_114.
Full text
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Miller, Allison N., Mark Powell, and Arunima Ray. "Tower Height Raising and Embedding." In The Disc Embedding Theorem, 253–70. Oxford University Press, 2021. http://dx.doi.org/10.1093/oso/9780198841319.003.0018.
Full textAbstract:
‘Tower Height Raising and Embedding’ shows how to raise the height of towers, as well as how to detect embedded towers within a given tower. Raising the number of storeys of a capped tower by one is a construction similar in spirit to grope height raising, but more sophisticated. The new aspect, which receives careful treatment, is the geometric control needed to make the top storey arbitrarily small. An n-storey capped tower contains a capped tower with (n + 1) storeys and the same attaching region, and this can be realized by an embedding that places connected components of the top storey into balls of arbitrarily chosen small diameter. Consequently, endpoint compactifications of infinite towers may be embedded as well.
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Kim, Min Hoon, Patrick Orson, JungHwan Park, and Arunima Ray. "Good Groups." In The Disc Embedding Theorem, 273–82. Oxford University Press, 2021. http://dx.doi.org/10.1093/oso/9780198841319.003.0019.
Full textAbstract:
Good groups are defined in terms of whether capped gropes of height 1.5 contain certain types of immersed discs. The disc embedding theorem holds for 4-manifolds with good fundamental group. It is proven that the infinite cyclic group and finite groups are good, and that extensions and colimits of good groups are good. This shows that all elementary amenable groups are good. The proofs use grope height raising and contraction, together with an analysis of how fundamental group elements behave under these operations. A central open problem in the study of topological 4-manifolds is to determine precisely which groups are good.
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Feller, Peter, Mark Powell, and Arunima Ray. "Grope Height Raising and 1-storey Capped Towers." In The Disc Embedding Theorem, 239–52. Oxford University Press, 2021. http://dx.doi.org/10.1093/oso/9780198841319.003.0017.
Full textAbstract:
‘Grope Height Raising and 1-Storey Capped Towers’ upgrades the capped gropes constructed in the previous chapter to 1-storey capped towers. Grope height raising is a technique that shows that every capped grope of height at least 1.5 can be improved to a capped grope of arbitrary height. The technique is explained in this chapter in detail, and used multiple times in the rest of the proof. The chapter closes by showing how to extend capped gropes to 1-storey capped towers. This crucially uses the hypothesis that the fundamental group is good. It is the single place in the proof of the disc embedding theorem that requires this hypothesis.
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Kotwicki, T., S. Rubczak, and P. Glowka. "Three-dimensional reconstruction of intervertebral disc based on magnetic resonance imaging in patients with acute low back pain." In Studies in Health Technology and Informatics. IOS Press, 2021. http://dx.doi.org/10.3233/shti210436.
Full textAbstract:
The aim of the study is to evaluate the morphology of the intervertebral discs visible in the magnetic resonance image in patients with sudden severe low back pain (with or without radiation of pain to the lower limb). The second goal of the study is to perform a digital three-plane reconstruction of the intervertebral disc and to compare this technique with a standard magnetic resonance imaging test. Twenty-five patients, mean age 35.5 years, all with acute low back pain, were examined. We compared the 3D MR models with standard MRI scans by measuring seven MRI parameters. In patients with sudden, severe low back pain, with clinical symptoms suggesting an etiology within the intervertebral disc, changes in a standard MRI are found consisting of the presence of a hernia / protrusion of the intervertebral disc and lowering the height of the intervertebral disc – with lowering the disc height occurs to a greater extent in the rear section. The 3D reconstruction is a reliable 3D representation of the intervertebral disc and adjacent vertebral bodies.
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Yeung, KH, GCW Man, ALH Hung, TP Lam, JCY Cheng, and WCW Chu. "Morphological changes of intervertebral disc in relation with curve severity of patients with Adolescent Idiopathic Scoliosis – a T2-weighted MRI study." In Studies in Health Technology and Informatics. IOS Press, 2021. http://dx.doi.org/10.3233/shti210431.
Full textAbstract:
The purpose of this study was to evaluate the morphological changes of intervertebral discs (IVD) and vertebral bodies (VB) in AIS girls according to the subgroups with different curve severity by magnetic resonance imaging (MRI). This study included 33 age-matched female controls and 76 AIS girls with a right-sided thoracic curvature. Wedge angle, height ratio and distance ratio of VB and IVD were measured on the best midline coronal and sagittal planes from reformatted MRI spine. Volumes of VB, IVD and nucleus pulposus (NP) were evaluated on volumetric images. One-way ANOVA with Bonferroni correction was used. There was significant difference in wedge angle and height ratio of VB and IVD between AIS and controls. In severe-AIS, the position of NP was significantly shifted to the convexity when compared with non-severe AIS and controls. Whereas, the volume of IVD and NP in severe-AIS was found to be significantly smaller. On top of coronal wedging of VB and IVD, there was significantly reduced volume of IVD and NP in severe-AIS patients, despite T2 signal of IVD was preserved. The current findings indicate that early mechanical effects on the discs and vertebrae in adolescent scoliotic spine is evident on quantitative imaging. Importantly, these patients may be vulnerable to disc degeneration if no operative treatment is prescribed.
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Hoover, Kevin B., and Tim B. Hunter. "Spinal Fixation Hardware." In Musculoskeletal Imaging Volume 1, edited by Kevin B. Hoover, 224–30. Oxford University Press, 2019. http://dx.doi.org/10.1093/med/9780190938161.003.0049.
Full textAbstract:
Chapter 49 discusses spinal fixation hardware. The spine is the primary structural support of the human body. Traumatic, neoplastic, infectious, or degenerative disruption of the 3 columns of the spine causing pain and instability are the primary indications for spine surgery. Implanted hardware is used to provide short-term stability while osseous fusion of bone graft develops. Radiographs are routinely used for pre- and postoperative evaluation. Spinal fusion is used to restore and maintain disc space height, to decompress the spinal canal and neural foramina, to maintain normal lordosis, and to increase the stability of involved segments. Cross-sectional imaging is important for identified hardware and soft tissue complications.
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Woodruff, Todd E. "Optic Nerve Examination." In Glaucoma. Oxford University Press, 2012. http://dx.doi.org/10.1093/oso/9780199757084.003.0009.
Full textAbstract:
•Small field of view but increased magnification •Significant degradation of the view from media opacities or small pupil •Lacks ability to perform stereoscopic examination •Useful when slit-lamp exam not possible •Most commonly used system •Variable magnification and field of view • Reasonable view through small pupil • Good stereoscopic view •Less degradation of view from media opacities than direct ophthalmoscope •The magnification and stereopsis obtained with a slit-lamp system is generally superior to that of a handheld or headlamp-based system. • Poor magnification, with wide field of view •Least degradation of view from media opacities •Value of stereopsis limited by poor magnification Fair to poor with small pupils •May be useful for bedside exam or in the operating room • The vertical diameter of the optic nerve can be easily estimated during a slit-lamp exam by the following method: 1. A thin slit beam is focused on the nerve through the lens of choice. 2. The vertical length of the beam is adjusted to match the height of the disc. 3. The length of the beam is read off the slit-lamp beam scale. 4. The scale reading is adjusted by the correction factor of the specific lens. •This estimation is reasonably accurate, but it tends to underestimate disc size in high levels of myopia, and overestimate in high hyperopia. • One can also use the scale projection of the direct ophthalmoscope to estimate nerve head size, with no correction factor needed. The small light cone of the direct ophthalmoscope subtends an angle of about 5 degrees, about the same size as an average optic disc, and can give a quick estimate of relative size. • Stereo-photographs are the most helpful but are more difficult to obtain in a reproducible manner. •Cameras with a prism-based fixed-angle method of taking simultaneous stereo-photos tend to produce more consistent results, but are more expensive. • While non-mydriatic cameras exist, images suffer when the pupil is smaller than 4 mm, and dilation is commonly employed to obtain the best images.
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Wu, S., and Y. J. Liu. "Experimental Study on Operation Performance of Two-Body Wave Energy Generator." In Advances in Transdisciplinary Engineering. IOS Press, 2021. http://dx.doi.org/10.3233/atde210282.
Full textAbstract:
The two-body oscillating type wave energy converter (WEC) is a hot research topic at present. A two-body device with damping disc was taken as the test model in this paper. The two bodies were connected by a hydraulic piston cylinder to realize the relative motion energy conversion. Physical experiments were carried out in a wave-making flume to study the operation performance. The effects of wave elements and load on the hydrodynamic characteristics and capture width ratio (CWR) of the model were analysed respectively. The results showed that wave frequency and external load were the main factors affecting the motion response and energy conversion of the device. With the increase of wave frequency and external load, the response amplitude operator (RAO) and the capture width ratio both increase first and then decrease. Wave height has little effect on system characteristics. There exists a best-matching wave period condition, and the optimal motion response and energy conversion are obtained.
Conference papers on the topic "Disc height"
1
Kim, Jesse G., Tae-Hong Lim, Susan M. Renner, Atsushi Fujiwara, Cahn Nuyen, Taekhoon Yoon, and Howard S. An. "Experimental Intervertebral Disc Degeneration: Compressive Behavior Changes Over Time." In ASME 2000 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2000. http://dx.doi.org/10.1115/imece2000-2611.
Full textAbstract:
Abstract Changes in axial compressive behavior of the intervertebral disc resulting from annulus stab wound were investigated using rabbit discs. Results of this study clearly showed that stabbing incision could cause disc degeneration with losses in disc height, elastic modulus, and energy dissipation capacity in 8 weeks after injury. Disc specimens obtained at 12 weeks after stab incision showed no further changes in disc height and axial compressive behavior from those found in 8 week specimens.
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Anderst, William J., Thomas P. Lacek, William F. Donaldson, Joon Y. Lee, and James D. Kang. "Cervical Disc Height During Dynamic In Vivo Flexion-Extension." In ASME 2011 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2011. http://dx.doi.org/10.1115/sbc2011-53154.
Full textAbstract:
Cervical disc degeneration is a common and potentially debilitating disease. Over 100,000 surgical procedures are performed per year in the US to treat degenerative cervical spines1. However, the in vivo kinematics and arthrokinematics of the cervical spine have yet to be adequately characterized due to the inability to precisely track vertebral movement during dynamic motion. We have recently established the validity of a set of tools, including a biplane x-ray system, a model-based tracking technique and custom software, to precisely measure in vivo cervical spine kinematics and arthrokinematics with sub-millimeter accuracy2. Consequently, we can now begin to investigate the interdependent relationship between cervical vertebral kinematics and disc morphology and mechanical properties.
3
Bhansali, Pratik S., and Srinath V. Ekkad. "Effect of Variation of Pin-fin Height on Jet Impingement Heat Transfer on a Rotating Surface." In ASME 2021 Heat Transfer Summer Conference collocated with the ASME 2021 15th International Conference on Energy Sustainability. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/ht2021-63946.
Full textAbstract:
Abstract Heat transfer over rotating surfaces is of particular interest in rotating machinery such as gas turbine engines. The rotation of the gas turbine disc creates a radially outward flow on the disc surface, which may lead to ingress of hot gases into the narrow cavity between the disc and the stator. Impingement of cooling jet is an effective way of cooling the disc and countering the ingress of the hot gases. Present study focusses on investigating the effect of introducing pin-fins over the rotating disc on the heat transfer. The jet Reynolds number has been varied from 5000 to 18000, and the rotating Reynolds number has been varied from 5487 to 12803 for an aluminum disc of thickness 6.35mm and diameter 10.16 cm, over which square pins have been arranged in an inline fashion. Steady state temperature measurements have been taken using thermocouples embedded in the disc close to the target surface, and area average Nusselt number has been calculated. The effects of varying the height of the pin-fins, distance between nozzle and the disc surface and the inclination of the impinging jet with the axis of rotation have also been studied. The results have been compared with those for a smooth aluminum disc of equal dimensions and without any pin-fins. The average Nusselt number is significantly enhanced by the presence of pin fins. In the impingement dominant regime, where the effect of disc rotation is minimal for a smooth disc, the heat transfer increases with rotational speed in case of pin fins. The effect of inclination angle of the impinging jet is insignificant in the range explored in this paper (0° to 20°).
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Jia, Xingyun, Qun Zheng, Hai Zhang, and Yuting Jiang. "Effects of Rotor Disc Growth on Flow and Heat Transfer Characteristics of Rim Seal." In ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/gt2017-64169.
Full textAbstract:
Under actual operating conditions of gas turbine, centrifugal and thermal growth of disc in radial direction result in dislocation of inflow boundary at the disc mid-radius height, and a radial step of platform at high radius height. In this paper, flow and heat transfer characteristics in dislocated rim seal region are analyzed by the conjugate and thermal mechanical numerical methods. The calculated radial growths of turbine discs reach approximately 14–20 % of turbine platform structure thickness. Dislocation of rim seal structure directly affects the flow characteristic of externally-induced (EI) ingress and rotationally-induced (RI) ingress, and aggravates overheat of stator disc due to induced hot gas ingestion, further affects the loss of mixture of mainstream gas and cooling sealant air flow in rim-seal and wheelspace regions. Radial step between rotor and stator platforms exacerbates the area and depth of hot gas ingestion in seal clearance, along with a 2–7 % decrease in seal efficiency.
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Showalter, Brent L., Ian S. MacLean, Dawn M. Elliott, and Neil R. Malhotra. "Nucleotomy Alters Mechanical Function Following Cyclic Loading and Unloaded Recovery of Human Discs." In ASME 2012 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/sbc2012-80487.
Full textAbstract:
The intervertebral disc plays a critical role in supporting loads, permitting spinal motion, and dissipating energy. Unfortunately, it is also commonly degenerated, resulting in altered spinal mechanics and low back pain. Nucleotomy is a common treatment for herniated discs and is also used experimentally to simulate degeneration.[1] The procedure, which involves a posterior annular incision and removal of a portion of the nucleus pulposus (NP), has also been shown to alter disc mechanics. These changes include acute changes of decreased NP pressure, decreased disc height, and increased neutral zones.[2, 3] Cyclic studies have shown that trans-endplate nucleotomy permanently alters creep mechanical properties of sheep discs.[4] However, the effects of annular nucleotomy on the cyclic properties of human discs have not yet been studied. This work studied the mechanical effect of annular nucleotomy on human discs subjected to physiological axial cyclic loading.
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Natarajan, Raghu N., Howard S. An, and Gunnar B. J. Andersson. "Geometric Changes in a Lumbar Disc Have a Greater Effect on Disc Biomechanics Than Changes in the Biomechanical Properties of the Disc." In ASME 2011 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2011. http://dx.doi.org/10.1115/sbc2011-53044.
Full textAbstract:
Structural alterations of the disc are accompanied by changes in disc tissue structure and composition during degeneration processes. As the lumbar disc degenerates, the disc height decreases. At the same time due to the development of fissures and cracks in the annulus, its material behavior changes. The degeneration process also includes cleft formation in the nucleus and reduction in water content in the nucleus. The clear demarcation between nucleus and surrounding annulus slowly disappear as the disc degeneration progresses thus increasing the annulus volume while reducing the nucleus volume. Both in-vitro and finite element studies exist in literature which deals with the biomechanical effect of disc degeneration. The changes in biomechanical behavior due to degeneration are a combined effect of change in geometrical parameters of the disc and change in material characteristics of the disc components. It is not known whether the change in disc geometries or the change in disc material properties has a predominant effect in altering the disc biomechanics. The current study focuses on this aspect.
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Kumaresan, Srirangam, Frank A. Pintar, Narayan Yoganandan, Phaladone J. Khouphongsy, and Joseph F. Cusick. "Intervertebral Disc Morphology in Cervical Spine Biomechanics." In ASME 1999 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/imece1999-0464.
Full textAbstract:
Abstract Although qualitative descriptions of degenerative changes in the intervertebral disc components have been reported, methods to quantify these changes are lacking. A methodology was developed in this study to quantify the three-dimensional geometrical variations of the annulus fibrosus and nucleus pulposus. Fresh isolated intervertebral discs with adjacent vertebral bodies of skeletally mature young and old adult primates were sectioned sequentially, and different staining methods were used to distinguish the annulus and nucleus. Histological images were examined using light microscopy and exported to a computer to trace the boundaries of the annulus fibrosus and nucleus pulposus. Dorsal to ventral depth, medial to lateral width, and caudal to cranial height measurements of the nucleus pulposus and its relative location to the annulus pulposus were obtained. In the young adult, the nucleus was translucent with scattered notochordal cells. In the older adult, the nucleus appeared as a dense region of amorphous, irregular collagen material. A higher geometrical variation of nucleus due to degeneration was noted in the sagittal plane compared to coronal plane. Determination of the three-dimensional geometrical variations and histology analyses will assist mathematical modelers to better define the disc to study the biomechanics of the cervical spine.
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Rüsenberg, Stefan, and Georg Vonnahme. "Failure Analysis of High Pressure Rupture Discs and Effective Counter Measures." In ASME 2016 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/pvp2016-63841.
Full textAbstract:
For the production of LDPE, high process pressures (>1000 bar up to 3500 bar and above) as well as high temperatures (>100 °C up to 300 °C and above) are required. In order to ensure a safe production process the autoclaves and compressors have to be protected against dangerous overpressure. Rupture discs are typically used to protect this high pressure process itself, as well as the employees, and the environment. Traditionally rupture discs for high pressure applications are manufactured by a weld seam which has an influence on the burst pressure. After installation the applied pressure is nearly fully-loaded on the welding joint. Additionally, the welding joint is another unwanted influencing factor. This increases the possibility of an unexpected failure which leads to an unwanted rupture disc response or, in critical cases, to a rupture disc failure recently after initial operation of the process even at lower pressures than the defined burst pressure. This, in turn, leads to a reduced life time of the disc. A special version of a rupture disc, a High Pressure Rupture Disc (HPRD) is developed specifically for this application. This long life version for high pressure applications has a lifetime which is 5–10 times higher than that of a standard rupture disc, that saves money and installation time. The differences are explained in some minor geometrical changes. This safety device allows a protection of high pressures up to 4000 bar and beyond. The HPRD is a forward acting rupture disc and the burst pressure is adjusted by a combination of material thickness, the height of the dome, and, of course, of the chosen material. An easy and simple geometrical change eliminates the welding joint as an influencing factor, thus eliminating any unwanted responding of the rupture disc. The tolerances for high pressure rupture discs are +/−3% and lower and the HPRD can be used for all kind of different high pressure applications.
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Arthur, Amy, Marco Cannella, Michael Keane, Wamis Singhatat, Ed Vresilovic, Sumona Sarkar, and Michele Marcolongo. "Fill of the Nucleus Cavity Affects Mechanical Stability in Compression, Bending and Torsion of a Spine Segment Which Has Undergone Nucleus Replacement." In ASME 2009 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2009. http://dx.doi.org/10.1115/sbc2009-206637.
Full textAbstract:
Axial loading, rotation and bending were applied to human cadaveric lumbar segments to investigate changes in disc mechanics with denucleation and incremental delivery of a novel hydrogel nucleus replacement implant. Changes in disc height, range of motion, neutral zone, hysteresis and stiffness were examined.
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Makwana, Anand R., A. R. Krishna, Hao Yuan, Reuben H. Kraft, Xianlian Zhou, Andrzei J. Przekwas, and Phillip Whitley. "Towards a Micromechanical Model of Intervertebral Disc Degeneration Under Cyclic Loading." In ASME 2014 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/imece2014-39174.
Full textAbstract:
A number of activities subject the spinal cord [1] to various loading conditions that lead to disc degeneration. In this paper a brief overview on the understanding of the micromechanics and mechanisms of intervertebral disc degeneration is presented and extended to include water loss and disc height change. The focus is on a computational model of the intervertebral disc degeneration that attempts to capture the initiation and the progression of the damage mechanism under fatigue. This model can be used to study the effects on disc under short or long period biomechanical loading in work or combat environments.