Unilateral Loading Research Articles

Inhibited cardiac hypertrophy in proadrenomedullin NH2-terminal 20 peptide-transgenic rat with unilateral nephrectomy and high salt loading

Proadrenomedullin NH2-Terminal 20 peptide (PAMP) is synthesized from the same preproadrenomedullin gene of adrenomedullin (AM). Unlike AM, little is known about PAMP. We developed transgenic rats by constructing a PAMP transgene incorporating the potent chicken β-actin promoter and then microinjected into fertilized eggs from superovulated Wistar rats. Potential transgenic founders were screened by PCR of genomic DNA from rat tail tips. Significant increase of human PAMP levels was confirmed in both plasma and tissues by ELISA method. PAMP-transgenic (Tg) or wild (W) rats were fed a high salt diet (8% NaCl) but with free access to drinking water for 5 weeks after unilateral nephrectomy. Rats were sacrificed and plasma and tissue were sampled at the end of 5 week. Rat heart tissue was either evaluated by immunohistochemistry or by real-time quantitative PCR methods for gene quantification. Heart rate did not significantly differ in two groups. However, systolic blood pressure, weekly measured by tail-cuff method, was attenuated in Tg rats compared with wild ones (p<0.05). Meanwhile, the cardiac hypertrophy in wild rat was significantly ameliorated in the Tg rat with heart weight (mg) to body weight (g) ratio of 3.5±0.1 to 2.99±0.11 (p<0.05). The cardiac fibrosis observed in wild rat was significantly attenuated by 50% in Tg rat (p<0.05). Further evaluation of the local renin-angiotensin system (RAS) related genes in the left ventricle by real-time PCR method showed that ACE gene transcription in Tg rat was downregulated to 60% of wild rat (p<0.05). Renin gene expression, however, was about 2.5-fold upregulated in Tg rat (p<0.05), reflecting the subsequently reduced angiotensin II production in the heart. This is also consistent with previous report that renin gene transcription is negatively regulated by angiotensin II. In contrast to local renin changes in heart, plasma renin activity was not significantly different in the two groups, though both were inhibited by salt loading. In conclussion, PAMP possesses hypotensive and anti-hypertrophy effect in this model implicating its clinical application of hypertension and organ damage.

Effects of Long-Term Tennis Playing on the Muscle-Bone Relationship in the Dominant and Nondominant Forearms

The relationship between muscle strength and bone mineral density illustrates the positive effect of mechanical loading on bone. But local and systemic factors may affect both muscle and bone tissues. This study investigated the effects of long-term tennis playing on the relationship between lean tissue mass and bone mineral content in the forearms, taking the body dimensions into account. Fifty-two tennis players (age 24.2 +/- 5.8 yrs, 16.2 +/- 6.1 yrs of practice) were recruited. Lean tissue mass (LTM), bone area, bone mineral content (BMC), and bone mineral density were measured at the forearms from a DXA whole-body scan. Grip strength was assessed with a dynamometer. A marked side-to-side difference (p < 0.0001) was found in favor of the dominant forearm in all parameters. Bone area and BMC correlated with grip strength on both sides (r = 0.81-0.84, p < 0.0001). The correlations were still significant after adjusting for whole-body BMC, body height, or forearm length. This result reinforced the putative role of the muscles in the mechanical loading on bones. In addition, forearm BMC adjusted to LTM or grip strength was higher on the dominant side, suggesting that tennis playing exerts a direct effect on bone.

Photoelastic analysis of the effect of palatal support on various implant-supported overdenture designs.

The effect of palatal support on various types of implant-supported maxillary overdenture designs has not been sufficiently assessed. The purpose of this study was to photoelastically evaluate the palatal support of 3 designs of maxillary implant-supported overdentures. A photoelastic model of an edentulous maxilla was fabricated with four 3.75 x 13-mm 3i implants. Three maxillary overdenture designs were fabricated: a splinted Hader bar incorporating 2 distal ERA attachments with anterior clips; non-splinted Zaag 4-mm direct abutments and attachments; and nonsplinted Locator 2-mm direct abutments and attachments. All restorative components and attachments were fitted and observed for passivity of fit and alignment. The overdentures were first tested with complete palatal coverage. Unilateral 25-lb loads were applied at the left and right first molars and the incisive papilla area. The photoelastic effects were monitored and recorded photographically. The palatal area was removed from the 3 overdentures and the loading regimens were repeated. The highest stresses under central loading were seen with the splinted Hader bar and complete palatal coverage, followed by similar levels of stress with either Zaag or Locator attachments. After removal of the palate, the center load demonstrated greater differences between designs. The highest stresses were observed with the Hader bar, followed by the Zaag and then Locator attachments. Lack of palatal coverage demonstrated higher levels of stress around implants and visible supporting tissues. The unilateral load produced the highest stress for the splinted Hader bar, followed by Locator, and then Zaag. Removal of the palatal support produced a greater effect and more concentrated stress difference for maxillary overdentures than differences between the attachment designs tested.

Photoelastic analysis of the effect of palatal support on various implant-supported overdenture designs

Statement of problem The effect of palatal support on various types of implant-supported maxillary overdenture designs has not been sufficiently assessed. Purpose The purpose of this study was to photoelastically evaluate the palatal support of 3 designs of maxillary implant-supported overdentures. Material and methods A photoelastic model of an edentulous maxilla was fabricated with four 3.75×13-mm 3i implants. Three maxillary overdenture designs were fabricated: a splinted Hader bar incorporating 2 distal ERA attachments with anterior clips; non-splinted Zaag 4-mm direct abutments and attachments; and nonsplinted Locator 2-mm direct abutments and attachments. All restorative components and attachments were fitted and observed for passivity of fit and alignment. The overdentures were first tested with complete palatal coverage. Unilateral 25-lb loads were applied at the left and right first molars and the incisive papilla area. The photoelastic effects were monitored and recorded photographically. The palatal area was removed from the 3 overdentures and the loading regimens were repeated. Results The highest stresses under central loading were seen with the splinted Hader bar and complete palatal coverage, followed by similar levels of stress with either Zaag or Locator attachments. After removal of the palate, the center load demonstrated greater differences between designs. The highest stresses were observed with the Hader bar, followed by the Zaag and then Locator attachments. Lack of palatal coverage demonstrated higher levels of stress around implants and visible supporting tissues. The unilateral load produced the highest stress for the splinted Hader bar, followed by Locator, and then Zaag. Conclusions Removal of the palatal support produced a greater effect and more concentrated stress difference for maxillary overdentures than differences between the attachment designs tested.

Long bone robusticity and subsistence behaviour among Later Stone Age foragers of the forest and fynbos biomes of South Africa

The robusticity of human long bone diaphyses can provide information about habitual behaviour among humans in the past. Mechanically relevant morphological variables include the strength of the diaphysis relative to body size, asymmetry between antimeres, diaphyseal shape, and sexual dimorphism in mechanical properties. This study compares the long bone robusticity of humeri, ulnae, femora and tibiae of Later Stone Age foragers from the forest and fynbos biomes of the southern African Cape region ( n=65:32m,33f), dated primarily to between 8000 and 2000 BP. Ecological differences between these biomes dictate variation in the terrestrial resource base, although marine contributions to diet are significant throughout the Cape. Female robusticity remains relatively homogenous between the forest and fynbos biomes, and is characterized by relative symmetry in strength characteristics between paired upper limb elements with antero-posteriorly strengthened diaphyses. This morphology is consistent with shellfish harvesting and the use of digging sticks throughout the Later Stone Age in these regions. Male lower limb robusticity is consistently high in both biomes, suggesting that high levels of terrestrial mobility were characteristic of male subsistence strategies. The forest biome males have higher levels of bilateral asymmetry in upper-limb robusticity than males of the fynbos biome. This morphology may correspond with increased unilateral loading resulting from a higher frequency of use of spear projectiles relative to bows and arrows, and greater exploitation of medium to large sized bovids.

Visualization of femorotibial contact in total knee arthroplasty using X-ray fluoroscopy

The purpose of this study was to build a visualization technique of the femorotibial contact in fixed-bearing total knee arthroplasty (TKA) using X-ray fluoroscopy, and to apply this technique to a TKA patient during dynamic motion. In vivo kinametcis of the metallic knee implant was determined using a 2D/3D registration technique, which uses computer assisted design (CAD) model of the implant to estimate the 3D pose of radiopaque metallic femoral and tibial components from a single-plane fluoroscopic image. In fixed-bearing TKA, a 3D pose of radiolucent tibial polyethylene insert can be determined from the estimated pose of the tibial component. To visualize femorotibial contact, the proximity between surfaces of femoral component and tibial insert was calculated, and mapped onto the insert surface model. For the clinical application, dynamic states of contact on the tibial insert were observed including axial rotation and unilateral loading during knee flexion, and post-cam contact of posterior stabilized TKA. The present technique provided us new information and enabled us to better understand the relationship between in vivo knee kinematics and articular shape of the implant.

Endommagement anisotrope du béton

Damage modelling exposed in this paper belongs to the anisotropic model class, its originality reside into the way adopted to treat unilateral aspects and loading path rotations. The model allows t...

ワイヤーエーカース鉤の舌面形態の違いが犬歯支台の挙動に及ぼす影響

On a case of distal extension removable partial prostheses with only six frontal teeth remaining, the wrought wire Akers clasp system has been usually used in expectation of the stress breaking action of flexible compornents because of an unfavorable prognosis. No plactical availability of this system, however, has been confirmed in vivo and in vitro too. The measurement device in six degree of freedom was utilized for revealing the effect of five types' lingual compornents of wrought wire Akers clasp system on the canine abutment movement, especially tipping movement. From this in vitro study the following conclusions could be drawn : 1) On comparing the tipping movement of each design with the design 1 as the control, no significant difference was found between any two designs regarding inclination of the abutment tooth. 2) The tipping direction of designs 2 and 4 with an ordinary lingual rest was mostly towards labial direction, but the inclination of designs 3 and 5 without an ordinary lingual rest, and design 1 considered as a specific type without an ordinary lingual rest and a reciprocal compornent such as a hook also was all towards lingual direction. 3) No significant difference was also recognized between the magnitude of inclination of the abutment tooth in crushing short type test food and that of the abutment tooth in crushing long type test food, although the latter inclination tended to be greater than the former one. 4) In comparing the magnitude of inclination of the working side abutment with that of the balancing side abutment tooth the former had a tendency to be greater excepting that of design 1, but there was no significant difference between the magnitude of inclination of either side. 5) Significant difference of ninety nine per cent confidence levels was recognized between tipping magnitude in unilateral loading and one in bilateral loading, and the latter was larger than the former. On the basis of the foregoing findings, the lingual compornent shapes of the wrought wire clasp systems has influence upon the canine abutment movement but the influence was found to be very small, especially on the magnitude of inclination. However, on tipping direction of the abutment tooth, the indicatioin was that it was influenced considerably in the same manner as that of cast Akers clasp systems.

The dynamic behaviour of a lower complete denture during unilateral loads: analysis using the finite element method

The purpose of this study was to analyse the correlation between the location and/or direction of unilateral load and the dynamic behaviour of a mandibular complete denture using the three‐dimensional finite element method (FEM). The FE model consisted of the body of mandible, alveolar mucosa, and a complete denture, and it could simulate the condition of contact between the surface of the mucosa and mucosal surface of a denture. Load vectors, which simulated premature contacts, were calculated on the supposition that a premature contact on an occlusal facet causes a vertical load on it. Load‐A, a load vertical to the anterior occlusal facet, caused the least displacement of the denture and less concentrated stress distribution. Load‐P, a load vertical to the posterior occlusal facet, was characterized by the stress distributed in the lingual area of the pre‐molar lesion on the contra‐lateral side of the load. Load‐B, a load vertical to the balancing occlusal facet, caused the largest displacement of the denture. The relationship between loads and stress distribution was agreed approximately with the observations previously reported, and lead to some suggestions about occlusion for complete dentures.

The dynamic behaviour of a lower complete denture during unilateral loads: analysis using the finite element method.

The purpose of this study was to analyse the correlation between the location and/or direction of unilateral load and the dynamic behaviour of a mandibular complete denture using the three-dimensional finite element method (FEM). The FE model consisted of the body of mandible, alveolar mucosa, and a complete denture, and it could simulate the condition of contact between the surface of the mucosa and mucosal surface of a denture. Load vectors, which simulated premature contacts, were calculated on the supposition that a premature contact on an occlusal facet causes a vertical load on it. Load-A, a load vertical to the anterior occlusal facet, caused the least displacement of the denture and less concentrated stress distribution. Load-P, a load vertical to the posterior occlusal facet, was characterized by the stress distributed in the lingual area of the pre-molar lesion on the contra-lateral side of the load. Load-B, a load vertical to the balancing occlusal facet, caused the largest displacement of the denture. The relationship between loads and stress distribution was agreed approximately with the observations previously reported, and lead to some suggestions about occlusion for complete dentures.

Effect of single-limb inertial loading on bilateral reaching: interlimb interactions.

This study employed the paradigm of asymmetric limb loading during bilateral arm reaching to examine the motor system's ability to independently organize the discrete movement of both upper limbs to equidistant targets when one of the limbs is loaded under specific timing constraints. The loading procedure involved attaching two different Velcro strapped weights to the right wrist, thus increasing the right arm's mass by 25% (1 kg) and 50% (2 kg). Movements were captured by a high-speed digital camera (240 Hz), while electromyographic (EMG) activity of selected elbow and shoulder muscles of both limbs was recorded (1,000 Hz) simultaneously. The results revealed that the mechanisms used by the system to compensate for unilateral limb loading were as follows: First, addition of an inertial load resulted in an increased movement time and concomitant decrease in peak velocity of both the upper arm and forearm of only the loaded limb and was scaled to the added weight. Second, for the EMG parameters, adjustments to the inertial load were primarily characterized by an increase in burst duration of all muscles, with load-specific changes in activity and onset time: the elbow antagonist (biceps) demonstrated a decrease in activity with the 50% load, and the elbow agonist (triceps) had an earlier onset with the 25% load. Concomitant adjustments on the unloaded limb consisted primarily of an increase in burst duration of the shoulder and elbow agonists (pectoralis and triceps), an earlier triceps onset solely with the 25% load, and a decrease in activity of the biceps solely with the 50% load. Third, with the exception of biceps activity, the amplitude of EMG activity was invariant across changes in load for both the loaded and unloaded limb. This lack of modulation in activity may have been related to the inability of performers to meet the time constraint of simultaneous bilateral limb arrival to the end targets. This inability can be the result of an active strategy selection process to safeguard the actions against interference or alternatively it could simply be a consequence of the biomechanical properties of the system in relation to task constraints. These issues are discussed in the light of the present findings and those of previous studies.

Three-dimensional finite element analysis of the facial skeleton on simulated occlusal loading.

Development of predictive models of occlusal loading of the facial skeleton will be of value for prosthetic design in oral rehabilitation. A 3-D finite element (FE) model of a human skull, based on CT scans, was constructed to analyse strain and stress distribution in the facial skeleton caused by simulated occlusal loading. Vertical loads were applied simulating loading of the full maxillary arch and unilateral single point occlusal loading of maxillary molar, pre-molar, canine and incisor sites. Strain and stress regimes from Von Mises (VM) failure criteria and extension and compression diagrams showed even distribution of strain following loading of the full maxillary arch throughout the facial elements. For individual points, the highest VM concentrations were consistently located on the facial aspect several mm above the loading site. Strain trajectories divided into a 'V-shaped' pattern, from the loading point into medial and lateral branches with higher VM values in the medial. As the same load was applied from the posterior to anterior region, VM values increased on all facial areas. Strain patterns were less symmetric and there was an increase in strain in the alveolar arch and around the rim of the nasal cavity. The overall picture of the facial skeleton is of a vertical plate enabling it to withstand occlusal stresses by in-plane loading and bending in its own plane. The most efficient distribution of load was on maxillary full arch loading with the most unfavourable strain concentrations occurring on loading in the anterior region.

Renal endothelin ET(A)/ET(B) receptor imbalance differentiates salt-sensitive from salt-resistant spontaneous hypertension.

It is unclear why a subgroup of patients with essential hypertension develop salt-sensitive hypertension with progression of target organ damage over time. We evaluated the role of the renal endothelin (ET) system in the stroke-prone spontaneously hypertensive rat (SHRSP) model of salt-sensitive spontaneous hypertension (SS-SH) compared with the spontaneously hypertensive rat (SHR) model of salt-resistant spontaneous hypertension (SR-SH). Both strains were studied after either sham-operation on a normal diet (Sham) or after unilateral nephrectomy and high NaCl loading (NX-NaCl) with 4% NaCl in diet for 6 weeks (n=10, respectively). Systolic blood pressure (SBP) increased only in SHRSP-NX-NaCl compared with SHRSP-Sham (250+/-6 versus 172+/-5 mm Hg, P:<0.0001). SBP remained unchanged in SHR-NX-NaCl compared with SHR-Sham. In SHRSP-NX-NaCl animals, urinary albumin and ET-1 excretion, renal ET-1 mRNA expression, glomerulosclerosis index, and tubulointerstitial damage index were elevated compared with SHRSP-Sham (P:<0.05, respectively), whereas no significant changes were found in SHR after NX-NaCl. Urinary sodium excretion (U(Na(+))) was significantly reduced by 38% in SHRSP-NX-NaCl compared with SHR-NX-NaCl (P:<0.005, respectively). SHR animals showed a similar increase in both renal ET(A) and ET(B) receptor densities after NX-NaCl (2.2-fold, P:<0.05). In contrast, SHRSP-NX-NaCl developed a significantly more pronounced increase in ET(A) compared with ET(B) binding (4.7-fold versus 2.4-fold, P:<0.05, compared with SHRSP-Sham, respectively), resulting in a significant 2.1-fold increase in ET(A)/ET(B) receptor ratio only in the SHRSP-NX-NaCl (P:<0.05). Thus, activation of the renal ET system together with an increased ET(A)/ET(B) receptor ratio may contribute to the development and progression of SS-SH.

Prevalence of pain related to schoolbag carriage in adolescents

Study design: A descriptive qualitative and quantitative cross sectional study design was chosen.Objective: To investigate the prevalence of lower back, neck, and shoulder pain in 13 to 15 year old scholars in Pretoria, South Africa, and how it related to methods of school bag carriage and perceived weight of school bags.Summary of background data: Unilateral loading has been linked to scoliotic type curves in the adolescent spine. More recent studies have also found that the weight of school bags may be related to the experience of pain, but very little research has been done on the prevalence of this pain.Methods and materials: A stratified random sample of nine schools was drawn from a total of 98 schools in the Pretoria District of the Gauteng Department of Education. The sample of 250 Grade 8 and 9 scholars was randomly selected. A questionnaire of open and closed ended questions was administered with five main sections, namely: demographics, method of carrying school bag, perceived school bag weight, areas of experienced pain, and awareness of adverse postural effects of carrying a school bag.Results: Thirty two percent of the sample reported pain either in the lower back, neck and/or shoulders. Principle Component Analysis and Chi-square tests showed no relationship between how the school bag was carried (over one/two shoulders; in one hand; swopping sides) and scholars’ reports of pain. A high level of significance (0.001 &lt;p&lt;0.042) was found when perceived bag weight was compared to the scholars’ reports of pain.Conclusion: Scholars in the Pretoria area present with a 32% prevalence of pain in the lower back, neck and/or shoulders. This is strongly correlated with the perceived weight of their school bags, regardless of how the school bag is carried.

Renal HETA/ETB Receptor Disbalance Characterizes Progression to Salt Sensitive Malignant Hypertension in Spontaneous Hypertension

P99 It is unclear why a subgroup of patients with essential hypertension develop salt sensitive hypertension with progression to malignant hypertension and renal failure. We evaluated the role of the renal endothelin (ET)-system in this setting by investigating two animal models with either salt-resistant or salt sensitive spontaneous hypertension. We studied salt resistant spontaneously hypertensive rats (SHR) and salt sensitive stroke-prone spontaneously hypertensive rats (SHRSP) after either sham operation on a normal diet (Sham) or after unilateral nephrectomy and high NaCl loading (NX-NaCl) with 4% NaCl in diet for 6 weeks (n=10, respectively). Systolic blood pressure (SBP) increased only in SHRSP-NX-NaCl compared to SHRSP-Sham (250±6 vs. 172±5 mmHg, p&lt;0.0001) while SBP remained unchanged in SHR-NX-NaCl compared to SHR-Sham. Albuminuria increased 210-fold in SHRSP-NX-NaCl compared to SHRSP-Sham (p&lt;0.0001), but no significant change was observed in SHR-NX-NaCl. In SHRSP-NX-NaCl glomerulosclerosis index, tubulointerstitial damage index, renal ET-1 mRNA expression, and urinary ET-1 excretion were significantly elevated compared to SHRSP (p&lt;0.05, respectively), but no significant changes of these parameters were found in SHR after NX-NaCl. Urinary sodium excretion (U Na ) increased in both SHR and SHRSP after NX-NaCl, but U Na was significantly reduced by 60% in SHRSP-NX-NaCl compared to SHR-NX-NaCl (p&lt;0.0001). After NX-NaCl renal ETA and ETB receptor densities, obtained by Scatchard analyses, were elevated in both SHR and SHRSP (ETA: 2.2- and 4.7-fold, ETB: 2.2- and 2.4-fold, p&lt;0.05 respectively). However, ETA increase was significantly more pronounced in SHRSP-NX-NaCl, thus resulting in an 2.1-fold increase of ETA/ETB receptor ratio in SHRSP-NX-NaCl. We conclude that activation of the renal ET system in conjunction with an increased ETA/ETB receptor ratio may contribute to decreased U Na and higher susceptibility for the development malignant hypertension and kidney damage in salt sensitive spontaneous hypertension.

Time structure of a goal-directed bimanual skill and its dependence on task constraints

The aim of the study was to elucidate the underlying principles of bimanual coordination and to establish quantitative coordination criteria. Healthy human subjects were instructed to open a loaded drawer with the left hand and to grasp, lift and reinsert with the right hand a small peg in the drawer recess. This bimanual goal-oriented task was executed promptly and consistently after a few trials. The temporal structure of the individual limb actions was assessed for computing interlimb synchronization and temporal correlation. In all subjects, both hands were well synchronized at the goal with high intermanual correlation in reaching the goal (event times of drawer opening and grasping the peg). This temporal goal-invariance was independent of movement speed and of the highly variable timing of the individual hands and persisted when subjects were blindfolded. Unilateral loading of the pulling hand and cutaneous anesthesia of the left index finger and thumb used for grasping the drawer handle significantly increased the pull-phase. This slowing of the left hand was matched by an adaptive delay of the right non-disturbed hand, thus preserving goal invariance. As a working hypothesis, we propose that multimodal sensory signals generated in the leading arm be transmitted centrally to re-parameterize the non-disturbed arm.

Measurement of submucosal forces transmitted to dental implants.

Early loading of dental implants after placement is believed to be a major cause for premature implant failure. If a transitional denture or partial denture is used during the healing period, occlusal forces may be transmitted to the submerged implant, leading to poorly differentiated growth of bone cells and/or potential inhibition of osseointegration at the bone-implant interface. The objective of this study was to develop an experimental model to measure the force transmission and to characterize the effect of selected loading conditions and relief methods on the forces transmitted to the implant. The loading conditions studied included unilateral and bilateral loading of the prosthesis. Forces were measured at two different relief conditions (relief with and without soft liner) and were compared against a control with no relief. The results show that fabrication of the prosthesis with a proper relief at the implant-denture junction can eliminate the submucosal force transmission to the implant on loading the denture both under unilateral and bilateral loading conditions. When a soft liner is used at the relief site, the transmitted force is small, but a finite value is reproducibly recorded. With no relief, the submucosal force transmission is high and may adversely affect the healing process or osseointegration. The experimental model is valuable in measuring and understanding the submucosal forces that are transmitted to the implant by loading the transitional prosthesis, and such measurement may assist in the proper design of the prosthesis for improved clinical durability and for other uses.

Deformation of a rectangular plate under impulsive loading

We report the results of the experimental investigation of the behavior of a rectangular plate in the processes of cutting by linear shaped charges according to the axisymmetric and asymmetric modes of unilateral loading and fracture caused by the explosion of a linear charge. It is shown that the transverse velocities and displacements of the same points of the plate subjected to unilateral explosive cutting by shaped charges are much higher (almost by an order of magnitude) than the corresponding parameters for the other modes of fracture. We also observed that the values of longitudinal mass velocities and displacements in the case of bilateral cutting by shaped charges are 1.5–7.0 times higher than the same parameters for unilateral cutting and explosive fracture without using shaped charges. It is also shown that the longitudinal accelerations attain their maximum values in the case where the shaped charge is placed at a focal distance from the plate.

On wave interaction and diffraction from the junction of two curved plates under unilateral fluid loading

A general solution is developed which describes the acoustic and dynamic structural response generated at the junction of two curved plates subject to unilateral fluid loading. The plates are modelled by two–dimensional thin–shell theory, and the solution is found by applying the Wiener–ndash;Hopf technique to the dual integral equations for the unknown pressure on the plates. A simple method is presented for evaluating the Wiener–ndash;Hopf split functions in semi–analytic form. The general solution is found by expressing the pressure transform in terms of a polynomial function whose coefficients are determined by the conditions at the joint. Here we consider welded and clamped junctions, either of which requires four unknown coefficients to be determined. Several limiting cases are examined including the practically important ones where either one or both plates are flat. Various diffraction coefficients associated with the fluid–ndash;structure interaction are studied and numerical predictions are presented for the magnitudes of the diffracted acoustic and structural waves. Energy partition among the various wave types is also investigated. It is found that even the small curvature effects considered here can lead to significant coupling between flexural and longitudinal structural waves.

Finite Element Analysis of the Lower Lumbar Neural Arch Under Facet Loading

To evaluate the mechanical effect of the direction of facet load on the isthmus stresses of the lower lumbar neural arch, stress analyses were performed by using three-dimensional finite element models of isolated L4 and L5 vertebrae with particular emphasis on accurate discretization of the posterior elements. The bilateral symmetric or unilateral facet loads, with a constant magnitude, were applied within the sagittal and transverse planes. The largest maximal principal stress in the neural arch (the largest sigma(max)) tended to be qualitatively similar in L4 and L5. At the physiologic range, the largest sigma(max), observed on the anterior surface of the isthmus, was relatively insensitive to the sagittal plane loadings but sensitive to the transverse plane loadings. The values of the largest sigma(max) of L4 and L5 were low at the more frontally directed facet load. The magnitude and direction of the largest sigma(max) depended upon the facet loadings mainly on the ipsilateral side and partly on the opposite side. The results suggest that the direction of facet load, which may be characterized by the facet orientation, can have mechanical effects on the occurrence and direction of isthmic crack.