Small Ligament Research Articles

Ultraviolet laser-induced fragmentation of hydrocarbon fuel droplets

The present study aims to understand droplet fragmentation due to instabilities from the radiative heating process. We focus on the plasma-induced breakup mechanism of iso-octane and n-hexane droplets from the nucleation of holes through sheets and instabilities. The plasma generation inside the droplets leads to an intense explosion followed by fragmentation of the droplets. A droplet is suspended in the air using an acoustic levitator and exposed to ultraviolet nanosecond laser pulses. The droplet sizes used are in the range of 0.5–2 mm in diameter, and laser energies are 10–20 mJ per pulse. Initially, plasma formation followed by shock wave emission is observed during the impact of the laser pulse. Afterward, the droplet opens at one side and is stretched vertically to form a liquid sheet. The hole formation and its rapid growth result in the breaking of the thin liquid sheet. Small droplets and ligaments emerge from the circular edge of the sheet, which follows the well-known ligament distribution. This study reveals the detailed analysis of expansion dynamics, evolution of single and multiple holes, and instabilities associated with the liquid sheet. The results observed are categorized into four different mechanisms: (1) plasma formation followed by shock wave propagation, (2) droplet deformation, (3) sheet breakup through nucleation of holes followed by rapid growth, and (4) complete atomization.

Development of a toughened and antibacterial Poly(lactide acid) (PLA) with preserved strength by elemental sulfur-based bio-renewable dynamically crosslinked elastomers

The toughening of PLA is usually realized by blending with elastomers or plasticizers, but often conflicted with lowered mechanical strength and complicated preparation steps. In the current study, inverse vulcanization was used to synthesize a series of dynamically cross-linked polysulfide (SOA) elastomers based on refining by-product elemental sulfur, soybean oil (SO) and allyl glyceryl ether (AGE), which provides dynamically reversible S-S bonds, flexible triglyceride segments and reactive epoxy functions.Melt blended with PLA, the SOAs exhibit great toughening effects and produce droplet-matrix typed blends with good interfacial compatibilization verified by rheology. SOA composition was decisive in dictating toughening efficiency. A high AGE content induces self-polymerization of epoxy groups, resulting in dominance of permanent crosslinking in SOA, giving rise to rigid SOA particles with bad processability and dispersity in PLA, hence poor toughener cavitations under external forces with unsatisfying toughening effect. A high sulfur and low AGE content results in dominance of dynamic crosslinking, providing soft SOA particles in favor of processing and dispersion in PLA matrix with small domains and thin ligament thickness, thus favoring internal cavitation of SOA particles to achieve good toughness. However, the presence of unreacted sulfur with a too high sulfur content can mitigate the toughening effect. In particular, a highly toughened blend with optimized SOA composition (PLA-S50O25A25) was obtained with excellent toughness (elongation at break 235.7% and tensile toughness 76.5 MJ/m3) balanced by only slightly impaired strength (tensile strength 50–60 MPa and modulus ∼ 900 Mpa). Moreover, the PLA-SOA exhibits excellent broad-spectrum anti-bacterial effects. This study reported the unprecedented use of fully sustainable dynamically-crosslinked elastomers as tougheners of PLA, paving new ways for PLA modification with balanced stiffness-toughness and antibacterial activity.

Anterior cruciate ligament reconstruction: current concepts and latest thinking

Never has there been such focus on just one small ribbon-like ligament in the human body: the anterior cruciate ligament (ACL) is the most highly studied and highly written about ligament in the knee, and yet still, there seem to be many ongoing unknowns. Despite this, there seem to be even more so-called experts than papers, all with their own firm and didactic opinions. This review article provides a contemporary opinion on the subject of ACL tears and ACL reconstruction, with a focus on the diagnosis of ACL tears and the decision-making process, with respect to conservative versus surgical management. The review also discusses the topics of tunnel placement, graft options, internal bracing, the anterolateral ligament and, importantly, outcomes. This paper highlights that there are a number of different approaches and options, and emphasizes the importance of discussing the pros and cons of these options with your patients, thoroughly, with shared decision-making leading to fully informed consent.

Experimental study of impinging jets of gelled and liquid fluids

This work presents an experimental study on spray formation by unlike impingement of gelled ethanol with liquid water and liquid ethanol, and a comparison with spray formation by like impingement of gelled ethanol. High-speed shadowgraphy was utilized to analyze collision sheets, instabilities, breakup lengths and particles of sprays formed by colliding jets with 0.80 mm diameter with equal momentum and different collision angles and flow conditions. For unlike jet impingement, the sheet evolution and disintegration showed a mixture of patterns found in Newtonian and non-Newtonian fluids, such as complex structures with rails, holes, fishbone, detaching beads and ligaments. Regime transition for unlike impingement configurations is faster than for like impingement, consequently the breakup lengths for unlike impingement were significantly shorter than for like impingement. In general, the breakup lengths decreased for larger We or larger jet momentum values and increased for lower impingement angles. Despite the improvement in the atomization caused by unlike configurations, small ligaments remained in all sprays formed by unlike jets. The particle sizes and geometries for the different configurations were evaluated and compared in terms of circularity, percent area and Feret diameter. No significant differences of the spray regions were observed between the two unlike impingement settings.

Shear mechanical responses and cracking evolution mechanisms of flawed sandstone containing two circular holes

Shear tests on rectangular plate sandstone containing two pre-existing holes were performed to analyze the shear mechanical responses and cracking evolution mechanisms. With generation of the penetrating fracture surfaces, both shear stress and normal displacement show a dramatic drop. Then, during the shear slipping process, the shear stress increases once again due to wear and shear off of the surface asperities, and three different variation trends of the normal deformation including shear dilation, fluctuation, and shear contraction are respectively identified. The role of ligament length and normal stress on several key indices such as peak shear stress, peak normal displacement and residual shear stress was investigated. Violent AE (acoustic emission) responses occur along with penetration of the fracture surfaces, and in the shear slipping process, AE events continue to occur due to wear of surface asperities, while the increase rate of accumulative AE events declines. Cracks coalesced at the rock bridge and running through the rock matrix form the main failure planes of the samples. From the PFC2D simulation results, the crack clusters first initiate from hole-walls and coalesce at the rock bridge for a small ligament length, while first produce the main failure planes at the right/left rock matrix for a large ligament length. The total number of micro cracks shows a “calm → rapid increase → decreasing growth amplitude” variation during shearing, and the induced cracks become more concentrated for a larger normal stress, implying a cumulative damage of the failure surfaces.

The Use of Various Measurement Methods for Estimating the Fracture Energy of PLA (Polylactic Acid).

The essential work of fracture (EWF) and Izod/Charpy impact tests have been used to investigate the fracture toughness in the plane stress of brittle polymers. In this paper, we had three goals: first, we aimed to employ how to estimate PLA toughness in different geometries; then, we proposed to compare Izod and Charpy Impact toughness in the same geometry; finally, we intended to determine the difference between EWF toughness and dynamic toughness. The results showed that the EWF method could be applied to evaluate PLA fracture behavior with small ligaments (2-4 mm), while the dynamic test could be employed with larger ligaments (5-7 mm). A comparison of the two impact test results obtained the following conclusions: Charpy impact toughness was higher than Izod impact toughness in the same geometry, and the impact toughness under a notch angle of 90° was larger than that of an angle of 45°. Both EWF and dynamic tests can be used to explore PLA toughness with small ligaments. The fracture energy decreases with ligament size in the EWF test, but it increases in the dynamic test.

CASE STUDY OF A PARAVAGINAL HAEMATOMA FOLLOWING VAGINAL DELIVERY

We present the case of a primigravida who had an induced delivery for mild IUGR at 38+6weeks. She had a normal vaginal delivery with right mediolateral episiotomy and minimal vaginal bleeding. She complained of increasing rectal pain in the postpartum period. Vaginal examination revealed a large left sided vaginal haematoma with intact episiotomy wound site.The haematoma was evacuated ,wound exploration done and sutured in layers. Vaginal packing was done. Postoperatively she again complained of rectal pain. Urgent CT scan conrmed nding of a large left pararrectal haematoma with possibility of small left broad ligament extension. She was managed conservatively with vaginal and rectal packing, analgesics,intravenous antibiotics and 3units of packed red cell transfusion. Follow up ultrasound showed reduction in the size of the haematoma and eventual resolution. This case supports the conservative management of even large paravaginal haematomas, when surgical evacuation is technically difcult as long as the patient is clinically stable.

Mechanical Evaluation of Knee Ligament Allografts for Thumb Metacarpophalangeal and Finger Proximal Interphalangeal Reconstruction

Purpose This study evaluated knee collateral ligaments for use as allografts in small joint reconstruction in the hand, specifically the thumb metacarpophalangeal (MCP) joint ulnar collateral ligament (UCL) and the index finger proximal interphalangeal (PIP) joint radial collateral ligament (RCL), and compared them to the current gold standard, tendon autograft. Methods Uniaxial tensile testing was performed on native thumb MCP UCLs and index finger PIP RCLs and 2.5-mm–diameter grafts prepared from hemi-flexor carpi radialis (hemi-FCR) tendons and knee medial collateral ligaments (MCLs) cadaveric allografts. In situ angular testing was performed in thumb MCP and index finger PIP joints. Each MCP/PIP joint was secured to a mechanical testing system and cyclically loaded. The UCL/RCL was resected and reconstructed with either an MCL or hemi-FCR. Cyclic loading was repeated, followed by angular load to failure. Results Uniaxial testing of MCL allografts demonstrated greater ultimate stress, ultimate load, and elastic modulus than hemi-FCR grafts and native UCLs/RCLs. The maximum angular deviation of the reconstructed MCP and PIP joints was not significantly different compared with the intact joint with either an MCL or hemi-FCR graft. In situ load to failure demonstrated no differences in failure torque or angular stiffness between MCPs reconstructed with a hemi-FCR and MCL allograft, whereas reconstructed PIP joints demonstrated improved angular stiffness with an MCL allograft compared with a hemi-FCR. Conclusions Medial collateral ligament allografts demonstrated improved mechanical properties compared with hemi-FCR tendon grafts during uniaxial testing, and grafts performed equivalently in in situ testing of reconstructed thumb/finger joints. Clinical relevance Prepared knee ligament allografts may provide a viable graft material for use in reconstruction of small hand ligaments. This new allograft material avoids the need to harvest a tendon autograft and has a biologic structure similar to native hand ligaments. This study evaluated knee collateral ligaments for use as allografts in small joint reconstruction in the hand, specifically the thumb metacarpophalangeal (MCP) joint ulnar collateral ligament (UCL) and the index finger proximal interphalangeal (PIP) joint radial collateral ligament (RCL), and compared them to the current gold standard, tendon autograft. Uniaxial tensile testing was performed on native thumb MCP UCLs and index finger PIP RCLs and 2.5-mm–diameter grafts prepared from hemi-flexor carpi radialis (hemi-FCR) tendons and knee medial collateral ligaments (MCLs) cadaveric allografts. In situ angular testing was performed in thumb MCP and index finger PIP joints. Each MCP/PIP joint was secured to a mechanical testing system and cyclically loaded. The UCL/RCL was resected and reconstructed with either an MCL or hemi-FCR. Cyclic loading was repeated, followed by angular load to failure. Uniaxial testing of MCL allografts demonstrated greater ultimate stress, ultimate load, and elastic modulus than hemi-FCR grafts and native UCLs/RCLs. The maximum angular deviation of the reconstructed MCP and PIP joints was not significantly different compared with the intact joint with either an MCL or hemi-FCR graft. In situ load to failure demonstrated no differences in failure torque or angular stiffness between MCPs reconstructed with a hemi-FCR and MCL allograft, whereas reconstructed PIP joints demonstrated improved angular stiffness with an MCL allograft compared with a hemi-FCR. Medial collateral ligament allografts demonstrated improved mechanical properties compared with hemi-FCR tendon grafts during uniaxial testing, and grafts performed equivalently in in situ testing of reconstructed thumb/finger joints.

Effects of specimen size and stress ratio on fatigue crack growth after a single tensile overload

This paper investigates the effect of specimen size, stress ratio, and loading pattern on fatigue crack growth for centrally cracked low carbon steel specimens. Elastic-plastic calculations were conducted under cyclic loading based on FEM using the domain integral method. The computed fatigue lives were firstly verified against the experimental tests taken from the literature. The numerical calculations showed that thickness has no significant effect on crack growth at a given stress ratio under the constant amplitude loading pattern. While the thinner specimens revealed longer fatigue lives compared to the thicker specimens at a certain stress ratio due to the application of a single tensile overload. A remarkable reduction in fatigue lives with a clear acceleration in crack growth rates was noticed for specimens with a small ligament length-to-specimen width ratio. The retardation response due to the application of a single tensile overload depended on a particular combination of specimen size and stress ratio. The variation in the crack driving force due to the change in thickness and ligament length was investigated. The relation between the crack driving force and the local stress state ahead of the crack tip was also discussed.

Elongation Patterns of the Superficial Medial Collateral Ligament and the Posterior Oblique Ligament: A 3-Dimensional, Weightbearing Computed Tomography Simulation.

Background:Although length change patterns of the medial knee structures have been reported, either the weightbearing state was not considered or quantitative radiographic landmarks that allow the identification of the insertion sites were not reported.Purpose:To (1) analyze the length changes of the superficial medial collateral ligament (sMCL) and posterior oblique ligament (POL) under weightbearing conditions and (2) to identify the femoral sMCL insertion site that demonstrates the smallest length changes during knee flexion and report quantitative radiographic landmarks.Study Design:Descriptive laboratory study.Methods:The authors performed a 3-dimensional (3D) analysis of 10 healthy knees from 0° to 120° of knee flexion using weightbearing computed tomography (CT) scans. Ligament length changes of the sMCL and POL during knee flexion were analyzed using an automatic string generation algorithm. The most isometric femoral insertion of the sMCL that demonstrated the smallest length changes throughout the full range of motion (ROM) was identified. Radiographic landmarks were reported on an isometric grid defined by a true lateral view of the 3D CT model and transferred to a digitally reconstructed radiograph.Results:The sMCL demonstrated small ligament length changes, and the POL demonstrated substantial shortening during knee flexion (P = .005). Shortening of the POL started from 30° of flexion. The most isometric femoral sMCL insertion was located 0.6 ± 1.7 mm posterior and 0.8 ± 1.2 mm inferior to the center of the sMCL insertion and prevented ligament length changes >5% during knee flexion in all participants. The insertion was located 47.8% ± 2.7% from the anterior femoral cortex and 46.3% ± 1.9% from the joint line on a true lateral 3D CT view.Conclusion:The POL demonstrated substantial shortening starting from 30° of knee flexion and requires tightening near full extension to avoid overconstraint. Femoral sMCL graft placement directly posteroinferior to the center of the anatomical insertion of the sMCL demonstrated the most isometric behavior during knee flexion.Clinical Relevance:The described elongation patterns of the sMCL and POL aid in guiding surgical medial knee reconstruction and preventing graft lengthening and overconstraint of the medial compartment. Repetitive graft lengthening is associated with graft failure, and overconstraint leads to increased compartment pressure, cartilage degeneration, and restricted ROM.

Comparative study between quadriceps tendon sling and semitendinosus graft for medial patellofemoral ligament reconstruction

Background Acute patellar dislocation is a common knee injury. The main injured structure is the medial patellofemoral ligament (MPFL). This ligament is the main static stabilizer against lateral patellar dislocation. Many surgical techniques have been described for the management of MPFL tear. The gold standard graft used for reconstruction is the hamstring. This study was done to compare the results of quadriceps tendon sling with semitendinosus graft for MPFL reconstruction (MPFLR). Patients and methods A prospective comparative study was held on 62 patients in El-Hadra University hospital between March 2018 and November 2019. Patients were divided into two groups. Group A had quadriceps graft and group B had semitendinosus graft for MPFLR. Patients were matched for age, sex, and body mass index. All cases were assessed clinically and functionally over 12 months of follow-up. Results There was no statistically significant difference between the 2 groups regarding Lysholm, Tegner, International Knee Documentation Committee, Visual Analog Scale, and Kujala scores. However, there was a statistically significant difference regarding the SCAR score. Conclusion Quadriceps tendon sling is a reliable alternative for MPFLR, especially in patients with small patellae or previous anterior cruciate ligament reconstruction.

The ACL can hypertrophy in response to mechanical loading: an MRI study in elite athletes (157)

The ACL can hypertrophy in response to mechanical loading: an MRI study in elite athletes (157)

Spatially-resolved characterization of oil-in-water emulsion sprays

When an oil-in-water emulsion is utilized for application in a flat-fan spray, micrometer-sized oil droplets are thought to facilitate hole formation on the spray lamella, leading to an earlier breakup of the spray sheet and an increase in resulting droplet sizes. However, prior work has largely focused on changes to the mean or median droplet size, and has not examined the influence of oil-in-water emulsions on the complete droplet size distribution, as well as other droplet properties such as droplet shape and droplet velocity distributions in flat fan sprays. This study concerns the effects of pressure, spatial location, and application of oil emulsions on the resulting droplet size, eccentricity, as well as velocity distributions, all of which are crucial information in determining the dispersion dynamics of the droplets during the spray applications. Experiments were conducted with a TP6515 nozzle, with the abovementioned droplets information measured using digital inline holography (DIH). Results show that the DIH-inferred volumetric droplet size distributions (VDSD) span widely from sub-100 μm to over 2 mm in size. The application of an oil-in-water emulsion results largely in suppression of smaller droplets, while the VDSD is relatively insensitive to increasing the oil volume fraction beyond a critical level. DIH results are consistent with the observation that smaller ligaments are observed only in the breakup regions for the single-phase water sprays, which break up more violently and earlier than larger ligaments. It is these smaller ligaments that are suppressed in the oil-in-water emulsion, which yield sub-millimeter droplets, some with sizes approaching sub-100 μm dimensions, corresponding to driftable sizes in agricultural settings. Interestingly, the application of oil-in-water emulsion generally decreases the eccentricity more significantly at the center than at the edge of the spray fan. We attribute this decrease to the increase in lamella sheet thickness and thus decrease in characteristic shrinkage rates, consistent with observations of high speed shadowgraphs. In all instances, oil-in-water emulsion droplets have higher velocities than equivalent sized water droplets. We attribute this to the earlier action of the spray breakup process in the oil-in-water emulsion, reduced surface energy generation during breakup (larger droplets), and reduced energy dissipation during breakup with oil-in-water emulsions, leading to increased translational energy after the breakup process. Therefore, it appears that oil-in-water emulsion application simultaneously suppresses small droplet formation and increases droplet velocity, and hence spray penetration in agricultural application.

Late Holocene Ameghinomya antiqua shells from the Beagle Channel: A multi-proxy approach to palaeoenvironmental and palaeoclimatic reconstruction

It is important to understand the historical precedents of current situations to be able to anticipate where the current global environmental and climatic change may lead. Geo-historical data provide information beyond the limitations of instrumental data. This study aims to reconstruct components of the palaeoclimatic and palaeoenvironmental history of the Beagle Channel (BC) during the Late Holocene by using Ameghinomya antiqua shells. We use fossil and modern shells in a comparative analysis through a multiproxy approach, i.e., shell morphometrics, shell growth, and stable oxygen isotope ratios. A holistic analysis of all the proxies indicates that higher productivity occurred around 3542 yr B.P. in the BC, evidenced by more significant growth, size, and longevity in fossil specimens. In addition, smaller ligaments, cardinal teeth, and the pallial sinus in fossil specimens indicate a low-energy environment typical of a marine archipelago. Lastly, palaeotemperatures are estimated to be warmer than today, although the intensity may be overestimated due to the freshwater inflow that would change the salinity of the BC waters. Further analysis in Late-Holocene shells is essential for a more detailed environmental reconstruction around the southern tip of South America.

Size-dependent radiation damage mechanisms in nanowires and nanoporous structures

Nanostructures with a high density of interfaces, such as in nanoporous materials and nanowires, resist radiation damage by promoting the annihilation and migration of defects. This study details the size effect and origins of the radiation damage mechanisms in nanowires and nanoporous structures in model face-centered (gold) and body-centered (niobium) cubic nanostructures using accelerated multi-cascade atomistic simulations and in-situ ion irradiation experiments. Our results reveal three different size-dependent mechanisms of damage accumulation in irradiated nanowires and nanoporous structures: sputtering for very small nanowires and ligaments, the formation and accumulation of point defects and dislocation loops in larger nanowires, and a face-centered-cubic to hexagonal-close-packed phase transformation for a narrow range of wire diameters in the case of gold nanowires. Smaller nanowires and ligaments have a net effect of lowering the radiation damage as compared to larger wires that can be traced back to the fact that smaller nanowires transition from a rapid accumulation of defects to a saturation and annihilation mechanism at a lower dose than larger nanowires. These irradiation damage mechanisms are accompanied with radiation-induced surface roughening resulting from defect-surface interactions. Comparisons between nanowires and nanoporous structures show that the various mechanisms seen in nanowires provide adequate bounds for the defect accumulation mechanisms in nanoporous structures with the difference attributed to the role of nodes connecting ligaments in nanoporous structures. Taken together, our results shed light on the compounded, size-dependent mechanisms leading to the radiation resistance of nanowires and nanoporous structures.

Sacrospinous Fixation in the Gynecology Department of Hôpital du Mali

Sacrospinous fixation (SSF) or Richter’s intervention (RI) aims to treat genital prolapse by securing the posterior vaginal wall to the small sacrospinous ligament. It is performed by low approach and includes a dissection of the pararectal space, visual exposure of the sacrospinous ligament and a needle with strait needle holder with nonabsorbable threads. It is often associated with a more complex corrective procedure, including cystocele cure, vaginal hysterectomy and posterior myorrhaphy. The objective of this study is to report the results of SSF in the gynecology department of Hopital du Mali. A descriptive study was conducted from September 2014 to September 2015 concerning 37 patients operated on for uterine prolapse (UP). All patients with grade III UP were included in our study in whom a unilateral hysterectomy (UH) and sacrospinous fixation (SSF) were performed. All the patients were scheduled. Preoperatively they had benefited from an assessment and a pre-anesthetic consultation. Hospitalization of at least 24 hours prior to the operation was required. Postoperative follow-up was two years with a physical examination at 3 months, 9 months and 15 months, and phone calls between physical consultations. During the study period, we performed 37 RIs. The mean age of the patients was 48 years with extremes of 41 to 73 years. The large multiparity was found out in 35 cases (94.59%), the pauciparous were two with 3 deliveries for each. Long labor of more than 18 hours was found out in 9 patients (24.32%) and home delivery in 13 cases (35.13%). The duration of the occurrence of prolapse was at least two years and 35 patients were going through menopause. The type of anesthesia used for the surgery was spinal anesthesia for all patients. The average duration of the operation was 90 minutes. Complications occurred in three patients or 8.10% of cases, two cases of acute urine retention and one case of hematoma of the para-rectal space. The medium time of hospital stay was 5 days. The anatomical result was satisfactory in all patients. However, two patients presented with grade II rectocele one year after the operation. Sacrospinous fixation is a technique suitable for our patients who present with genital prolapse with extreme laxity of the suspension ligaments. Well done, it brings anatomical satisfaction and its complications are rare and slight.

Fibromatosis of small intestinal ligament: a case report

We provide a unique case of report of fibromation of small intestinal ligament in a patient with sigmoid colon cancer. This is the first case that one patient suffered these two kinds of tumor, as far as we know, there is no such case before. Due to his medical history of malignant cancer, so the fibromation of small intestinal ligament was suspected to be a metastatic lesion when it was found by radiologists, so operation had been performed. Finally, it was confirmed by pathological result. After the operation and postoperative chemotherapy, the two masses were removed and the patient had no significant complications, during follow-up, the patient is gradually recovering. In general, the disease should be taking into consideration when patient suffered malignant cancer, although it is very rare. In addition, ultrasound guided biopsy is a feasible method to diagnose the disease.

Laryngeal and soft palate valving in the harbour seal (Phoca vitulina).

Effective 'valving' in the upper aerodigestive tract (UAT) is essential to temporarily separate the digestive and respiratory pathways. Marine mammals are largely dedicated to feeding underwater, and in many cases swallowing prey whole. In seals, little work has been done to explore the anatomy and function of the UAT in the context of valving mechanisms that function to separate food and air pathways. Here we use videofluoroscopy, gross dissection, histology and computed tomography (CT) renderings to explore the anatomy of the larynx and soft palate in the harbour seal (Phoca vitulina), and generate models for how valving mechanisms in the head and neck may function during breathing, phonating, diving and swallowing. Harbour seals have an elevated larynx and the epiglottis may rise above the level of the soft palate, particularly in pups when sucking. In addition, the corniculate and arytenoid cartilages with associated muscles form most of the lateral margins of the laryngeal inlet and vestibule, and move independently to facilitate airway closure. The corniculate cartilages flex over the laryngeal inlet beneath the epiglottis to completely close the laryngeal vestibule and inlet. The vocal folds are thick and muscular and the medial margin of the folds contains a small vocal ligament. The soft palate has well-defined levator veli palatini muscles that probably function to elevate the palate and close the pharyngeal isthmus during feeding. Our results support the conclusion that harbour seals have evolved UAT valving mechanisms as adaptations to a marine environment that are not seen in terrestrial carnivores.

Numerical investigation of fluid-driven crack propagation and coalescence in granite specimen with two pre-existing flaws

Natural oil-gas-bearing rock formation generally contains a large number of discontinuities, which have a large influence on the cracking process inside the rock under high water pressure condition. Hence, a good understanding of the propagation and coalescence of fluid-driven cracks is important to improve the oil and gas exploitation efficiency. This study numerically investigates the fluid-driven crack propagation process in rock specimen possessing two pre-existing flaws using a fluid coupled discrete element method. The micro-parameters are first calibrated against the mechanical properties of the Lac du Bonnet granite. The numerical specimen models are generated by installing two flaws with different ligament angles, ligament length, and flaw angles. The injection test with a constant rate is then conducted to study the propagation and coalescence patterns in these pre-cracked numerical models. The numerical results show that a relatively large ligament angle is better to accelerate the crack coalescence in the specimen with two paralleled flaws. Numerical model possessing two pre-existing flaws with a small ligament length is inclined to traverse the ligament area. Overall, the results in this study reveal that the pre-existing flaws inside the rock have a significant effect on the fluid-driven cracking process and much attention should be paid to the crack propagation behavior when many discontinuities are associated in the oil-gas-bearing rock formation.

Real-time experiment investigations on the coupled thermomechanical and cracking behaviors in granite containing three pre-existing fissures

This paper investigates the coupled thermomechanical (TM) behavior, in real time, of granite containing three pre-existing fissures under uniaxial compression. The ligament angle spans from 75° to 120° with an interval of 15°, and the testing temperature varies from 25 °C to 700 °C. The strength and deformation of the granite are first considered as functions of the temperature and the ligament angle. The elastic modulus of the granite greatly decreases at 400 °C, and uniaxial compression strength of the granite substantially decreases at 600 °C. The fracturing behavior of the granite specimens depends on not only the temperature but also the fissure array. For relatively small ligament angles, the crack coalescence pattern only depends on the ligament angle, while for relatively large ligament angles, the crack coalescence pattern depends on both the ligament angle and the temperature. The granite specimens mainly exhibit tensile failure modes at 25–300 °C, the brittle-ductile transition occurs at 300 °C, the granite specimens experience a mixed tensile-shear failure mode at 300–400 °C, and they experience a shear failure mode at T = 400–700 °C. Moreover, the thermal damage of the granite is analyzed by thin section observation and electron microscopy scanning (SEM). Thermally induced micro-cracks in the granite mainly include intercrystalline cracks and intracrystalline cracks, which occur dramatically at T = 400–700 °C. Electron probe micro analyzer (EPMA) experimental results show that the physical properties of the granite are considerably affected by temperature, while the chemical composition of the minerals remains unchanged at T = 25–700 °C. The damage to the microstructure of the granite at high temperatures is caused by physical changes rather than chemical changes.