End Of Duct Research Articles

Physical Insight of the Source Data of a Two-Port Acoustic Source Model

The physical insight of the source data of two-port acoustic source model for a duct is studied in theoretical, experimental and numerical aspects respectively. Under the ideal acoustic boundary condition of full absorption at the duct ends, the state equation of two-port acoustic source model is discussed, and the physical insight of the source data is obtained through theoretical derivation. The experimental model of two-port acoustic source is established, and the source data have been measured by the method “with an external source”. The physical meaning of source data has been demonstrated through the experimental method. The numerical simulating model for the experiment system is built, and the source data obtained numerically are compared with those measured experimentally for research. From the comparison, it is concluded that the source data of two-port acoustic source model are the traveling wave propagating outside along the duct under the acoustic boundary condition of full absorption at duct ends.

Clinical selection of surgical methods for pure stenosis at the end of common bile duct: a report of 43 cases

Objective To explore the clinical selection of surgical methods for pure stenosis at the end of the common bile duct.Methods The clinical data of 43 cases of pure stenosis at the end of the common bile duct treated in this hospital from October 2003 to June 2009 were retrospectively analyzed.Of the 43 cases, 12 underwent endoscopic sphincterotomy（EST）, 9 sphincteroplasty of Oddi, 5 pancreaticoduodenectomy,8 Roux-en-y choledochojejunostomy and 5 choledocoduodenostomy,4 underwent drainage of the T tube after exploration of the biliary passage.Results Among 37 patients did not undergo the radical pancreaticoduodenectomy,6 had space-occupying lesions 5-19 months postoperatively.Five of them received pancreaticoduodenectomy again.Conclusion Pure stenosis at the end of the common bile duct should be carefully managed. Key words: Common bile duct; Stenosis; Surgery

The Effect of Sampling Methods on the Apparent Constituents of Ink from the Squid Sepioteuthis australis

Results of experiments conducted on ink recovered from the squid Sepioteuthis australis indicate that there is no epinephrine or protein naturally present in the ink as it would be ejected in vivo. Protein content was effectively zero when ink was syringed from the duct end of the ink sac of freshly killed animals. By contrast, there were proteins in samples collected from dead specimens where ink was collected by a stripping method. From these samples, a single large molecular weight protein was identified as having tyrosinase activity. Digestion of syringed ink did not yield signs of melanin-bound proteins. Analysis of supernatants after centrifugation of squid ink consistently revealed the presence of DOPA, dopamine, and taurine, whereas epinephrine and nor-epinephrine were recorded from what was believed to be contaminated ink. Histological investigations of the ink sac revealed a compartmentalised glandular structure distal to the duct end. Closer observation of the glandular tissue showed that compartments increased in size as they matured and moved further into the lumen. It was concluded that the presence of epinephrine and tyrosinase (or a related protein) in the ink of S. australis could be attributed to rupturing of basal glandular compartments or contamination from other sources during the extraction process.

Differential Features of Pancreatobiliary- and Intestinal-type Ampullary Carcinomas at MR Imaging

To define the differential imaging features of pancreatobiliary- and intestinal-type ampullary carcinomas at magnetic resonance (MR) imaging and to correlate these features with pathologic findings. This retrospective study was approved by the institutional review board; informed consent was waived. Fifty patients with surgically confirmed ampullary carcinoma and preoperative MR results were included. Two radiologists, blinded to histologic type of cancer, evaluated imaging findings in consensus. Univariate and multiple logistic regression analysis were performed to define imaging findings that were useful for differentiation of the two types of carcinomas. On the basis of hematoxylin-eosin and immunohistochemical staining, 35 patients were classified as having pancreatobiliary type; and 15 patients, intestinal type. At MR, all of 15 intestinal carcinomas were nodular, whereas 16 (46%) of 35 pancreatobiliary carcinomas were infiltrative. Intestinal carcinomas were isointense (13 [87%] of 15) to hyperintense (two [13%] of 15), whereas 34% (12 of 35) of pancreatobiliary carcinomas manifested as hypointense compared with the duodenum on T2-weighted MR images (P = .034). Intestinal carcinoma commonly manifested with an oval filling defect at the distal end of the bile duct on MR cholangiopancreatographic (MRCP) images (11 [73%] of 15 vs four [11%] of 35 in pancreatobiliary type) (P < .001). At endoscopy, intestinal carcinoma manifested with an extramural protruding mass (n = 15, 100%) with a papillary surface (n = 11, 73%), whereas pancreatobiliary carcinoma manifested with intramural protruding (n = 5, 28%) or ulcerating (n = 1, 6%) gross morphologic features (P = .047) with a nonpapillary surface (n = 17, 94%) (P < .001). Multiple logistic regression analysis showed that an oval filling defect at the distal end of the bile duct was the only independent finding for differentiating intestinal from pancreatobiliary carcinoma (P = .027). An oval filling defect at the distal end of the bile duct on MRCP images and an extramural protruding appearance with a papillary surface at endoscopy are likely to suggest intestinal ampullary carcinoma.

Vortex cavitation and oscillation in a double-suction volute pump

In recent years, Computational Fluid Dynamics (CFD) codes have been utilized actively in the early part of the product development cycle. Numerical analysis models have also been developed rapidly and have added cavitation flow analysis functions peculiar to hydraulic machines, in which the flow analysis has been developed remarkably with high-precision and high-reliability. On the other hand, it is well known that three kinds of cavitation, such as vortex cavitation, reverse flow cavitation and cloud cavitation appear in a double-suction volute pump. We have much interest in a relationship among the cavitating flows, pump oscillation and noise. In this study, full 3D numerical simulations have been performed using a commercial code inside the pump from the inlet of suction duct to the outlet of delivery duct. The numerical model is based on a combination of multiphase flow equations with the truncated version of the Rayleigh-Plesset model predicting the complicated growth and collapse process of cavity bubbles. This study highlights especially the mechanism of vortex cavitation occurrence from the end of the suction duct in the pump and pump oscillation which causes cavitation noise from the pump. The experimental investigations have also been performed on the cavitating flow with flow visualization to evaluate the numerical results.

Is it necessary to accompany probing with endoscopy in cases of congenital nasolacrimal canal obstruction?

Objective To compare the results of probing with and without endoscopy in cases of congenital nasolacrimal duct obstruction who had previously not undergone probing. Methods Fifty-one children with congenital nasolacrimal duct obstruction who underwent surgical intervention between June 2007 and April 2009 in our hospital were included in the study. Patients who had had previous probings were excluded from the study. Conventional probing was performed in 37 eyes of 25 patients, and probing with intranasal endoscopic visualization in 36 eyes of 26 patients. Diagnosis was based on history of epiphora since birth or shortly after, and fluorescein dye disappearance test. Results Thirty-two of 37 eyes (86.48%) were cured by probing. Of the 5 cases with complaints, 1 had lacrimal sac fistula. Thirty-four of 36 eyes (94.44%) were cured by probing guided by endoscope observation. Thirty-two cases had stenosis at the lower end of the nasolacrimal duct which required probing. In two cases the probe passed submucosally to the floor of the nose. In two cases a false passage was made at the upper end of the inferior meatus. In these cases, the operation was continued by repeating the process until the distal end of the nasolacrimal canal was seen to have been passed. Conclusion Probing with endoscopy may be excessive in primary cases but in cases which have undergone unsuccessful probing, it is useful for visualization of anomalies in the lower nasolacrimal canal and to obtain the correct anatomic position for the probe.

Endoscopic ultrasound in biliary fasciolosis

A 16-year-old woman presented with recurrent episodes of severe upper abdominal pain and vomiting of 3 years duration. Multiple upper gastrointestinal scopies and ultrasonographies (USG) were normal. CT scan of abdomen had revealed mild intrahepatic biliary radical dilatation up to the lower end of common bile duct (CBD), but no stones or mass lesion. Her amylase and lipase levels during attacks of pain were normal. She was labeled as suffering from depression and was on antidepressants. Her liver function tests were normal except deranged alkaline phosphatase (178 IU/L). Clinical examination was unremarkable. Endoscopic ultrasound (EUS) revealed dilated CBD with a 3–4 cm floating and moving structure in the mid CBD coming down into the lower CBD with appearance like fluke (Fig. 1a). A biliary sphincterotomy was performed and a leaf like live worm was extracted with balloon catheter (Fig. 1b). Microbiological examination revealed diagnosis of Fasciola gigantica. She received a course of antihelminths and is asymptomatic on follow up of 9 months. Conventional USG in biliary fasciolosis usually reveals biliary dilatation, irregular thickened walls and worms are seen as vermiform structures without acoustic shadowing. USG is believed to be helpful in diagnosis of biliary fasciolosis, it may miss distal CBD lesions. EUS is an accurate investigation for imaging the lower biliary tree. Its role in the diagnosis of biliary fasciolosis has been documented earlier [1].

Diagnostic accuracy of multidetector‐row computed tomography for hilar cholangiocarcinoma

The aim of this study was to investigate the diagnostic reliability of multidetector-row computed tomography (MDCT) for the evaluation of tumor spread in hilar cholangiocarcinoma. Images obtained from a 16-detector row scanner of 22 patients were interpreted. The diagnostic accuracy of longitudinal ductal spread, vertical invasion (including hepatic parenchyma), and lymph node metastasis was assessed with reference to histopathological findings. The location of the tumor was correctly diagnosed in 95% of cases (21/22), but in five of these cases, the cut end of the intrahepatic bile duct was positive, resulting in 77% diagnostic accuracy for longitudinal spread. Among the patients with a negative bile duct surgical margin, there was a significant difference in the measurement of tumor spread between MDCT and microscopic investigation (P < 0.001). For vertical invasion, the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of MDCT were 69%, 100%, 100%, and 69% for the liver parenchyma, respectively. The sensitivity, specificity, PPV, and NPV of MDCT for lymph node metastasis were 50%, 75%, 43%, and 80%, respectively. The diagnostic accuracy of MDCT for tumor location and vertical invasion was satisfactory, but ductal spread was underestimated in comparison with microscopic measurements.

120 天井埋込型換気扇をモデルとする二自由度共鳴空洞の特性 : 空洞に内包した吸音材の効果(機械騒音の改善技術)

Some ceiling-mounted ventilators have the function of sound attenuation by a resonant effect in a chamber consisting of a rectangular outer cover and a cylindrical fan unit. The properties of the chamber have been studied using several simple models of the chamber by measurements and numerical calculations. The chamber consisting of two specific regions basically behaves as a Helmholtz resonator of two degrees of freedom. In this research, the second region of the chamber is filled with an absorbing material (a fibrous material). The effect of it on the sound attenuation properties of the chamber is studied experimentally using an axisymmetric chamber located at the end of a hemi-infinite duct. The frequency response of the chamber changes from that of two degrees of freedom to that of single degree of freedom as the density of material increases. While the sound attenuation level falls around the resonant frequencies, it rises in the intermediate frequency range. The properties are also examined by numerical calculations using a FEM software that gives reasonable results to describe the measured results. In the present model, the flow resistivity of the material is the decisive valuable among the several valuables defining a porous material. As the effect of the absorbing material, the resonant character diminishes in the sound field of the chamber.

A newly discovered sperm transport system in the female of Lygaeidae bugs

In the female reproductive system of the relatively large hemipteran, the western conifer seed bug Leptoglossus occidentalis (Heidemann), a cuticle-lined tube extends medially along the surface of the vagina from the proximal end of the spermathecal complex anteriorly to the base of the common oviduct. This medial tube houses the proximal end of the spermathecal duct, thereby enabling the transport of material from the spermatheca at the distal end of the spermathecal complex, past the vagina (or bursa copulatrix) and directly to the common oviduct. The proximal portion of the spermathecal complex also contains an insemination duct that is separate from the spermathecal duct. The insemination duct allows the male intromittent organ to extend from the vagina to the spermatheca without navigating through the spermathecal duct. The reproductive systems of two previously studied Hemiptera, the milkweed bug Oncopeltus fasciatus (Dallas) and the box elder bug Leptocoris trivittatus (Say), possess a similar cuticle-lined medial tube housing the spermathecal duct. This new information provides a clearer understanding of sperm transport in the female reproductive system of Lygaeidae bugs, and helps to clarify the path of the male organ during copulation, as well as the movement of sperm during egg laying.

Acoustic mode radiation from the termination of a truncated nonlinear internal gravity wave duct in a shallow ocean area

Horizontal ducting of sound between short-wavelength nonlinear internal gravity waves in coastal environments has been reported in many theoretical and experimental studies. Important consequences arising at the open end of an internal wave duct (the termination) are examined in this paper with three-dimensional normal mode theory and parabolic approximation modeling. For an acoustic source located in such a duct and sufficiently far from the termination, some of the propagating sound may exit the duct by penetrating the waves at high grazing angles, but a fair amount of the sound energy is still trapped in the duct and propagates toward the termination. Analysis here shows that the across-duct sound energy distribution at the termination is unique for each acoustic vertical mode, and as a result the sound radiating from the termination of the duct forms horizontal beams that are different for each mode. In addition to narrowband analysis, a broadband simulation is made for water depths of order 80 m and propagation distances of 24 km. Situations occur with one or more modes absent in the radiated field and with mode multipath in the impulse response. These are both consistent with field observations.

Ultrasonic scalpel for sealing of the thoracic duct: evaluation of effectiveness in an animal model

To verify the usefulness of an ultrasonic scalpel for the sealing of lymphatic ducts, a Harmonic Ace scalpel (Ethicon Endo-Surgery, Inc, Cincinnati, OH) was tested, using the thoracic ducts in pigs. Indocyanine green was injected into the abdominal lymphatic ducts in two pigs, and the stained thoracic ducts were identified. The thoracic ducts were then divided and sealed into seven sections with a Harmonic Ace scalpel, used at a power setting of level 3. The cut ends of the thoracic ducts were evaluated macroscopically, histologically, and by measuring bursting pressure. The whole length of thoracic duct of each pig was clearly imaged by pigment. Each stump divided by the ultrasonic scalpel was completely sealed, and there was no pigment leakage from the cut end macroscopically. Histologic examination revealed that the cut end was sealed by homogenous degenerative coagulation. Bursting pressures could be determined at three cut ends of thoracic ducts and were 195 mmHg, 188 mmHg, and 203 mmHg, respectively. The thoracic ducts were reliably divided and sealed by an ultrasonic scalpel in pigs. This device is expected to be a useful tool for the surgical treatment of chylothorax.

Sound reflection at the open end of axisymmetric ducts issuing a subsonic mean flow: A numerical study

This paper investigates the reflection of sound waves as they propagate toward the open end of ducts issuing a cold subsonic mean flow in a stagnant fluid. The investigations are conducted by using a relatively new one-step numerical technique known as the lattice Boltzmann method. The results obtained in terms of end correction, l, and magnitude of the pressure reflection coefficient, | R | , for an unflanged pipe model are in very good agreement with theoretical predictions and experimental data for the range of Mach numbers M ≤ 0.15 and Helmholtz numbers ka ≤ 1.5 . Simulations carried out for a similar pipe terminated by circular horns of different curvature radii show that | R | is independent of the horn geometry for Strouhal numbers Sr 0 < 4 , Sr 0 = ka / M . For situations in which M > 0 , the amplification of the reflection coefficient magnitude, that is | R | > 1 , is normally ∼ 20 percent higher than that observed for an unflanged pipe issuing an equal Mach number flow. Furthermore, the amplification maxima is found to occur always at Sr 0 = π / 2 , regardless of whether the pipe is unflanged or terminated by different circular horns. Conversely, the results for the end correction are strongly dependent on the horn curvature. For the low Strouhal number limit, the dimensionless end correction measured at the junction between the horn and the pipe with radius a becomes l / a = 0.31 for a horn whose curvature radius is 2 a , and l / a = 0.62 for a horn with curvature radius equal to 4 a .

Pancreatic Stent Placement is Associated with Resolution of Refractory Grade C Pancreatic Fistula after Left-Sided Pancreatectomy

Pancreatic fistula have been a source of significant morbidity and mortality after left-sided pancreatectomy. The majority of fistulas are classified as Grade A and resolve quickly with no intervention. Grade C pancreatic fistulas, which require percutaneous or operative drainage, are less common and may be associated with morbidity and mortality. We used postoperative endoscopic pancreatic stent placement as an adjunctive strategy in the management of refractory Grade C pancreatic fistulas. Patients undergoing endoscopic pancreatic stent placement for persistent, refractory peripancreatic fluid collections/pancreatic fistula after left-sided pancreatectomy were identified. Eight patients underwent endoscopic pancreatic stent placement for refractory Grade C pancreatic fistulas. Six patients had percutaneous catheter placement; two patients had transgastric drainage. Endoscopic retrograde cholangiopancreatography (ERCP) showed extravasation of contrast from the distal end of the pancreatic duct in seven patients. Pancreatic stents were placed in all patients at a median time of 48 days postoperation and left for a median of 47 days. Before stent removal, ERCP demonstrated pancreatic fistula closure. Median time to complete resolution of the fistula was 41 days after stent placement. Endoscopic pancreatic stents were associated with resolution of Grade C fistulas. After distal pancreatectomy, pancreatic stent placement should be considered in the postoperative period for refractory pancreatic fistulas.

Pancreato‐enteric anastomosis: The duct evagination technique

Pancreatic anastomotic failure remains the most frequent and potentially life-threatening complication following Pancreatoduodenectomy. Numerous modifications in the technique of the pancreatoenteric anastomosis have been reported. We suggest a simple modification which involves "evaginating" the cut end of the pancreatic duct. This technique helps avoid a compromise of the pancreatic ductal patency, and by achieving a wide pancreatic ductal opening can facilitate a safer pancreato-enteric anastomosis. In addition, by possibly decreasing the likelihood of post-operative pancreatic ductal stenosis, it has the potential to reduce post-Pancreatoduodenectomy pancreatic exocrine insufficiency. The modification acts as an adjunct to an already established technique yielding good results.

Characteristics of Bile Duct Carcinoma with Superficial Extension in the Epithelium

Longitudinal tumor extension from the main tumor involves intramural or superficial spread along the bile duct, which influences surgical curability. Identifying the range of superficial extension is difficult by preoperative imaging. To clarify specific characteristics of bile duct carcinoma (BDC) with superficial extension of epithelium in the bile duct, we examined clinicopathologic features and patient outcomes in BDC patients with or without superficial extension who underwent surgical resection. Between 1994 and 2008, we retrospectively examined clinicopathologic findings and outcomes for 42 BDC patients who underwent surgical resection and divided them into two groups: (1) superficial extension (SE) group (n = 10); and (2) non-SE group (n = 32). In terms of macroscopic growth of the main tumor, the papillary type was more common in the SE group than in the non-SE group, whereas the nodular type was dominant in the non-SE group. The prevalence of cancer-positive findings at the cut end of the bile duct was higher in the SE group. Portal vein invasion was not observed in the SE group, and the prevalence of regional lymph node metastasis was significantly greater in the non-SE group than in the SE group. No patients died of cancer in the SE group, who tended to show better survival than the non-SE group. The present results suggest that a good prognosis may be achieved in BDC patients with SE when complete resection is accomplished.

Clinical and prognostic analysis of malignancies with multi-tumor factors in pancreas and periampullary region

Objective To investigate the biological features and treatment of malignancies with multi-tumor factors in the pancreas and periampullary region. Methods A retrospective clinical analy-sis was conducted on 18 cases of the malignancies admitted to our hospital during 2005.1-2007.5. The clinical features, imaging findings, therapeutic and pathological data were analyzed. Meanwhile, the prognosis of this kind of malignancies was compared with that of adenoductal cancer undergoing radical pancreateetomy and that of periampullary carcinoma receiving palliative operation. Results The ma-lignancies were found in 11 men and 7 women with a mean age of 62.4±11.7 years. Tumors were lo-cated in the pancreas,the lower end of common bile duct and the ampullary part of duodenum in 14 ca-ses, ampullary duodenum and common bile duct in 1, pancreas and gallbladder in 1, pancreas and common bile duct in 1 and papillary duodenum and beginning of duodenum in 1. Fifteen of them re-ceived pancreaticoduodeneetomy (PD), 2 resection of distal pancreas plus splenectomy and the others total pancreatectomy. Ten patients died of tumor recurrence or liver metastasis several months after operation. For the 8 patients who survived, the longest survival time was 18 months. The median sur-vival time for those patients was only 13.2 months, which was significantly shorter than 27 months for the adenoductal cancer receiving PD and 20.9 months for the periampullary carcinoma undergoing pal-liative therapy. Conclusion The malignancies with multi-tumor factors in the pancreas and periampul-lary region are located mainly in the head of pancreas and the lower part of common bile duet, among which combination of IPMC or adenoductal carcinoma with other rare types of malignancies were the most common histotypes. The prognosis of this kind of carcinoma is poor and needs further research. Key words: Pancreatic neoplasms; Multi-tumor factors

Balloon Catheter Dilation for Complex Congenital Nasolacrimal Duct Obstruction in Older Children

To evaluate the effectiveness of lacrimal balloon catheter dilation in the treatment of complex congenital nasolacrimal duct obstruction in older children. In a retrospective study, the case records of 65 eyes of 59 children 2 to 6 years (mean: 37 months) who underwent probing for congenital nasolacrimal duct obstruction were evaluated. Complex obstruction was noted in 21 (32.3%) of the 65 children older than 2 years who underwent probing. Secondary balloon dacryoplasty was performed in 8 (38.09%) of these 21 lacrimal systems. Patient age ranged from 3 to 6 years (mean: 47 months). Balloon catheter dilation was performed according to a standard protocol. Clinical patency of the nasolacrimal system was the main outcome measure and was defined as complete resolution of signs and symptoms (crusting, discharge, and watering) on follow-up. The procedures were performed under general anesthesia. All dilations were performed by the same lacrimal surgeon. Secondary balloon dacryoplasty was successful in seven of the eight lacrimal systems (87.5%). Complex obstruction at the distal end of the nasolacrimal duct was noted in all children. All children were older than 3 years (mean: 37 months), and all underwent secondary procedures because previous probing was unsuccessful. Balloon catheter dilation is an effective procedure for complex nasolacrimal duct obstruction in older children. It can be an alternative to silicone intubation and dacryocystorhinostomy in children after unsuccessful probing.

An equivalent-source model for simulating noise generation in turbofan engines

Nowadays, computational aeroacoustics (CAA) is used for simulating wave propagation in ducted turbofans, especially as computational fluid dynamics (CFD) is increasingly employed to model the identified noise sources. An efficient way to match the CFD and CAA domains is to make some assumptions on flow and duct geometry, so that disturbance fields can be expanded over incoming/outgoing acoustic modes. Based on this approach, this paper presents an original matching model in which the outgoing modes are generated by means of equivalent monopole distributions defined as source terms in the equations governing the acoustic propagation, instead of a conventional inflow boundary condition (BC). Advantages and limits of the method are discussed. The process to get back to the sources and its numerical implementing are described. Although initially focused on tones, an extension of the method to broadband noise generation is tackled too. The method then is validated on a simplified turbofan exhaust configuration. Numerical solutions obtained by implementing the source terms in a high-order time-domain Euler code are compared to analytical solutions, either in a uniform or in a radially shear mean flow (provided by RANS). The parallel shear flow solution is obtained by solving the Pridmore–Brown equation. The ability to accurately simulate the standing waves due to acoustic reflections at duct ends is also assessed by comparing the numerical solutions computed using both source-based and BC-based options in the Euler solver.

Closure of the Cystic Duct by Ultrasonic Energy

Ultrasonic activated devices are currently used both for sealing of blood vessels and dissection of parenchymal organs. Recently, ultrasonic energy has been used to seal the cystic duct during successful clip-less cholecystectomy, but no study examined the mechanisms of tissue welding by ultrasonic energy or the biomechanical properties of the seal. This was the aim of our investigations. Eight patients (7 women and 1 man, mean age 42+/-7 y) subjected to laparoscopic cholecystectomy had a cystic duct sealed and sectioned by Ultracision; after removal of the specimens, the distal end was processed for scanning electron microscopy and transmission electron microscopy, whereas the proximal end to the gallbladder was used for determination of the bursting pressure. The bursting pressure of the cystic duct sealed by ultrasonic energy was 168+/-47 mm Hg, well above the maximal pressure of the common bile duct. At scanning electron microscopy, the end of the cystic duct was closed by an amorphous, bundled, dense substance. The section proximal to the end showed destruction of the epithelial layer with dense amorphous bridges connecting the opposite sites of the wall. When the lumen was observed, it was filled with bile microaggregates. At transmission electron microscopy, 2 different findings were evident: (1) coagulative necrosis in the sectioned area and (2) a combination of coagulative necrosis and collagen denaturation in the more distal sections. The connective tissue was characterized by attenuation of collagen birefringence and swelling of fibers and bundles due to shrinkage of collagen. Ultrasonic energy can be applied to suitable tissues to obtain sealing of the walls with good biomechanical effects.