Tunnel Distance Research Articles

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Objectives The purpose of the study was to evaluate long-term follow-ups of stabilized acromioclavicular joint (ACJ) dislocations using button dynamic system applied via arthroscopic technique or mini-open. Material and methods The review included follow-ups of 40 patients (39 males, 1 female) who underwent 40 ACJ stabilization procedures with Arthrex DogBone button between 2014 and 2017 using arthroscopy (n = 28) or mini-open technique (n = 12). The mean age of the patients was 34 years (range, 15 to 59 years). Patient reported outcomes were evaluated with UCLA shoulder rating scale, American Shoulder and Elbow Surgeons (ASES) shoulder score and the Constant Shoulder Score (CSS). Coraco-Clavicular Distance (ССD) was measured on preand postoperative anteroposterior views. Postoperative AP view was used to measure Clavicular Tunnel Distance (CTD). Arthroscopy patients had available preoperative radiographs (n = 21), postoperative radiographs (n = 26) and patient reported outcomes (n = 18). Mini open group had available preoperative radiographs (n = 2), postoperative radiographs (n=8) and patient reported outcomes (n = 8). Results One hundred percent of Arthroscopy/Mini open (26/26) cases were rated as excellent and good on UCLA shoulder rating scale at a long-term follow-up. One hundred percent of Arthroscopy patients (18/18) were rated as excellent and good; 75 % (6/8) of Mini-open cases evaluated as excellent and 25 % (2/8) as good on ASES shoulder score. Sixty seven percent of Arthroscopy (12/18) patients were rated as excellent and 33 % (6/18) as good; 62 % (5/8) of Mini open cases evaluated as excellent and 38 % (3/8) as good. Neither fair nor poor results were observed in both groups. No statistically significant differences were detected in median scores between Arthroscopy and Miniopen groups (p > 0.05). Preoperative radiographs showed Tossy grade IV dislocation (n = 3) and Tossy grade III (n = 20). Distal clavicle fracture was diagnosed in 2 cases. Median preoperative CCD radiologically measured 15.5 mm in both groups (n = 23). Median postoperative CCD and CTD radiologically measured 6.12 mm and 28.9 mm in both groups (n = 35), correspondingly. Decrease in postoperative CCD was significantly different (p = 0.0003). No statistically significant differences in postoperative CCD were detected between Arthroscopy and Miniopen groups (p > 0.05). Statistically significant differences in preoperative CCD were observed in both groups (n = 15) using weight-bearing/no weight-bearing AP views (P = 0.0009). Conclusion Stabilization of dislocated ACJ with dynamic systems is the method of choice providing excellent and good outcomes rated by UCLA rating scale, ASES shoulder score and CSS at long-term follow-up. One-stage surgical treatment is an advantage of dynamic systems with no need of construct removal. Standard and weighted stress radiographs of the involved side indicate to ACJ injury in comparison with contralateral side. Further research is needed for a longer term follow-up with the bone reduction maintained with dynamic system.

Elastic analytical solution of shallow tunnel owing to twin tunnelling based on a unified displacement function

• Unified displacement function of cross-section of each tunnel owing to twin tunnelling. • Complex variable method and Schwartz alternating method. • Elastic analytical solution for ground displacement of twin tunnels • The laws of ground displacement field for twin tunnels. A unified displacement function is used as the displacement boundary condition of the cross-section of each tunnel, which can be used to capture the asymmetrical deformation behaviors about the horizontal and vertical center line . Complex variable method is adopted to obtain the analytical solution of a single tunnel. Based on the Schwartz alternating method, the analytical solution of twin tunnels is obtained and the correctness of the analytical solution of twin tunnels is verified. A series of analyses are carried out to investigate the effects of the displacement boundary condition of the tunnel cross-section and the distance of twin tunnels on the ground surface settlement trough curve and the ground displacement field. Based on the proposed method, the parameters of displacement mode of the cross-section of twin tunnels are calibrated through field monitoring data of the Bangkok Subway Tunnel project, and the displacement field of the whole ground are analyzed. The proposed method can provides guidance in the conceptual stage of the design process of twin tunnels.

Implant preloading in extension reduces spring length change in dynamic intraligamentary stabilization: a biomechanical study on passive kinematics of the knee.

Dynamic intraligamentary stabilization (DIS) is a primary repair technique for acute anterior cruciate ligament (ACL) tears. For internal bracing of the sutured ACL, a metal spring with 8mm maximum length change is preloaded with 60-80N and fixed to a high-strength polyethylene braid. The bulky tibial hardware results in bone loss and may cause local discomfort with the necessity of hardware removal. The technique has been previously investigated biomechanically; however, the amount of spring shortening during movement of the knee joint is unknown. Spring shortening is a crucial measure, because it defines the necessary dimensions of the spring and, therefore, the overall size of the implant. Seven Thiel-fixated human cadaveric knee joints were subjected to passive range of motion (flexion/extension, internal/external rotation in 90° flexion, and varus/valgus stress in 0° and 20° flexion) and stability tests (Lachman/KT-1000 testing in 0°, 15°, 30°, 60°, and 90° flexion) in the ACL-intact, ACL-transected, and DIS-repaired state. Kinematic data of femur, tibia, and implant spring were recorded with an optical measurement system (Optotrak) and the positions of the bone tunnels were assessed by computed tomography. Length change of bone tunnel distance as a surrogate for spring shortening was then computed from kinematic data. Tunnel positioning in a circular zone with r = 5mm was simulated to account for surgical precision and its influence on length change was assessed. Over all range of motion and stability tests, spring shortening was highest (5.0 ± 0.2mm) during varus stress in 0° knee flexion. During flexion/extension, spring shortening was always highest in full extension (3.8 ± 0.3mm) for all specimens and all simulations of bone tunnels. Tunnel distance shortening was highest (0.15mm/°) for posterior femoral and posterior tibial tunnel positioning and lowest (0.03mm/°) for anterior femoral and anterior tibial tunnel positioning. During passive flexion/extension, the highest spring shortening was consistently measured in full extension with a continuous decrease towards flexion. If preloading of the spring is performed in extension, the spring can be downsized to incorporate a maximum length change of 5mm resulting in a smaller implant with less bone sacrifice and, therefore, improved conditions in case of revision surgery.

2D Tunnel Field Effect Transistors (FETs) with a Stable Charge‐Transfer‐Type p+‐WSe2 Source

Abstract2D materials are highly promising for tunnel field effect transistors (TFETs) with low subthreshold swing and high drive current because the shorter tunnel distance and strong gate controllability can be expected from the van der Waals gap distance and the atomically sharp heterointerface formed independently of lattice matching. However, the common problem for 2D–2D TFETs is the lack of highly doped 2D materials with the high process stability as the sources. In this study, it is found that p+‐WSe2 doped by charge transfer from a WOx surface oxide layer can be stabilized by transferring it onto an h‐BN substrate. Using this p+‐WSe2 as a source, all‐solid‐state 2D–2D heterostructure TFETs with an Al2O3 top gate insulator, i.e., type‐II p+‐WSe2/MoS2 and type‐III p+‐WSe2/WSe2 are fabricated. The band‐to‐band tunneling and negative differential resistance trends are clearly demonstrated at low temperatures. This work suggests that high doped 2D crystal of the charge transfer type is an excellent choice as sources for TFETs.

Micro-scale assessment of the postoperative effect of anterior cruciate ligament reconstruction preclinical study using a 7.1T micro-magnetic resonance imaging.

High-field micro-magnetic resonance imaging (MRI) scanning may provide additional information for quantitative analysis of graft bone healing processes, thus serving as a promising supplementary method in graft and bone healing evaluation following anterior cruciate ligament reconstruction (ACLR) surgery during preclinical studies. The present study included 12 New Zealand white rabbits that underwent ACLR with polyethylene terephthalate (PET) ligament. At 4, 8, and 16 weeks following surgery, 4 rabbits were euthanized and knee joint samples were harvested for a 7.1T micro-magnetic resonance imaging (MRI) scan. The graft bone tunnel diameter and signal noise ratio (SNR) at the region of interest (ROI) were measured. Hematoxylin-eosin staining was performed at each time point to verify the graft bone healing process in histology. The bone tunnel diameter at the graft tunnel interface decreased over time in both femoral and tibial parts. Notably, the tunnel size was smaller than the diameter of the drilling Kirschner wire that was used to observe the femoral part and proximal site of the tibial part at 16 weeks following surgery. SNR research demonstrated that both the femoral and tibial part PET ligaments selected in the ROI exhibited a marked increase in SNR from the initial 4-week results. The micro-MRI result was consistent with that of histological analysis. Micro-MRI scanning was applied in an animal model that underwent ACL reconstruction surgery with PET ligament, and it was determined that micro-MRI is promising in quantitatively observing graft bone healing processes directly with a focus on graft tunnel distances and SNRs.

Safe range analysis of clear distance of twin shallow tunnels based on limit analysis and reliability theory

A method of analyzing the stability of twin shallow tunnels was presented using both limit analysis with nonlinear failure criterion and reliability theory. In the condition of nonlinear failure criterion, the critical clear distances of twin shallow tunnels were obtained by analyzing the change of surrounding pressure. A reliability model was established based on limit state equation, and the failure probability was solved by virtue of Monte Carlo method. Safety factor and corresponding clear distance of different safety levels were obtained by introducing a target reliability index. The scope of clear distance for different safety levels is described, which can be used as a supplement and improvement to the design codes of tunnels.

How to Avoid Graft-Tunnel Length Mismatch in Modified Transtibial Technique for Anterior Cruciate Ligament Reconstruction Using Bone-Patellar Tendon-Bone Graft.

BackgroundWe conducted this study to determine the optimal length of patellar and tibial bone blocks for the modified transtibial (TT) technique in anterior cruciate ligament (ACL) reconstruction using the bone-patellar tendon-bone (BPTB) graft.MethodsThe current single-center, retrospective study was conducted in a total of 64 patients with an ACL tear who underwent surgery at our medical institution between March 2015 and February 2016. After harvesting the BPTB graft, we measured its length and that of the patellar tendon, patellar bone block, and tibial bone block using the arthroscopic ruler and double-checked measurements using a length gauge. Outcome measures included the length of tibial and femoral tunnels, inter-tunnel distance, length of the BPTB graft, patellar tendon, patellar bone block, and tibial bone block and graft-tunnel length mismatch. The total length of tunnels was defined as the sum of the length of the tibial tunnel, inter-tunnel distance and length of the femoral tunnel. Furthermore, the optimal length of the bone block was calculated as (the total length of tunnels − the length of the patellar tendon) / 2. We analyzed correlations of outcome measures with the height and body mass index of the patients.ResultsThere were 44 males (68.7%) and 20 females (31.3%) with a mean age of 31.8 years (range, 17 to 65 years). ACL reconstruction was performed on the left knee in 34 patients (53%) and on the right knee in 30 patients (47%). The optimal length of bone block was 21.7 mm (range, 19.5 to 23.5 mm). When the length of femoral tunnel was assumed as 25 mm and 30 mm, the optimal length of bone block was calculated as 19.6 mm (range, 17 to 21.5 mm) and 22.1 mm (range, 19.5 to 24 mm), respectively. On linear regression analysis, patients' height had a significant correlation with the length of tibial tunnel (p = 0.003), inter-tunnel distance (p = 0.014), and length of patellar tendon (p < 0.001).ConclusionsOur results indicate that it would be mandatory to determine the optimal length of tibial tunnel in the modified TT technique for ACL reconstruction using the BPTB graft. Further large-scale, multi-center studies are warranted to establish our results.

Risk of fracture of the acromion depends on size and orientation of acromial bone tunnels when performing acromioclavicular reconstruction

Current techniques for anatomic repair of the dislocated acromioclavicular (AC) joint aim on reconstruction of the AC ligaments and utilize tunnels drilled through the acromion . This improves the stability of the reconstruction but might also increase the risk of fractures at the acromion. The purpose of this study was to evaluate the fracture risk for the acromion after transacromial tunnel placement for anatomic AC joint stabilization procedure. It was hypothesized that the risk of fracture of the acromion is correlated to size and orientation of bone tunnels commonly used for anatomic AC joint reconstruction. A finite element analysis was used to simulate multiple bone tunnels and incoming force vectors (lateral vs. superior). Different tunnels were analysed, horizontal meaning an anterior-posterior orientation versus a vertical inferior-superior orientation through the acromion. Two tunnel diameters were simulated (2.4 vs. 4.5mm). Furthermore, the tunnel length and distance between tunnels were altered. Forty-five cadaveric specimens (median age: 64years, range 33-71years) were utilized for data acquisition. Out of these, 30 specimens were used to evaluate basic tunnel orientations and drill diameters using a MTS 858 servohydraulic test system. With regard to the tunnel orientation and drill hole size, the loads to failure were limited. The acromion is at higher fracture risk, with a superior to inferior directed incoming force. Position, size and direction of bone tunnels influenced the loads to failure. Horizontal tunnels with a higher diameter (4.5mm) had the most impact on load to failure reduction. A long horizontal tunnel with a diameter of 4.5mm reduced the load to failure with medial direction of force to 25% of the native acromion. The identical tunnel with a diameter of 2.4mm reduced the load to failure to 61%. Both 2.4-mm horizontal tunnels with a medium and short length did not reduce the load to failure. Tunnels placed at the acromion did not result in an increased risk of fracture. However, descriptive data showed a tendency for an increased fracture risk if tunnels are placed at the acromion, especially in horizontal direction with diameters of 4.5mm. In addition, the pattern of fracture was dependent on the orientation of the bone tunnels and the size. However, the results indicate a "safe zone" for the placement of bone tunnels within the anterior half of the acromion, which does not affect the loads to failure at the acromion. Therefore, current techniques for anatomic AC joint reconstruction which utilize fixation of grafts or sutures at the acromion are safe within current ranges of tunnel placement and sizes.

Sight distance and horizontal curve aspects in the design of road tunnels vs. highways: Part II (trucks)

The design of road tunnels is an essential component in highway geometric design. The study implements reasonable criteria for obtaining the sight distance and horizontal curve requirements of road tunnels vs. open roadways while considering a significant number of trucks in the traffic stream. This document continues a previous study assuming that the design vehicle is a passenger car. The engineering principles for considering trucks in the traffic stream are similar i.e. the use of perception-reaction time and longitudinal friction characteristics for obtaining the sight distance (and developing horizontal curve radii values for highway design) is applicable for trucks as well. However, truck performance characteristics affect the longitudinal friction parameters, side friction parameters, maximum superelevation, and the horizontal sightline offset (HSO) e.g. tunnel pavement status is irrelevant for deriving trucks' sight distance. It is concluded that the critical concept for safe horizontal curve radii in road tunnels (as in open roadways) is the stopping sight distance. The analysis has shown that the equilibrium requirement generated lower horizontal curve radii for the whole range of design speeds. The driver position (left hand or right hand curve) has a considerable impact on the design values of horizontal curve radii. The horizontal curve radii analyzed for trucks in road tunnels are considerably lower than the open roadways' radii for certain lower range of design speeds (50–80km/h). However, the reduction percentage from open roads can be considered less significant in the higher range of design speeds (90–120km/h). The results are useful to improve traffic safety if the design vehicle is a truck.

Stability Analysis During the Construction of Large Cross-section Tunnel Through Contact Belt

Instability of surrounding rock and supporting crack, large deformation phenomenon frequently happens in period of the construction process of large cross-section tunnel through contact belt. Taking Malin tunnel project of Lanhai expressway through unconformable contact belt as background, impact of tunnel span and vertical distance between tunnel and contact belt on tunnel stability was analyzed by numerical simulation method. The results indicates that tunnel plastic zone and that of contact belt are more prone to link together with larger tunnel span at certain distance of tunnel and supporting structure safety would suddenly reduce; The zone affected by contact belt is divided into secondary section and primary section according to variations of tunnel stability, and special research work on tunnel design and construction scheme should be carried out in primary section. The results could provide basis and reference for the similar engineering design and construction.

Location of the tibial tunnel aperture affects extrusion of the lateral meniscus following reconstruction of the anterior cruciate ligament.

The anterior root of the lateral meniscus provides functional stability to the meniscus. In this study, we evaluated the relationship between the position of the tibial tunnel and extrusion of the lateral meniscus after anterior cruciate ligament reconstruction, where extrusion provides a proxy measure of injury to the anterior root. The relationship between extrusion and tibial tunnel location was retrospectively evaluated from computed tomography and magnetic resonance images of 26 reconstructed knees, contributed by 25 patients aged 17-31 years. A measurement grid was used to localize the position of the tibial tunnel based on anatomical landmarks identified from the three-dimensional reconstruction of axial computed tomography images of the tibial plateaus. The reference point-to-tibial tunnel distance (mm) was defined as the distance from the midpoint of the lateral edge of the grid to the posterolateral aspect of the tunnel aperture. The optimal cutoff of this distance to minimize post-operative extrusion was identified using receiver operating curve analysis. Extrusion of the lateral meniscus was positively correlated to the reference point-to-tibial tunnel distance (r 2 = 0.64; p < 0.001), with a cutoff distance of 5 mm having a sensitivity to extrusion of 83% and specificity of 93%. The mean extrusion for a distance >5 mm was 0.40 ± 0.43 mm, compared to 1.40 ± 0.51 mm for a distance ≤5 mm (p < 0.001). Therefore, a posterolateral location of the tibial tunnel aperture within the footprint of the anterior cruciate ligament decreases the reference point-to-tibial tunnel distance and increases extrusion of the lateral meniscus post-reconstruction. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1625-1633, 2017.

Optimization of Anteromedial Portal Femoral Tunnel Drilling With Flexible and Straight Reamers in Anterior Cruciate Ligament Reconstruction: A Cadaveric 3-Dimensional Computed Tomography Analysis

To use 3-dimensional custom CAD technology to evaluate how knee flexion angle affects femoral tunnel length and distance to the posterior wall when using curved and straight guides for drilling through the anteromedial portal (AMP). Six cadaveric knees were placed in an external fixator at various degrees of flexion (90°, 110°, 125°, and maximum 135° to 140°). Computed tomography scans were obtained at all flexion points for 3-dimensional point-cloud models. Using custom CAD software, surgical guides through the AMP were replicated along with virtual tunnels at each flexion angle. Distance from the posterior cortex and tunnel dimensions were collected after 8-mm and 10-mm tunnel creation. At 90° of flexion, the average tunnel length down the posterior aspect of 8-mm tunnel was 25.0mm (95% confidence interval [CI] 16.2-33.8) and 12.0mm (95% CI 7.3-16.7) for curved and straight guides, respectively; 31.0mm (95% CI 26.8-35.2) and 28.6mm (95% CI 24.8-32.4) at 110°; 33.8mm (95% CI 30.1-37.5) and 31.1mm (95% CI 26.8-35.4) at 125°; and 35.0mm (95% CI 34.1-35.9) and 35.5mm (95% CI 34.2-36.8) with maximal flexion. Values between curved and straight guides are significantly different (P < .001), with straight guides breaching the posterior wall at 90° and 110° of flexion in some specimens. The average distance to the posterior wall cortex was 0.9mm (95% CI-1.5 to 3.3) and-0.6mm (95% CI-2.3 to 1.1) for curved and straight guides, respectively, at 90° of flexion (P= .014); 2.3mm (95% CI-0.2 to 4.8) and-0.1mm (95% CI-2.4 to 2.2) at 110° (P= .001); 4.4mm (95% CI 2.8-6.0) and 3.9mm (95% CI 1.9-5.9) at 125° (P= .299); and 6.7mm (95% CI 6.2-7.2) and 8.3mm (95% CI 6.1-10.5) at maximal flexion (P= .184). Posterior wall blowout was noted when using 10-mm straight guides at both 90° (2 specimens) and 110° (3 specimens). Using 10-mm curved guides posterior blowout was noted in 1 specimen at 90°. Maximum footprint coverage occurred at 110° for straight guides and 90° for curved guides. When using the AMP, flexible guides and reamers result in a greater distance of the tunnel to the femoral cortex while preserving adequate tunnel length at lower knee flexion angles. To create long femoral tunnels without breaching the posterior cortex, the knee should be flexed to at least 110° for curved reamers and 125° for straight. Femoral tunnel drilling through the AMP using curved and straight reamers requires different degrees of knee flexion to achieve optimal tunnel dimensions.

Functional and computed tomography correlation of femoral and tibial tunnels in single-bundle anterior cruciate ligament reconstruction: Use of accessory anteromedial portal.

Background:An accessory anteromedial portal (AAMP) has been shown to be effective in placing an anatomically ideal femoral tunnel. It is well known that this is due to the independent femoral drilling which is possible with the AAMP. However very little is known regarding the significance of this reconstruction technique in influencing the functional outcomes of anatomic anterior cruciate ligament reconstruction (ACLR). This study documents the influence of tibial and femoral tunnel positions on functional outcomes of anatomic ACLR using the AAMP.Materials and Methods:41 patients who underwent anatomic ACLR between 2011 and 2013 were included in this prospective cohort study. The primary outcome involved the documentation of femoral and tibial tunnel positions with volume rendering imaging using a three-dimensional computed tomography (3D-CT) done at the end of 1 year. The tunnel position evaluations from the CT images were performed by an independent observer specializing in radiodiagnosis. Functional outcome measures included preoperative and postoperative Lysholm and International Knee Documentation Committee (IKDC) scores (subjective) documented by an independent investigator who was not involved with the surgical procedure, at the end of 1 year.Results:The minimum followup was 1 year. All patients achieved good clinical and functional outcomes postoperatively with no reported complications. Tunnel position evaluations with 3D-CT revealed the average tibial tunnel distance to be 15.5 mm (standard deviation [SD] =2.52) from the anterior border of the tibial plateau and the average femoral tunnel distance to be 14.33 mm (SD = 2.6) from the inferior margin of the medial surface of lateral femoral condyle and 13.72 mm (SD = 2.8) from the posterior margin of the medial surface of lateral femoral condyle. The average tunnel diameters were found to be 7.9 mm (SD = 0.72) for the tibial tunnels and 8.6 mm (SD = 1.07) for the femoral tunnels. Statistically significant correlation between the tibial tunnel distance and the IKDC scores with anterior placement of tibial tunnel were found; however, no such statistical relationship were found between the femoral tunnel positions and the functional outcome measures.Conclusion:AAMP gives an ideal approach to drill the femoral tunnel independently. However, the influence of this tunnel placement on long term functional outcomes of ACLR needs to be assessed on larger cohort of patients.

P-Type Tunnel FETs With Triple Heterojunctions

A triple-heterojunction (3HJ) design is employed to improve p-type InAs/GaSb heterojunction (HJ) tunnel FETs. The added two HJs (AlInAsSb/InAs in the source and GaSb/AlSb in the channel) significantly shorten the tunnel distance and create two resonant states, greatly improving the ON state tunneling probability. Moreover, the source Fermi degeneracy is reduced by the increased source (AlInAsSb) density of states and the OFF state leakage is reduced by the heavier channel (AlSb) hole effective masses. Quantum ballistic transport simulations show, that with V_{DD} = 0.3V and I_{OFF} = 10^{-3}A/m, I_{ON} of 582A=m (488A=m) is obtained at 30nm (15nm) channel length, which is comparable to n-type 3HJ counterpart and significantly exceeding p-type silicon MOSFET. Simultaneously, the nonlinear turn on and delayed saturation in the output characteristics are also greatly improved.

An innovative ex-vivo porcine upper gastrointestinal model for submucosal tunnelling endoscopic resection (STER).

Background and study aims: Submucosal tunnelling endoscopic resection (STER) is a novel endoscopic technique to remove submucosal tumour (SMT). We propose a novel, low cost simulator for training of techniques for STER. Patients and methods: The model consisted of an ex-planted porcine oesophagus, stomach and duodenum with marbles embedded surgically in the submucosal plane. Two expert endoscopists with experience in submucosal tunnelling and 5 board-certified endoscopists with no experience in submucosal tunnelling were recruited. Participants were asked to perform a diagnostic endoscopy and 2 STER procedures, 1 in the oesophagus and 1 in the stomach. They also answered a structured questionnaire. Factors including operative time, mucosal and muscular injury rate, injection volume and accuracy of endoscopic closure were assessed. Results: The median time for localization of all SMTs was 40.1 seconds for experts and 38.5 seconds for novices (P = 1.000). For esophageal STER, the length of mucosal incisions and tunnelling distances were comparable between the 2 groups. The median volume injected by the novice group was significantly lower than the experts (15 mL vs 42.5 mL (P = 0.05). The median tunnelling time per length was 25.9 seconds/mm for the experts and 40.8 seconds/mm for the novice group (P = 0.38). There was a higher rate of mucosal injury and muscular perforation in the novice group (8 vs 0; P = 0.05). For gastric STER, the length of mucosal incisions and tunnel distances were comparable between the 2 groups. The median tunnelling time per length for the experts was 23.3 seconds/mm and 34.6 seconds/mm for the novice group (P = 0.38). One mucosal injury was incurred by a novice. The rate of dissection in the stomach and the oesophagus was not statistically different (P = 0.620). All participants voted that the model provides a realistic simulation and recommended it for training. Conclusions: STER is an advanced endoscopic technique where its indication is currently explored. Experienced and novice STER endoscopists have expressed the usefulness of this model as a training tool. This low-cost model can be used for future research in STER.

A charge inverter for III-nitride light-emitting diodes

In this work, we propose a charge inverter that substantially increases the hole injection efficiency for InGaN/GaN light-emitting diodes (LEDs). The charge inverter consists of a metal/electrode, an insulator, and a semiconductor, making an Electrode-Insulator-Semiconductor (EIS) structure, which is formed by depositing an extremely thin SiO2 insulator layer on the p+-GaN surface of a LED structure before growing the p-electrode. When the LED is forward-biased, a weak inversion layer can be obtained at the interface between the p+-GaN and SiO2 insulator. The weak inversion region can shorten the carrier tunnel distance. Meanwhile, the smaller dielectric constant of the thin SiO2 layer increases the local electric field within the tunnel region, and this is effective in promoting the hole transport from the p-electrode into the p+-GaN layer. Due to the improved hole injection, the external quantum efficiency is increased by 20% at 20 mA for the 350 × 350 μm2 LED chip. Thus, the proposed EIS holds great promise for high efficiency LEDs.

Effect of twin-parallel tunnels on seismic ground response due to vertically in-plane waves

In this paper, the effects of two long unsupported parallel tunnels on the seismic response of the ground surface are studied, using the boundary element method in the time-domain. The medium is assumed to have a linear elastic constitutive behavior subjected to vertically in-plane propagating incident SV and P waves. The ground surface amplification pattern above underground single and twin tunnels are examined based on the several effective parameters such as wavelength of the incident wave, buried depth, and spacing distance of the twin tunnels. It is evident that the seismic ground response above tunnels may be different from that of free-field motions during the seismic events. Moreover, the embedded depth and spacing distance of the twin tunnels have significant influences on the amplification patterns on the ground surface. Finally, some amplification coefficients are presented, which could be used while introducing simple preliminary ideas for modification of the standard design spectra in building codes.

Three-Dimensional Ground Settlement Induced by Metro Tunnel Excavation Considering the Influence of Group Piles

Considering the influence of group piles, a prediction model for three-dimensional ground surface settlement induced by circular metro tunnels excavation in incompressible rock masses is proposed based on the stochastic medium theory and the shear displacement method. The surface settlement caused by the metro tunnel opening is divided into two parts. One part is soil mass settlement caused by the metro tunnel opening and calculated by the stochastic medium theory. The other part is the settlement induced by the friction force between the group piles and the soil mass around the metro tunnel cross section and calculated by the shear displacement method. The three-dimensional prediction of the ground surface settlement is obtained by the linear superposition of the two parts. The validation of the proposed prediction approach is proved by comparing with the measured data and the numerical model of the double tunnels under thePuyuanoverpass where metro tunnels undercrossed group piles. The effects of buried depth, radial convergences, center distance of double tunnels, position and size of piles, and group piles are analyzed and discussed. The improved prediction approach can be applied to calculate the three-dimensional ground settlement, especially for the metro tunnels crossing through group piles.

Correlation of Mineralogical and Textural Characteristics with Engineering Properties of Granitic Rock from Hulu Langat, Selangor

In this study, the study area was at Hulu Langat in order to study the relationship between mineralogical characteristics and mechanical properties of rock. The type of rock found is granitic rocks. In order to study and determine the mineralogical characteristics of the rocks, thin section of rocks were prepared. Some minerals that abundance was observed in the rocks are quartz, feldspar, mica, clay-rich minerals and accessory minerals. The same rock samples that were collected from 10 tunnel distances then tested to determine point load strength index, uniaxial compressive strength and tensile strength. The relationships between these properties and mineralogical characteristics are described by simple regression analyses.

Designing TBMs for subsea tunnels

ABSTRACT: Recent years have shown great advances in the feasibility of long subsea tunnels. Projects such as the Channel Tunnel, the Stoerebelt Tunnel or the Bosporus Crossing have pushed the boundaries of TBM tunneling technology and fueled the work on feasibility studies for even more challenging projects such as crossing the Qiongzhou or Gibraltar Straits. There are numerous geotechnical challenges such as wide variations of ground conditions, high operation pressures or long tunnel distances and finally geological uncertainties which must be solved in order to attempt such projects. Several operational challenges such as large muck quantities interventions under difficult conditions and long transport distances also have to be tackled. TBM manufacturer and construction industry have developed a number of approaches to these challenges which point into the right technical direction and have been proven successfully in recent experiences. Their further development will allow attempting several megaprojects which are currently under discussion. Keywords: TBM, High pressures, Long distance, Subsea, Large diameter