AlGaN nano-shell structure on a GaN nanorod formed with the pulsed MOCVD growth.

An AlGaN/GaN multi-shell structure on a GaN nanorod (NR) is formed by using the self-catalytic pulsed growth process of metalorganic chemical vapor deposition with Ga and Al/N supplies in the first and second half-cycles, respectively. With Al supply, a thin AlGaN layer is precipitated near the end of a growth cycle to form the AlGaN/GaN structure. Because of the lower chemical potential for GaN nucleation, when compared with AlN, a GaN layer is first deposited in a growth cycle. AlGaN is not precipitated until the AlN nucleation probability becomes higher when the catalytic Ga droplet is almost exhausted. Because the Al adatoms on the NR sidewalls hinder the upward migration of Ga adatoms for contributing to the Ga droplet at the NR top, the size of the Ga droplet decreases along growth cycle leading to the decrease of GaN layer thickness at the top until a steady state is reached. In this process, the slant facet of an NR changes from the (1-102)-plane into (1-101)-plane. To interpret the observed growth behaviors, formulations are derived for theoretically modeling the AlN nucleation probability, NR height increment in each growth cycle, and the time of exhausting the Ga droplet in a cycle.

Effects of Surface Plasmon Coupling on the Color Conversion of an InGaN/GaN Quantum-Well Structure into Colloidal Quantum Dots Inserted into a Nearby Porous Structure.

To further enhance the color conversion from a quantum-well (QW) structure into a color-converting colloidal quantum dot (QD) through Förster resonance energy transfer (FRET), we designed and implemented a device structure with QDs inserted into a GaN nano-porous structure near the QWs to gain the advantageous nanoscale-cavity effect. Additionally, surface Ag nanoparticles were deposited for inducing surface plasmon (SP) coupling with the QW structure. Based on the measurements of time-resolved and continuous-wave photoluminescence spectroscopies, the FRET efficiency from QW into QD is enhanced through the SP coupling. In particular, performance in the polarization perpendicular to the essentially extended direction of the fabricated pores in the nano-porous structure is more strongly enhanced when compared with the other linear polarization. A numerical simulation study was undertaken, and showed consistent results with the experimental observations.

Behaviors of AlGaN Strain Relaxation on a GaN Porous Structure Studied with d-Spacing Crystal Lattice Analysis.

The high porosity of a GaN porous structure (PS) makes it mechanically semi-flexible and can shield against the stress from the thick growth template on an overgrown layer to control the lattice structure or composition within the overgrown layer. To understand this stress shield effect, we investigated the lattice constant variations among different growth layers in various samples of overgrown Al0.3Ga0.7N on GaN templates under different strain-relaxation conditions based on d-spacing crystal lattice analysis. The fabrication of a strain-damping PS in a GaN template shields against the stress from the thick GaN template on the GaN interlayer, which lies between the PS and the overgrown AlGaN layer, such that the stress counteraction of the AlGaN layer against the GaN interlayer can reduce the tensile strain in AlGaN and increase its critical thickness. If the GaN interlayer is thin, such that a strong AlGaN counteraction occurs, the increased critical thickness can become larger than the overgrown AlGaN thickness. In this situation, crack-free, thick AlGaN overgrowth is feasible.

Effects of overgrown p-layer on the emission characteristics of the InGaN/GaN quantum wells in a high-indium light-emitting diode.

The counteraction between the increased carrier localization effect due to the change of composition nanostructure in the quantum wells (QWs), which is caused by the thermal annealing process, and the enhanced quantum-confined Stark effect in the QWs due to the increased piezoelectric field, which is caused by the increased p-type layer thickness, when the p-type layer is grown at a high temperature on the InGaN/GaN QWs of a high-indium light-emitting diode (LED) is demonstrated. Temperature- and excitation power-dependent photoluminescence (PL) measurements are performed on three groups of sample, including 1) the samples with both effects of thermal annealing and increased p-type thickness, 2) those only with the similar thermal annealing process, and 3) those with increased overgrowth thickness and minimized thermal annealing effect. From the comparisons of emission wavelength, internal quantum efficiency (IQE), spectral shift with increasing PL excitation level, and calibrated activation energy of carrier localization between various samples in the three groups, one can clearly see the individual effects of thermal annealing and increased p-type layer thickness. The counteraction leads to increased IQE and blue-shifted emission spectrum with increasing p-type thickness when the thickness is below a certain value (20-nm p-AlGaN plus 60-nm p-GaN under our growth conditions). Beyond this thickness, the IQE value decreases and the emission spectrum red shifts with increasing p-type thickness.

Hand-assisted laparoscopic versus total laparoscopic right colectomy: a randomized controlled trial.

AIM: Laparoscopic colectomy for colorectal cancer is associated with definite short-term benefits, and is increasingly practised worldwide. The limitations of a pure laparoscopic approach include a relative lack of tactile feedback and long procedural time. Hand-assisted laparoscopic surgery was introduced in an attempt to facilitate operation by improving the tactile sensation. To date, there is no consensus as to which approach is better. Herein we conducted a randomized controlled trial comparing hand-assisted laparoscopic colectomy (HALC) with total laparoscopic colectomy (TLC) in the management of right-sided colonic cancer. METHODS: Adult patients with carcinoma of the caecum and ascending colon were recruited and randomized to undergo either HALC or TLC. Measured outcomes included operative time, blood loss, conversion rate, postoperative morbidities, postoperative pain, length of hospital stay, disease recurrence and patient survival. RESULTS: Sixty patients (HALC=30, TLC=30) were recruited. The two groups were comparable with regard to age, gender distribution, body mass index and final histopathological staging. No difference was observed between the groups in terms of operating time, conversion rate, operative blood loss, pain score and length of hospital stay. With a median follow-up of 27 to 33 months, no difference was observed in terms of disease recurrence, and the 5-year survival rates remained similar (83%vs 80%, P=0.923). CONCLUSION: HALC is safe and feasible, but it does not show any significant benefits over TLC in terms of operating time and conversion rate. Routine use of the hand-assisted laparoscopic technique in right hemicolectomy is therefore not recommended.

Replication study of SNP associations for colorectal cancer in Hong Kong Chinese.

BACKGROUND: Recent genome-wide association studies of colorectal cancer (CRC) have identified common single-nucleotide polymorphisms (SNPs) mapping to 10 independent loci that confer modest increased risk. These studies have been conducted in European populations and it is unclear whether these observations generalise to populations with different ethnicities and rates of CRC. METHODS: An association study was performed on 892 CRC cases and 890 controls recruited from the Hong Kong Chinese population, genotyping 32 SNPs, which were either associated with CRC in previous studies or are in close proximity to previously reported risk SNPs. RESULTS: Twelve of the SNPs showed evidence of an association. The strongest associations were provided by rs10795668 on 10p14, rs4779584 on 15q14 and rs12953717 on 18q21.2. There was significant linear association between CRC risk and the number of independent risk variants possessed by an individual (P=2.29 × 10(-5)). CONCLUSION: These results indicate that some previously reported SNP associations also impact on CRC risk in the Chinese population. Possible reasons for failure of replication for some loci include inadequate study power, differences in allele frequency, linkage disequilibrium structure or effect size between populations. Our results suggest that many associations for CRC are likely to generalise across populations.

Laparoscopic sphincter-preserving total mesorectal excision: 10-year report.

AIM: Total mesorectal excision (TME) is currently the gold standard for resection of mid or low rectal cancer and is associated with a low local recurrence rate. However, few studies have reported the long-term oncological outcome following use of a laparoscopic approach. The aim of this study was to evaluate the long-term oncological outcome after laparoscopic sphincter-preserving TME with a median follow up of about 4 years. METHOD: Patients with mid or low rectal cancer who underwent laparoscopic sphincter-preserving TME with curative intent between March 1999 and March 2009 were prospectively recruited for analysis. RESULTS: During the 10-year study period, 177 patients underwent laparoscopic sphincter-preserving TME with curative intent for rectal cancer. Conversion was required in two (1%) patients. There was no operative mortality. At a median follow-up period of 49 months, local recurrence had occurred in nine (5.1%) patients. The overall metastatic recurrence rate after curative resection was 22%. The overall 5-year survival and 5-year disease-free survival in the present study were 74% and 71%, respectively. CONCLUSION: The results of this study show that laparoscopic sphincter-preserving TME is safe with long-term oncological outcomes comparable to those of open surgery.

The outcome of laparoscopic colorectal resection in T4 cancer.

AIM: Laparoscopic surgery for locally advanced tumours with extramural involvement is still controversial. It is believed that laparoscopic excision of T4 cancers is technically difficult and may result in prolonged operative time, increased conversion rate, added postoperative morbidity, and suboptimal oncological clearance. METHOD: Our unit has been practising laparoscopic colorectal surgery since 1992, and all data are entered into a database prospectively. Since 1999 we have routinely used the laparoscopic approach for colorectal cancer resections. Data regarding patients with a histologically T4 cancer operated on between 1999 and 2008 were analysed. Outcomes included operating time, conversion rate, postoperative complications and oncological outcome. RESULTS: Over a 10-year period, 146 patients (male 75) with a T4 cancer underwent laparoscopic resection. The median operating time was 125 (range, 46-285) min and the median blood loss was 50 (0-1800) ml. The conversion rate was 16%. Six (4.1%) patients experienced anastomotic leakage. The median number of lymph nodes harvested was 13 (2-40). One hundred and two (70%) patients underwent curative resection. The recurrence rates were 41% and 53% for stage II and III patients, respectively. Four (3.9%) patients had local recurrence. At a median follow up of 18 (1-118) months, the overall survival was 25 months, with median overall survival for patients with stage II, III and IV disease being 63, 36 and 12 months, respectively. CONCLUSION: Laparoscopic colectomy in histologically T4 cancer is safe. Oncological outcomes remain satisfactory. Based on our data, provided expertise is available, patients with locally advanced tumours should not be excluded from a laparoscopic approach.

Laparoscopic anterior resection.

Laparoscopic colectomy for cancer is increasingly practiced worldwide in the last 2 decades. However, due to procedural complexity, laparoscopic rectal cancer excision had not proceeded at a similar pace. This article deals with the technique of laparoscopic anterior resection. Resection of rectosigmoid or upper rectal tumors is first described, followed by the more difficult sphincter-saving total mesorectal excision. We have been using and modifying this technique of laparoscopic anterior resection for rectal cancer since 1990 s. In our recent review, the local recurrence rate was 7.4%, and the overall 5-year survival was 70%. Our data suggest laparoscopic resection for rectal cancer is safe and is the procedure of choice in selected patients.

Effect of endorectal coils on staging of rectal cancers by magnetic resonance imaging.

OBJECTIVE: To compare the use of endorectal plus phased-array coils with use of phased-array coil alone with respect to the accuracy of magnetic resonance imaging for detecting mesorectal involvement of rectal cancer. DESIGN: Retrospective study. SETTING: A tertiary referral centre in Hong Kong. PATIENTS: Ethnic Chinese patients with rectal adenocarcinoma who underwent staging magnetic resonance imaging during the years 2003 to 2008 in our centre were selected; those who received preoperative neoadjuvant therapy were excluded. Unless otherwise contra-indicated, endorectal coils have been used since 2006. MAIN OUTCOME MEASURES: Magnetic resonance images were retrieved and reviewed by two radiologists blinded to the pathological results. The radiological findings were then correlated with the pathological reports to determine diagnostic accuracy. RESULTS: A total of 50 patients were studied; 13 of the examinations were in patients having an endorectal coil. The overall accuracy of magnetic resonance imaging in detecting mesorectal tumour involvement was 80%. Subgroup analysis showed higher accuracy in the group with endorectal coils than in those with phased-array coils alone. Over-detection of mesorectal involvement was noted in 12% of the cases, with lower rate being observed in patients with endorectal coils. Underdetection of mesorectal tumour involvement was only noted in the group without endorectal coils. With the use of endorectal coils, the sensitivity reached 100% and the specificity increased to 86%. CONCLUSION: Use of endorectal coil in staging magnetic resonance imaging of the rectum improves diagnostic accuracy. Whenever feasible, endorectal coil use is therefore recommendable to enhance diagnostic accuracy. The study results substantiate the understanding of staging by magnetic resonance imaging of rectal cancer in the local Chinese population.

Laparoscopic rectal cancer surgery with and without neoadjuvant chemo-irradiation: a comparative study.

OBJECTIVES: To evaluate the perioperative short-term outcomes of laparoscopic rectal cancer surgery in patients after neoadjuvant chemo-irradiation. PATIENTS AND METHODS: This is a comparative cohort study designed to compare the perioperative and short-term outcomes of laparoscopic rectal cancer surgery in patients with and without neoadjuvant therapy. Patients undergoing elective laparoscopic rectal cancer surgery after neoadjuvant chemo-irradiation formed the study group; those receiving surgery without neoadjuvant therapy and in whom the final histology confirmed either transmural or node-positive diseases were selected as controls. RESULTS: Fifty-two patients in the neoadjuvant group were compared with 138 patients in the control group. Both groups were comparable in terms of American Society of Anesthesiologists (ASA) grading and gender distribution. Median operating time was significantly longer in the neoadjuvant group (155 versus 135 mins, p = 0.09, Mann-Whitney U test). No significant difference was observed in terms of blood loss, conversion rates, postoperative morbidity, length of hospital stay or sphincter preservation rates. Overall 5-year survival rates in the two groups remained similar. CONCLUSIONS: Our data confirmed that, aside from a slightly longer operating time, laparoscopic rectal cancer surgery in patients with neoadjuvant chemo-irradiation is safe with no increased morbidity. Based on our experience, patients after neoadjuvant therapy should not be deterred from the minimally invasive approach.

Endo-laparoscopic colectomy without mini-laparotomy for left-sided colonic tumors.

BACKGROUND: In performing "traditional" laparoscopic colectomy for left-sided colonic tumors, specimen retrieval necessitates a mini-laparotomy which often is the cause of postoperative pain, wound infection, and other pain-related complications. Here we describe a new technique of endo-laparoscopic anterior resection without mini-laparotomy, where specimen retrieval and colorectal anastomosis can be safely achieved with the use of the transanal endoscopic operation (TEO) device set-up. METHODS: This hybrid natural orifice transluminal endoscopic surgery (NOTES) technique involves insertion of the TEO device in the lower rectum and luminal extraction of the specimen via the device. The technique is applicable to patients with small tumors (4 cm or less) in the left-sided colon or upper rectum, where transanal construction of a stapled colorectal anastomosis is intended. RESULTS: The technique was attempted in ten patients (male:female 4:6) with median age of 66 years (range: 55-81 years). Five patients suffered from rectosigmoid tumors, whereas four patients had lesions in the sigmoid colon and one had a lesion in the descending colon. The median operating time was 127.5 min (range: 105-170 min) and the median blood loss was 20 ml (range: 20-50 ml). The median hospital stay was 7 days (range: 4-18 days), while the median maximum pain score (visual analog score) was 2 (range: 2-3) during in-hospital stay in this small series. CONCLUSIONS: Our preliminary experience indicates this new technique of endo-laparoscopic colectomy is feasible for selected patients with left-sided colonic tumors. Complications related to mini-laparotomy can be abolished entirely with this hybrid approach.

Colonic injury from electric arcing: a significant complication of argon plasma coagulation.

Argon plasma coagulation is increasingly used in endoscopic haemostasis. This case report illustrates the potential for thermal injury at a staple line remote from the area of argon plasma coagulation treatment as a result of electrical arcing. Increasing numbers of colorectal anastomosis and reconstruction procedures are now being performed using stapling techniques and the use of argon plasma coagulation in these patients has become a common situation in clinical practice. Information about this potential danger should be well disseminated to endoscopists and surgeons to avoid preventable complications. The presence of a staple line nearby should be considered a contra-indication for argon plasma coagulation.

Obstructive complications of laparoscopically created defunctioning ileostomy.

PURPOSE: The use of defunctioning ileostomy is a common practice to reduce the septic complications after anastomotic leakage in colorectal surgery. In open surgery, the fashioning of ileostomy is a straightforward procedure. However, in the laparoscopic approach, this can be a difficult task and obstructive complications can occur postoperatively. METHODS: A retrospective review was undertaken for all patients who underwent laparoscopic colorectal resection and defunctioning loop ileostomy over a 15-year period. RESULTS: In this period, 161 patients underwent laparoscopic colorectal surgery with defunctioning ileostomy. Eight patients developed obstructive complications in the early postoperative period requiring surgical intervention (5 percent). All patients presented with intestinal obstruction from the fourth to the sixth postoperative day. The median time to reoperation was 9.5 days (range, 5 to 19). The causes of obstructive complications were twisting of the ileostomy (n = 3), adhesive kinking proximal to the ileostomy (n = 3), tight fascia (n = 1), and both tight fascia and twisting of ileostomy (n = 1). Six patients underwent laparotomy for diagnosis and refashioning of ileostomy. The seventh patient had endoscopic decompression of small bowel and refashioning of ileostomy. The last patient was successfully managed with combined endoscopic and laparoscopic approach. CONCLUSIONS: Various pitfalls can occur in laparoscopically created defunctioning ileostomy. Measures can be taken to minimize these technical errors. Various surgical reinterventions can be attempted to determine the cause. With combined uses of enteroscope and laparoscope, a laparotomy can be avoided.

A comparison of left and right atrial fibroblasts reveals different collagen production activity and stress-induced mitogen-activated protein kinase signalling in rats.

AIM: Atrial fibrosis plays a pivotal role in the pathophysiology of heart failure (HF). The left atrium (LA) experiences greater fibrosis than the right atrium (RA) during HF. It is not clear whether LA cardiac fibroblasts contain distinctive activities that predispose LA to fibrosis. METHODS: LA and RA fibrosis were evaluated in healthy and isoproterenol-induced HF Sprague Dawley rats. Rat LA and RA primary isolated fibroblasts were subjected to proliferation assay, oxidative stress assay, cell migration analysis, collagen measurement, cytokine array and Western blot. RESULTS: Healthy rat LA and RA had a similar extent of collagen deposition. HF significantly increased fibrosis to a greater severity in LA than in RA. Compared to isolated RA fibroblasts, the in vitro experiments showed that isolated LA fibroblasts had higher oxidative stress and exhibited higher collagen, transforming growth factor-ß1, connective tissue growth factor production and less vascular endothelial growth factor (VEGF) production, but had similar migration, myofibroblast differentiation and proliferation activities. VEGF significantly increased the collagen production ability of LA fibroblasts, but not RA fibroblasts. LA fibroblasts had more phosphorylated ERK1/2 and P38 expression. ERK inhibitor (PD98059, 50 µmol L-1 ) significantly attenuated collagen production and increased VEGF production in RA fibroblasts but not in LA fibroblasts. P38 inhibitor (SB203580, 30 µmol L-1 ) significantly attenuated collagen production in LA fibroblasts but not in RA fibroblasts. P38 inhibitor also significantly increased VEGF production in RA and LA fibroblasts. CONCLUSIONS: Differences in profibrotic activity between LA and RA fibroblasts may be caused by different responses to mitogen-activated protein kinase signalling.

Endo-Lap OR: an innovative "minimally invasive operating room" design.

BACKGROUND: A newly constructed Endoscopic-Laparoscopic operating room (Endo-Lap OR) started to operate in our department in January 2005. A prospective study was conducted to evaluate its feasibility, efficacy, and safety, as well as the staff's satisfaction. PATIENTS AND METHODS: From January 2005 to September 2005, all patients undergoing operation in this Endo-Lap OR were included in the study. The patient's diagnosis, types of operating procedures, incidents of operating failure (either due to the hardware or the software of Endo-Lap OR) that led to a delay in the patient's transfer or that extended the total operating time were recorded. In addition, questionnaires regarding staff satisfaction with the new operating room were distributed to nurses, anesthetists, and surgeons. RESULTS: A total of 640 cases were included in the study period, 245 cases of open surgery, 282 cases of laparoscopic surgery, 82 cases of endoscopic surgery, 17 cases of video-assisted thoracoscopic surgery, and 14 cases of combined endoscopic-laparoscopic surgery. There were no reported incidents of operating failure related to hardware or software problems. The overall staff satisfaction was excellent. CONCLUSIONS: The integration of endoscopic and laparoscopic surgery into this newly constructed Endo-Lap OR is feasible and safe. The running of the operating room was smooth and it received a high level of acceptance and satisfaction from different staff members.

Colonic amoebic abscess mimicking carcinoma of the colon.

Amoebiasis is an uncommon disease in developed countries. Its clinical presentation can be variable and non-specific, and the diagnosis can be easily overlooked. We report a case of colonic amoebic abscess mimicking advanced colonic cancer with acute intestinal obstruction and liver metastasis. The presentation, diagnosis, and treatment of amoebiasis are also reviewed.

Minimally invasive surgery for rectal cancer.

The present scarcity of literature on laparoscopic rectal cancer surgery makes it premature to determine whether laparoscopic surgery should be the standard of care for rectal cancer. Notwithstanding that, the available evidence proves its safety and adequate oncological clearance. Moreover, current data do not suggest any detrimental effect on the postoperative and early oncological outcomes. On the contrary, there is level three evidence showing that laparoscopic technique results in less blood loss, shorter length of stay, and reduced abdominal wound disorders and pulmonary complications, albeit the overall morbidity remains similar to that of open surgery. Long-term survival outcomes remain largely unclear, however. Hence, it is high time that laparoscopic technique should be further evaluated, preferably by means of large-scale randomized trials, to define its exact role in the treatment of rectal cancer.