Ten-dimensional wave packet simulations of methane scattering

We present results of wavepacket simulations of scattering of an oriented methane molecule from a flat surface including all nine internal vibrations. At a translational energy up to 96 kJ/mol we find that the scattering is almost completely elastic. Vibrational excitations when the molecule hits the surface and the corresponding deformation depend on generic features of the potential energy surface. In particular, our simulation indicate that for methane to dissociate the interaction of the molecule with the surface should lead to an elongated equilibrium C--H bond length close to the surface.Comment: RevTeX 15 pages, 3 eps figures: This article may be found at http://link.aip.org/link/?jcp/109/1966

Minimally invasive total mesorectal excision:assessing the surgical treatment of rectal carcinoma

The treatment of rectal carcinoma consists of (chemo)radiotherapy and the surgical resection of the tumor, including its surrounding fat tissue and lymph nodes: total mesorectal excision (TME). The surgical resection has evolved significantly over the last twenty years: Initially, open abdominal surgery was necessary, but after the introduction of the laparoscopic technique, this has become the standard (laparoscopic TME). Subsequently, robot-assisted abdominal surgery (robot-assisted TME), and transanal excision of the tumor (TaTME) were introduced. This thesis aims to compare outcomes between the following three minimally invasive techniques for the surgical resection of rectal carcinoma: laparoscopic TME (L-TME), robot-assisted TME (R-TME) and transanal TME (TaTME). The initial period (learning curve) of the minimally invasive technique was not found to be associated with an increase in complications or survival. However, an increase in complications and local recurrence has been found in papers reporting on L-TME and TaTME during the learning curve. This could be due to the technological advances of the robot-assisted technique, or because L-TME and TaTME differ significantly from the preceding resection technique, while R-TME is quite similar to the preceding resection technique. After the learning curve has been reached, outcomes do not differ significantly regarding complications and survival. However, L-TME is found to be associated with an increase in stoma construction, and an increase in periprocedural changes of the operative plan in low rectal tumors. TaTME and R-TME might therefore be a better technique for the excision of technically difficult low rectal tumors. More research should aim to elucidate whether a reduction in stoma construction in the R-TME and TaTME leads to an increase in quality of life, and whether the additional costs of these techniques outweigh the potential gain in quality of life

Energy distribution analysis of the wavepacket simulations of CH4 and CD4 scattering

The isotope effect in the scattering of methane is studied by wavepacket simulations of oriented CH4 and CD4 molecules from a flat surface including all nine internal vibrations. At a translational energy up to 96 kJ/mol we find that the scattering is still predominantly elastic, but less so for CD4. Energy distribution analysis of the kinetic energy per mode and the potential energy surface terms, when the molecule hits the surface, are used in combination with vibrational excitations and the corresponding deformation. They indicate that the orientation with three bonds pointing towards the surface is mostly responsible for the isotope effect in the methane dissociation.Comment: 20 pages LaTeX, 1 figure (eps), to be published in Surf. Sc

Electronic structure calculations and dynamics of methane activation on nickel and cobalt

The dissociative chemisorption of CH4 on nickel and cobalt has been studied using different cluster models. D. functional theory is used to det. the structure and potential energy surface in the reactant-, transition state-, and product region. The transition state is explicitly detd. on a single atom, a one layer 7-atom cluster and a spherical 13-atom cluster. We find transition state barriers of 41 kJ/mol for a single nickel atom, 79 kJ/mol for a single cobalt atom, 214 kJ/mol for the Ni7-cluster, 216 kJ/mol for the Co7-cluster, 121 kJ/mol for the Ni13-cluster, and 110 kJ/mol for the Co13-cluster. The overall reaction energies are -34, 6, 142, 135, 30, and 8 kJ/mol, resp. The higher barrier for the single cobalt atom in comparison with the nickel atom can be attributed to the difference between both atoms in the occupation of the s-orbital in the lowest lying states. The higher and almost the same barrier for the 7-atom clusters can be attributed to the intrinsic lower reactivity of the central atom embedded in the cluster and the similar electronic nature of the atoms in the clusters; in both clusters the atoms have open s- and d-shells. The lower barrier for the 13-atom clusters compared with the 7-atom clusters is a result of each surface atom now having 5 bonds, which gives a more balanced description of the substrate model. [on SciFinder (R)

Implications of the new MRI-based rectum definition according to the sigmoid take-off:multicentre cohort study

Background: The introduction of the sigmoid take-off definition might lead to a shift from rectal cancers to sigmoid cancers. The aim of this retrospective cohort study was to determine the clinical impact of the new definition. Methods: In this multicentre retrospective cohort study, patients were included if they underwent an elective, curative total mesorectal excision for non-metastasized rectal cancer between January 2015 and December 2017, were registered in the Dutch Colorectal Audit as having a rectal cancer according to the previous definition, and if MRI was available. All selected rectal cancer cases were reassessed using the sigmoid take-off definition. The primary outcome was the number of patients reassessed with a sigmoid cancer. Secondary outcomes included differences between the newly defined rectal and sigmoid cancer patients in treatment, perioperative results, and 3-year oncological outcomes (overall and disease-free survivals, and local and systemic recurrences). Results: Out of 1742 eligible patients, 1302 rectal cancer patients were included. Of these, 170 (13.1 per cent) were reclassified as having sigmoid cancer. Among these, 93 patients (54.7 per cent) would have been offered another adjuvant or neoadjuvant treatment according to the Dutch guideline. Patients with a sigmoid tumour after reassessment had a lower 30-day postoperative complication rate (33.5 versus 48.3 per cent, P &lt; 0.001), lower reintervention rate (8.8 versus 17.4 per cent, P &lt; 0.007), and a shorter length of stay (a median of 5 days (i.q.r. 4-7) versus a median of 6 days (i.q.r. 5-9), P &lt; 0.001). Three-year oncological outcomes were comparable. Conclusion: Using the anatomical landmark of the sigmoid take-off, 13.1 per cent of the previously classified patients with rectal cancer had sigmoid cancer, and 54.7 per cent of these patients would have been treated differently with regard to neoadjuvant therapy or adjuvant therapy.</p

Implications of the new MRI-based rectum definition according to the sigmoid take-off:multicentre cohort study

Background: The introduction of the sigmoid take-off definition might lead to a shift from rectal cancers to sigmoid cancers. The aim of this retrospective cohort study was to determine the clinical impact of the new definition. Methods: In this multicentre retrospective cohort study, patients were included if they underwent an elective, curative total mesorectal excision for non-metastasized rectal cancer between January 2015 and December 2017, were registered in the Dutch Colorectal Audit as having a rectal cancer according to the previous definition, and if MRI was available. All selected rectal cancer cases were reassessed using the sigmoid take-off definition. The primary outcome was the number of patients reassessed with a sigmoid cancer. Secondary outcomes included differences between the newly defined rectal and sigmoid cancer patients in treatment, perioperative results, and 3-year oncological outcomes (overall and disease-free survivals, and local and systemic recurrences). Results: Out of 1742 eligible patients, 1302 rectal cancer patients were included. Of these, 170 (13.1 per cent) were reclassified as having sigmoid cancer. Among these, 93 patients (54.7 per cent) would have been offered another adjuvant or neoadjuvant treatment according to the Dutch guideline. Patients with a sigmoid tumour after reassessment had a lower 30-day postoperative complication rate (33.5 versus 48.3 per cent, P &lt; 0.001), lower reintervention rate (8.8 versus 17.4 per cent, P &lt; 0.007), and a shorter length of stay (a median of 5 days (i.q.r. 4-7) versus a median of 6 days (i.q.r. 5-9), P &lt; 0.001). Three-year oncological outcomes were comparable. Conclusion: Using the anatomical landmark of the sigmoid take-off, 13.1 per cent of the previously classified patients with rectal cancer had sigmoid cancer, and 54.7 per cent of these patients would have been treated differently with regard to neoadjuvant therapy or adjuvant therapy.</p

The learning curve of laparoscopic, robot-assisted and transanal total mesorectal excisions:a systematic review

Background The standard treatment of rectal carcinoma is surgical resection according to the total mesorectal excision principle, either by open, laparoscopic, robot-assisted or transanal technique. No clear consensus exists regarding the length of the learning curve for the minimal invasive techniques. This systematic review aims to provide an overview of the current literature regarding the learning curve of minimal invasive TME. Methods A systematic literature search was performed. PubMed, Embase and Cochrane Library were searched for studies with the primary or secondary aim to assess the learning curve of either laparoscopic, robot-assisted or transanal TME for rectal cancer. The primary outcome was length of the learning curve per minimal invasive technique. Descriptive statistics were used to present results and the MINORS tool was used to assess risk of bias. Results 45 studies, with 7562 patients, were included in this systematic review. Length of the learning curve based on intraoperative complications, postoperative complications, pathological outcomes, or a composite endpoint using a risk-adjusted CUSUM analysis was 50 procedures for the laparoscopic technique, 32-75 procedures for the robot-assisted technique and 36-54 procedures for the transanal technique. Due to the low quality of studies and a high level of heterogeneity a meta-analysis could not be performed. Heterogeneity was caused by patient-related factors, surgeon-related factors and differences in statistical methods. Conclusion Current high-quality literature regarding length of the learning curve of minimal invasive TME techniques is scarce. Available literature suggests equal lengths of the learning curves of laparoscopic, robot-assisted and transanal TME. Well-designed studies, using adequate statistical methods are required to properly assess the learning curve, while taking into account patient-related and surgeon-related factors

Prospective multicentre observational cohort to assess quality of life, functional outcomes and cost-effectiveness following minimally invasive surgical techniques for rectal cancer in 'dedicated centres' in the Netherlands (VANTAGE trial):A protocol

Introduction: Total mesorectal excision is the standard of care for rectal cancer, which can be performed using open, laparoscopic, robot-assisted and transanal technique. Large prospective (randomised controlled) trials comparing these techniques are lacking, do not take into account the learning curve and have short-term or long-term oncological results as their primary endpoint, without addressing quality of life, functional outcomes and cost-effectiveness. Comparative data with regard to these outcomes are necessary to identify the optimal minimally invasive technique and provide guidelines for clinical application. Methods and analysis: This trial will be a prospective observational multicentre cohort trial, aiming to compare laparoscopic, robot-assisted and transanal total mesorectal excision in adult patients with rectal cancer performed by experienced surgeons in dedicated centres. Data collection will be performed in collaboration with the prospective Dutch ColoRectal Audit and the Prospective Dutch ColoRectal Cancer Cohort. Quality of life at 1 year postoperatively will be the primary outcome. Functional outcomes, cost-effectiveness, short-term outcomes and long-term oncological outcomes will be the secondary outcomes. In total, 1200 patients will be enrolled over a period of 2 years in 26 dedicated centres in the Netherlands. The study is registered at https://www.trialregister.nl/9734 (NL9734). Ethics and dissemination: Data will be collected through collaborating parties, who already obtained approval by their medical ethical committee. Participants will be included in the trial after having signed informed consent. Results of this study will be disseminated to participating centres, patient organisations, (inter)national society meetings and peer-reviewed journals