Pushdown Automata Correspond to Context Free Grammars

One of the standard proofs about pushdown automata and context free grammars is that both correspond to the context free languages. The proof is typically in two parts, one showing that for every context free grammar there is a corresponding pushdown automaton, and the other showing that for every pushdown automaton there is a corresponding context free grammar. This resource provides the latter proof for Maheshwari and Smid\u27s pushdown automata

Surface Reconstruction from Constructive Solid Geometry for Interactive Visualization

A method is presented for constructing a set of triangles that closely approximates the surface of a constructive solid geometry model. The method subdivides an initial triangulation of the model’s primitives into triangles that can be classified accurately as either on or off of the surface of the whole model, and then recombines these small triangles into larger ones that are still either entirely on or entirely off the surface. Subdivision and recombination can be done in a preprocessing step, allowing later rendering of the triangles on the surface (i.e., the triangles visible from outside the model) to proceed at interactive rates. Performance measurements confirm that this method achieves interactive rendering speeds. This approach has been used with good results in an interactive scientific visualization program

Is Computer Science a Relevant Academic Discipline for the 21st Century

The current view of computing as technology overlooks the discipline’s theoretical and scientific foundations in computer science, weakening the entire computing enterprise

Post-treatment survival difference between lobectomy and stereotactic ablative radiotherapy in stage I non-small cell lung cancer in England.

BACKGROUND: Approximately 15%-20% of all non-small cell lung cancer (NSCLC) cases present with stage I disease. Surgical resection traditionally offers the best chance of a cure but some patients will not have this treatment due to older age, comorbidities or personal choice. Stereotactic ablative radiotherapy (SABR) has become an established curative intent treatment option for patients who are not selected for or do not choose surgery. The aim of this study is to compare survival at 90 days, 6 months, 1 year and 2 years for patients who received either lobectomy or SABR. METHODS: We used data from the 2015 National Lung Cancer Audit database and linked with Hospital Episode Statistics and the radiotherapy dataset to identify patients with NSCLC stage IA-IB and performance status (PS) 0-2 who underwent surgery or SABR treatment. We assessed the likelihood of death at 90 days, 6 months, 1 year and 2 year after diagnosis and procedure date to observe survival between two patient groups. RESULTS: We identified 2373 patients in our cohort, 476 of whom had SABR. The median difference between date of diagnosis and date of treatment for surgery patients was 17 days while for SABR patients it was 73 days. Increasing age and worsening PS were associated with having SABR rather than surgery. Survival between the two treatment modalities was similar early on but by 1-year people who had surgery did better than those who had SABR (adjusted ORs 2.12, 95% CI 1.35 to 2.31). This difference persisted at 2 years and when the analysis was restricted to patients aged <80 years and with PS 0 or 1 and stage IA only. CONCLUSION: Our analysis suggests that patients who have lobectomy have a better survival compared with SABR patients; however, we found considerable delays in patients receiving SABR which may contribute to poorer long-term outcomes with this treatment option. Reducing these delays should be a key focus in development and reorganisation of services

Apparent Alkyl Transfer and Phenazine Formation via an Aryne Intermediate

Treatment of chlorotriaryl derivatives 3a and 3d or fluorotriaryl derivatives 3b and 3e with potassium diisopropylamide afforded alkyl-shifted phenazine derivatives 5a/5b, rather than the expected 9-membered triazaorthocyclophane 2a. The phenazine derivatives were isolated in 78–98% yield depending on the halogen and alkyl group present. In the absence of the halogen (chloro or fluoro), the apparent alkyl shift proceeds more slowly and cannot proceed via the intermediacy of the aryne intermediate. Mechanistic possibilities include intramolecular nucleophilic attack on an aryne intermediate leading to a zwitterionic intermediate and alkyl transfer via a 5-endo-tet process, or via a Smiles rearrangement

Expert consensus and recommendations on safety criteria for active mobilization of mechanically ventilated critically ill adults

Introduction: The aim of this study was to develop consensus recommendations on safety parameters for mobilizing adult, mechanically ventilated, intensive care unit (ICU) patients. Methods: A systematic literature review was followed by a meeting of 23 multidisciplinary ICU experts to seek consensus regarding the safe mobilization of mechanically ventilated patients. Results: Safety considerations were summarized in four categories: respiratory, cardiovascular, neurological and other. Consensus was achieved on all criteria for safe mobilization, with the exception being levels of vasoactive agents. Intubation via an endotracheal tube was not a contraindication to early mobilization and a fraction of inspired oxygen less than 0.6 with a percutaneous oxygen saturation more than 90% and a respiratory rate less than 30 breaths/minute were considered safe criteria for in- and out-of-bed mobilization if there were no other contraindications. At an international meeting, 94 multidisciplinary ICU clinicians concurred with the proposed recommendations. Conclusion: Consensus recommendations regarding safety criteria for mobilization of adult, mechanically ventilated patients in the ICU have the potential to guide ICU rehabilitation whilst minimizing the risk of adverse events