179 research outputs found
A combinatorial method to find sharp lower bounds on flip distances
No full textInternational audienceConsider the triangulations of a convex polygon with vertices. In 1988, Daniel Sleator, Robert Tarjan, and William Thurston have shown that the flip distance of two such triangulations is at most when is greater than 12 and that this bound is sharp when is large enough. They also conjecture that `"large enough'' means greater than 12. A proof of this conjecture was recently announced by the author. A sketch of this proof is given here, with emphasis on the intuitions underlying the construction of lower bounds on the flip distance of two triangulations.En 1988, Daniel Sleator, Robert Tarjan et William Thurston ont montré que la distance, en nombre de flips, de deux triangulations d’un polygone convexe de sommets est au plus quand est supérieur à 12. Ils ont également montré que cette borne est atteinte si est suffisamment grand et ils conjecturent qu’il existe deux triangulations à distance dès que est supérieur à 12. Une preuve de cette conjecture a récemment été proposée par l’auteur. Une ébauche de cette preuve est présentée ici qui explique de manière intuitive les méthodes permettant d’obtenir des bornes inférieures sur la distance, en nombre de flips, de deux triangulations
Shortest Path Separators in Unit Disk Graphs
No full textWe introduce a new balanced separator theorem for unit-disk graphs involving two shortest paths combined with the 1-hop neighbours of those paths and two other vertices. This answers an open problem of Yan, Xiang and Dragan [CGTA '12] and improves their result that requires removing the 3-hop neighbourhood of two shortest paths. Our proof uses very different ideas, including Delaunay triangulations and a generalization of the celebrated balanced separator theorem of Lipton and Tarjan [J. Appl. Math. '79] to systems of non-intersecting paths
The induced path function, monotonicity and betweenness
No full textThe induced path function of a graph consists of the set of all vertices lying on the induced paths between vertices and . This function is a special instance of a transit function. The function satisfies betweenness if implies and implies , and it is monotone if implies . The induced path function of aconnected graph satisfying the betweenness and monotone axioms are characterized by transit axioms.betweenness;induced path;transit function;monotone;house domino;long cycle;p-graph
Tree Buffers
No full textIn runtime verification, the central problem is to decide if a given program execution violates a given property. In online runtime verification, a monitor observes a program’s execution as it happens. If the program being observed has hard real-time constraints, then the monitor inherits them. In the presence of hard real-time constraints it becomes a challenge to maintain enough information to produce error traces, should a property violation be observed. In this paper we introduce a data structure, called tree buffer, that solves this problem in the context of automata-based monitors: If the monitor itself respects hard real-time constraints, then enriching it by tree buffers makes it possible to provide error traces, which are essential for diagnosing defects. We show that tree buffers are also useful in other application domains. For example, they can be used to implement functionality of capturing groups in regular expressions. We prove optimal asymptotic bounds for our data structure, and validate them using empirical data from two sources: regular expression searching through Wikipedia, and runtime verification of execution traces obtained from the DaCapo test suite
Limits on Computationally Efficient VCG-Based Mechanisms for Combinatorial Auctions and Public Projects
No full textA natural goal in designing mechanisms for auctions and public projects is to maximize the social welfare while incentivizing players to bid truthfully. If these are the only concerns, the problem is easily solved by use of the VCG mechanism. Unfortunately, this mechanism is not computationally efficient in general and there are currently no other general methods for designing truthful mechanisms. However, it is possible to design computationally efficient VCG-based mechanisms which approximately maximize the social welfare.
We explore the design space of computationally efficient VCG-based mechanisms under submodular valuations and show that the achievable approximation guarantees are poor, even compared to efficient non-truthful algorithms. Some of these approximation hardness results stem from an asymmetry in the information available to the players versus that available to the mechanism. We develop an alternative Instance Oracle model which reduces this asymmetry by allowing the mechanism to access some computational capabilities of the players. By building assumptions about player computation into the model, a more realistic study of mechanism design can be undertaken.
Finally, we give VCG-based mechanisms for some problems in the Instance Oracle model which achieve provably better approximations than the best VCG-based mechanism in the standard model. However, for other problems we give reductions in the Instance Oracle model which prove inapproximability results as strong as those shown in the standard model. These provide more robust hardness results that are not simply artifacts of the asymmetry in the standard model.</p
Reduced costs with bisoprolol treatment for heart failure - An economic analysis of the second Cardiac Insufficiency Bisoprolol Study (CIBIS-II)
No full textBackground
Beta-blockers, used as an adjunctive to diuretics, digoxin and angiotensin converting enzyme inhibitors, improve survival in chronic heart failure. We report a prospectively planned economic analysis of the cost of adjunctive beta-blocker therapy in the second Cardiac Insufficiency BIsoprolol Study (CIBIS II).
Methods
Resource utilization data (drug therapy, number of hospital admissions, length of hospital stay, ward type) were collected prospectively in all patients in CIBIS . These data were used to determine the additional direct costs incurred, and savings made, with bisoprolol therapy. As well as the cost of the drug, additional costs related to bisoprolol therapy were added to cover the supervision of treatment initiation and titration (four outpatient clinic/office visits). Per them (hospital bed day) costings were carried out for France, Germany and the U.K. Diagnosis related group costings were performed for France and the U.K. Our analyses took the perspective of a third party payer in France and Germany and the National Health Service in the U.K.
Results
Overall, fewer patients were hospitalized in the bisoprolol group, there were fewer hospital admissions perpatient hospitalized, fewer hospital admissions overall, fewer days spent in hospital and fewer days spent in the most expensive type of ward. As a consequence the cost of care in the bisoprolol group was 5-10% less in all three countries, in the per them analysis, even taking into account the cost of bisoprolol and the extra initiation/up-titration visits. The cost per patient treated in the placebo and bisoprolol groups was FF35 009 vs FF31 762 in France, DM11 563 vs DM10 784 in Germany and pound 4987 vs pound 4722 in the U.K. The diagnosis related group analysis gave similar results.
Interpretation
Not only did bisoprolol increase survival and reduce hospital admissions in CIBIS II, it also cut the cost of care in so doing. This `win-win' situation of positive health benefits associated with cost savings is Favourable from the point of view of both the patient and health care systems. These findings add further support for the use of beta-blockers in chronic heart failure
Improved differentiation between ductal and acinar prostate cancer using three-dimensional histology and biomarkers
No full textObjective. The aim of the study was to refine the methodology for discriminating the ductal (DAP) and acinar adenocarcinomas (AAP) of the prostate and confirm that prostate carcinoma of ductal origin is a more aggressive subtype. Material and methods. A retrospective analysis of 110 consecutive radical prostatectomy cases operated on between 2000 and 2006 and worked up using large-format "two-dimensional" (2D; 4 mu m thick) and "three-dimensional" (3D; 1500 mu m thick) histology sections was carried out, with an average follow-up of 5.1 years. The same material was also analysed for selected biomarkers in tissue microarray blocks. The most discriminatory biomarkers were then tested on preoperative core biopsy specimens from 24 of these patients. Results. 3D histology classified 97/110 (88%) cases of AAP and 13/110 (12%) DAP, which was then confirmed in 2D specimens. The DAP cases had a significantly greater frequency of pT3a and more advanced cancers, > 20 mm tumour focus, high-grade prostatic intraepithelial neoplasia, Gleason score >= 7, positive margin, extracapsular extension, vascular invasion, seminal vesicle infiltration, biochemical/local recurrence, regional lymph-node metastases and distant metastases. Three biomarkers in combination (chromogranin A, epidermal growth factor receptor and p53] distinguished DAP from AAP with an accuracy of 94% (area under the curve 0.94, 95% confidence interval 0.88-0.99). The same high accuracy was achieved using these three biomarkers on the preoperative specimens. Conclusions. Both 3D histology and the three selected biomarkers can help in accurately distinguishing DAP from AAP. The clear-cut distinction of two forms of prostate cancers by the approach advocated in this paper would allow AAP patients to undergo less radical treatment and would segregate DAP patients into a subset requiring more effective treatment regimens
A Comparison of Gait Kinetics between Prosthetic Feet during Functional Activities - Symmetry in External Work Approach
No full textBackground: Unilateral transtibial amputees (TTAs) show subtle gait variations while using different prosthetic feet. These variations have not been detected consistently with previous experimental measures. In this research project a novel measure for quantifying kinetic gait differences among prosthetic feet, called Symmetry in External Work (SEW), was introduced. The reliability of the SEW measure was calculated and its correlation with selected clinical measures was determined. The SEW measure was then applied to determine gait differences among four categories of prosthetic feet during various functional activities. Methodology: The study was conducted in three phases. Phase I was a single subject Pilot study to determine the sensitivity of the SEW measure to different prosthetic feet and functional activities. In Phase II, test-retest reliability of the SEW measure was determined for 5 TTAs during the functional activities of level walking, incline walking, decline walking, ascending stairs, descending stairs, sit-to-stand and stand-to-sit. The agreement between SEW values obtained from F-scan and force plates was also calculated. In Phase III, 11 subjects underwent 6 testing sessions over a period of 10-12 weeks. In session 1 subjects were tested wearing their existing prostheses (Baseline session), were given specialized prosthetic training and were tested again after 2 weeks (Training session). For sessions 3 through session 6, subjects were tested with a study socket and one of four randomized test feet. The test feet were SACH, SAFE, Talux and Proprio foot, classified as K1_foot, K2_foot, K3_foot and MP_foot, based on Medicare Functional Classification Level. The Step Watch Activity Monitor (SAM) recorded their daily activities in the 10-14 day accommodation period between two sessions. At each testing session, subjects completed the Prosthesis Evaluation Questionnaire (PEQ-13) and Usability questionnaire, and were evaluated using the Amputee Mobility Predictor (AMP) and the 6-minute walk test (6MWT). Ground reaction forces were collected using F-scan in-sole sensors as subjects performed the above mentioned functional activities. SEW values between the intact limb and the prosthetic limb were computed by integrating vertical ground reaction forces. Intra-class Correlation Coefficients (ICCs) were calculated to determine test-retest reliability and a repeated measure ANOVA was used to establish differences between the prosthetic feet. Results: The ICC values for Test-Retest reliability ranged from 0.84-0.94 for the various functional activities. There was moderate agreement between the SEW values calculated with F-scan and force plates. The SEW values were significantly different between the K3_foot and other feet during level walking and decline walking. During stair ascent, the MP_foot had a significantly higher SEW value than the other feet. There were no differences between feet during incline walking and stair descent. Training resulted in a significant improvement in symmetry from the Baseline session during sit-to-stand, while for stand-to-sit there were no differences between sessions. The PEQ-13 score was not different between sessions, while the Usability scores were significantly different between the K3_foot/MP_foot and K1_foot/K2_foot. The AMP score had a significant increase following Training while the 6MWT score showed a significant increase in the distance walked with the K1_foot, K3_foot and MP_foot over Baseline. The output of SAM did not show any difference in the number of steps or activity level of subjects. There was good to excellent correlation between the SEW values for level walking and other clinical outcome measures. Discussion and Conclusion: The SEW measure had excellent test-retest reliability and the agreement between the F-scan and force plates values could not be established because of a small sample size. The variations in SEW values were the result of distinctive designs of prosthetic feet. The high SEW value of the K3_foot can be attributed to its heel-toe foot plate and "J" shaped ankle spring design, which allowed for greater late stance stability. The active dorsiflexion feature of the MP_foot caused a change in strategy, typically used during stair ascent, resulting in a greater inter-limb symmetry. The SEW measure is a viable method to detect kinetic gait differences among prosthetic feet and represents a resource-effective alternative to traditional gait laboratories. It has several advantages and with further development of in-sole sensor technology, the potential for clinical use due to its relatively low cost instrumentation and minimal subject intervention.</p
An oil pipeline design problem
No full textCopyright @ 2003 INFORMSWe consider a given set of offshore platforms and onshore wells producing known (or estimated) amounts of oil to be connected to a port. Connections may take place directly between platforms, well sites, and the port, or may go through connection points at given locations. The configuration of the network and sizes of pipes used must be chosen to minimize construction costs. This problem is expressed as a mixed-integer program, and solved both heuristically by Tabu Search and Variable Neighborhood Search methods and exactly by a branch-and-bound method. Two new types of valid inequalities are introduced. Tests are made with data from the South Gabon oil field and randomly generated problems.The work of the first author was supported by NSERC grant #OGP205041. The work of the second author was supported by FCAR (Fonds pour la Formation des Chercheurs et l’Aide à la Recherche) grant #95-ER-1048, and NSERC grant #GP0105574
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A Comparison of Gait Kinetics between Prosthetic Feet during Functional Activities - Symmetry in External Work Approach
No full textBackground: Unilateral transtibial amputees (TTAs) show subtle gait variations while using different prosthetic feet. These variations have not been detected consistently with previous experimental measures. In this research project a novel measure for quantifying kinetic gait differences among prosthetic feet, called Symmetry in External Work (SEW), was introduced. The reliability of the SEW measure was calculated and its correlation with selected clinical measures was determined. The SEW measure was then applied to determine gait differences among four categories of prosthetic feet during various functional activities. Methodology: The study was conducted in three phases. Phase I was a single subject Pilot study to determine the sensitivity of the SEW measure to different prosthetic feet and functional activities. In Phase II, test-retest reliability of the SEW measure was determined for 5 TTAs during the functional activities of level walking, incline walking, decline walking, ascending stairs, descending stairs, sit-to-stand and stand-to-sit. The agreement between SEW values obtained from F-scan and force plates was also calculated. In Phase III, 11 subjects underwent 6 testing sessions over a period of 10-12 weeks. In session 1 subjects were tested wearing their existing prostheses (Baseline session), were given specialized prosthetic training and were tested again after 2 weeks (Training session). For sessions 3 through session 6, subjects were tested with a study socket and one of four randomized test feet. The test feet were SACH, SAFE, Talux and Proprio foot, classified as K1_foot, K2_foot, K3_foot and MP_foot, based on Medicare Functional Classification Level. The Step Watch Activity Monitor (SAM) recorded their daily activities in the 10-14 day accommodation period between two sessions. At each testing session, subjects completed the Prosthesis Evaluation Questionnaire (PEQ-13) and Usability questionnaire, and were evaluated using the Amputee Mobility Predictor (AMP) and the 6-minute walk test (6MWT). Ground reaction forces were collected using F-scan in-sole sensors as subjects performed the above mentioned functional activities. SEW values between the intact limb and the prosthetic limb were computed by integrating vertical ground reaction forces. Intra-class Correlation Coefficients (ICCs) were calculated to determine test-retest reliability and a repeated measure ANOVA was used to establish differences between the prosthetic feet. Results: The ICC values for Test-Retest reliability ranged from 0.84-0.94 for the various functional activities. There was moderate agreement between the SEW values calculated with F-scan and force plates. The SEW values were significantly different between the K3_foot and other feet during level walking and decline walking. During stair ascent, the MP_foot had a significantly higher SEW value than the other feet. There were no differences between feet during incline walking and stair descent. Training resulted in a significant improvement in symmetry from the Baseline session during sit-to-stand, while for stand-to-sit there were no differences between sessions. The PEQ-13 score was not different between sessions, while the Usability scores were significantly different between the K3_foot/MP_foot and K1_foot/K2_foot. The AMP score had a significant increase following Training while the 6MWT score showed a significant increase in the distance walked with the K1_foot, K3_foot and MP_foot over Baseline. The output of SAM did not show any difference in the number of steps or activity level of subjects. There was good to excellent correlation between the SEW values for level walking and other clinical outcome measures. Discussion and Conclusion: The SEW measure had excellent test-retest reliability and the agreement between the F-scan and force plates values could not be established because of a small sample size. The variations in SEW values were the result of distinctive designs of prosthetic feet. The high SEW value of the K3_foot can be attributed to its heel-toe foot plate and "J" shaped ankle spring design, which allowed for greater late stance stability. The active dorsiflexion feature of the MP_foot caused a change in strategy, typically used during stair ascent, resulting in a greater inter-limb symmetry. The SEW measure is a viable method to detect kinetic gait differences among prosthetic feet and represents a resource-effective alternative to traditional gait laboratories. It has several advantages and with further development of in-sole sensor technology, the potential for clinical use due to its relatively low cost instrumentation and minimal subject intervention.</p
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