PTAS for Minimax Approval Voting

We consider Approval Voting systems where each voter decides on a subset to candidates he/she approves. We focus on the optimization problem of finding the committee of fixed size k minimizing the maximal Hamming distance from a vote. In this paper we give a PTAS for this problem and hence resolve the open question raised by Carragianis et al. [AAAI'10]. The result is obtained by adapting the techniques developed by Li et al. [JACM'02] originally used for the less constrained Closest String problem. The technique relies on extracting information and structural properties of constant size subsets of votes.Comment: 15 pages, 1 figur

Equivariant Giambelli and determinantal restriction formulas for the Grassmannian

The main result of the paper is a determinantal formula for the restriction to a torus fixed point of the equivariant class of a Schubert subvariety in the torus equivariant integral cohomology ring of the Grassmannian. As a corollary, we obtain an equivariant version of the Giambelli formula.Comment: 16 pages, 3 figures, LaTex, uses epsfig and psfrag; for the revised version: title changed; Proof of Theorem 3 changed; 3 references added and 1 deleted; other minor change

Packet flow analysis in IP networks via abstract interpretation

Static analysis (aka offline analysis) of a model of an IP network is useful for understanding, debugging, and verifying packet flow properties of the network. There have been static analysis approaches proposed in the literature for networks based on model checking as well as graph reachability. Abstract interpretation is a method that has typically been applied to static analysis of programs. We propose a new, abstract-interpretation based approach for analysis of networks. We formalize our approach, mention its correctness guarantee, and demonstrate its flexibility in addressing multiple network-analysis problems that have been previously solved via tailor-made approaches. Finally, we investigate an application of our analysis to a novel problem -- inferring a high-level policy for the network -- which has been addressed in the past only in the restricted single-router setting.Comment: 8 page

Utility of Surgical APGAR Score in Predicting Postoperative Morbidity and Mortality in patients Undergoing Laparotomy: A Prospective study

BACKGROUND: Health facilities strive to offer quality surgical care by minimizing postoperative complications. Predicting complications facilitates objective clinical decision making during recovery. Compared to existing morbidity and mortality predictive scores, the Surgical Apgar Score is simple and effective. Morbidity and mortality in patients undergoing laparotomy are high; an effective scoring system can reduce these. OBJECTIVE: To determine the utility of the Surgical Apgar Score in predicting the thirty day major postoperative complications rates for patients undergoing laporotomy. Study Design: Prospective descriptive study. Study Population: 154 patients aged 13 years and above undergoing laparotomy at Madras Medical College & Rajiv Gandhi Govt. General Hospital, Chennai were selected by consecutive sampling until the desired sample size was achieved. Study Duration: March 2016 to September 2016. MATERIAL AND METHODS: Intra operative values of the lowest mean arterial pressure, the lowest heart rate and the blood loss were collected using a questionnaire immediately after surgery and the Surgical Apgar Score was derived for each patient. The occurrence of major complications and the mortality rate was determined during a thirty day period starting immediately after surgery. Data was obtained from the admitting ward, the ICU and surgical outpatient clinic notes. Major complication definitions were according to the one described by Copeland et al. Data collected was entered and analyzed using statistics. P values were generated using t test for means, x2 for comparison of proportions, analysis of variance (ANOVA) and where applicable Fischer’s exact test. Results were presented in graph, tables and charts. RESULTS: 154 patients were recruited of which 2 were lost on follow up. The mean age in this study was 35.18 years. This study had a skewed distribution of gender with 75% of patients being male. The most common reason for laparotomy is penetrating abdominal injury. This is18.4% of the overall cause of laparotomy. It could be seen that emergency laparotomy is the major cause for the development of major postoperative complications when compared to elective laparotomies. Female sex, 40 years or lesser age and surgery time more than 2 hours are other noted factors in our study that was found to be associated with a significantly higher rates of complications. It can be observed in our study that, long duration of surgery and a low mean Surgical Apgar Score is having a strong association. From our study we can interpret that, patients having a SAS 0f 0 – 4 who belong to the high risk group had a higher complication rate of 58.3% when compared with the patients having a score of 8 – 10 who belong to low risk group. This group had a lower complication rate of 16.6%. It was statistically significant too. This clearly demonstrates the efficacy of the Surgical Apgar Score in selecting patients who are at a higher risk of developing major complications from patients who are at an average risk of developing complications. CONCLUSION: Laparotomy surgery is associated with significant morbidity and mortality. The SAS, despite using simple and widely available intra-operative parameters, is useful tool to predict occurrence of 30 day major complications and mortality following laporotomy surgery

High precision laser radar tracking device

This thesis explores a relatively new Solid Silver Thin Film Source technology, for the implementation of a novel High Precision Laser Radar Tracking device. The process which consists of a Ag+-Na+ ion exchange, is designed in two steps. It utilizes an initial electric field-aided ion exchange step for a predeposition, and a subsequent second diffusion step to force the profile latitude necessary for optimization of the device. While the entire project of implementing this device, consists of analyzing, processing, polishing and testing, this thesis covers only the process aspect in detail. The success achieved by obtaining the required Power Coupling Ratio curve on a Simple Coupler, demonstrates a novel integrated optic multimode feed for a Monopulse LIDAR application

Quantum versus Semiclassical Description of Selftrapping: Anharmonic Effects

Selftrapping has been traditionally studied on the assumption that quasiparticles interact with harmonic phonons and that this interaction is linear in the displacement of the phonon. To complement recent semiclassical studies of anharmonicity and nonlinearity in this context, we present below a fully quantum mechanical analysis of a two-site system, where the oscillator is described by a tunably anharmonic potential, with a square well with infinite walls and the harmonic potential as its extreme limits, and wherein the interaction is nonlinear in the oscillator displacement. We find that even highly anharmonic polarons behave similar to their harmonic counterparts in that selftrapping is preserved for long times in the limit of strong coupling, and that the polaronic tunneling time scale depends exponentially on the polaron binding energy. Further, in agreement, with earlier results related to harmonic polarons, the semiclassical approximation agrees with the full quantum result in the massive oscillator limit of small oscillator frequency and strong quasiparticle-oscillator coupling.Comment: 10 pages, 6 figures, to appear in Phys. Rev.