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1.
We introduce a treatment of parametric estimation in which optimality of an estimator is measured in probability rather than in variance (the measure for which the strongest general results are known in statistics). Our motivation is
that the quality of an approximation algorithm is measured by the probability that it fails to approximate the desired quantity
within a set tolerance. We concentrate on the Gaussian distribution and show that the sample mean is the unique “best” estimator,
in probability, for the mean of a Gaussian distribution. We also extend this method to general penalty functions and to multidimensional
spherically symmetric Gaussians.
The algorithmic significance of studying the Gaussian distribution is established by showing that determining the average
matching size in a graph is #P-hard, and moreover approximating it reduces to estimating the mean of a random variable that (under some mild conditions)
has a distribution closely approximating a Gaussian. This random variable is (essentially) polynomial time samplable, thereby
yielding an FPRAS for the problem. 相似文献
2.
In this study, combustion of methane was simulated using four kinetic models of methane in CHEMKIN 4.1.1 for 0-D closed internal combustion (IC) engine reactor. Two detailed (GRIMECH3.0 & UBC MECH2.0) and two reduced (One step & Four steps) models were examined for various IC engine designs. The detailed models (GRIMECH3.0, & UBC MECH2.0) and 4-step models successfully predicted the combustion while global model was unable to predict any combustion reaction. This study illustrated that the detailed model sh... 相似文献
3.
The permutation representation afforded by a Coxeter group W acting on the cosets of a standard parabolic subgroup inherits many nice properties from W such as a shellable Bruhat order and a flat deformation over ?[q] to a representation of the corresponding Hecke algebra. In this paper we define a larger class of “quasiparabolic” subgroups (more generally, quasiparabolic W-sets), and show that they also inherit these properties. Our motivating example is the action of the symmetric group on fixed-point-free involutions by conjugation. 相似文献
4.
Consider the polyhedron represented by the dual of the LP formulation of the maximums–t flow problem. It is well known that the vertices of this polyhedron are integral, and can be viewed ass–t cuts in the given graph. In this paper we show that not alls–t cuts appear as vertices, and we give a characterization. We also characterize pairs of cuts that form edges of this polyhedron. Finally, we show a set of inequalities such that the corresponding polyhedron has as its vertices alls–t cuts.Work done at the Department of Computer Science and Engineering, Indian Institute of Technology, Delhi, India. 相似文献
5.
Photoinduced electron transfer between triplet erythrosin dianion and highly charged ionic quenchers
Asim Mansha Günter Grampp Stephan Landgraf 《Monatshefte für Chemie / Chemical Monthly》2011,55(25):11-17
Abstract
The lifetime of the lowest triplet state of the dianion erythrosin B depends on its concentration because of self-quenching. The self-quenching rate constants vary with the solution viscosity at room temperature. Dextrose was used to change the viscosity of aqueous solutions in the range 1 ≤ η ≤ 5.31 cP. Photoinduced electron transfer reactions between the triplet state of the erythrosin dianion and the highly charged ionic quenchers K4[Fe(CN)6] and K4[Mo(CN)8] were investigated in aqueous borate buffer solutions at pH 9.2 using flash photolysis. Electron transfer rates vary from 3.0 × 108 to 1.4 × 108 M−1 s−1 depending on viscosity. 相似文献6.
Deeparnab Chakrabarty Nikhil R. Devanur Vijay V. Vazirani 《Mathematical Programming》2011,130(1):1-32
Determining the integrality gap of the bidirected cut relaxation for the metric Steiner tree problem, and exploiting it algorithmically, is a long-standing open problem. We use geometry to define an LP whose dual is equivalent to this relaxation. This opens up the possibility of using the primal-dual schema in a geometric setting for designing an algorithm for this problem. Using this approach, we obtain a 4/3 factor algorithm and integrality gap bound for the case of quasi-bipartite graphs; the previous best integrality gap upper bound being 3/2 (Rajagopalan and Vazirani in On the bidirected cut relaxation for the metric Steiner tree problem, 1999). We also obtain a factor \({\sqrt{2}}\) strongly polynomial algorithm for this class of graphs. A key difficulty experienced by researchers in working with the bidirected cut relaxation was that any reasonable dual growth procedure produces extremely unwieldy dual solutions. A new algorithmic idea helps finesse this difficulty—that of reducing the cost of certain edges and constructing the dual in this altered instance—and this idea can be extracted into a new technique for running the primal-dual schema in the setting of approximation algorithms. 相似文献
7.
Muhammad Zahid Günter Grampp Asim Mansha Ijaz Ahmad Bhatti Sadia Asim 《Journal of fluorescence》2013,23(4):829-837
Four cyano groups have been substituted on the aromatic ring of p-hydroquinone (2,3,5,6-tetracyanohydroquinone) in order to study the enhanced photoacidity of this molecule. The acid-base equilibria have been studied using absorption (for ground state pKa) and fluorescence (excited state pKa) spectra. Three distinct species (neutral, anionic and dianionic forms) were observed in the ground state and only two species (anionic and dianionic forms) were found in the excited state when studied at different pH/Ho in water. Absorption and emission characteristics were studied in various organic solvents, including protic and aprotic solvents. Deprotonation was also investigated using binary mixtures. It has been revealed that absorption and emission spectra are considerably changed with change in media. Proton transfer to the solvent has been observed in various solvents. 相似文献
8.
Athanasiadis introduced separating walls for a region in the extended Shi arrangement and used them to generalize the Narayana numbers. In this paper, we fix a hyperplane in the extended Shi arrangement for type A and calculate the number of dominant regions which have the fixed hyperplane as a separating wall; that is, regions where the hyperplane supports a facet of the region and separates the region from the origin. 相似文献
9.
Aranyak Mehta Scott Shenker Vijay V. Vazirani 《Journal of Algorithms in Cognition, Informatics and Logic》2006,58(2):150-164
We describe an iterative fixed point approach for the following stochastic optimization problem: given a multicast tree and probability distributions of user utilities, find an optimal posted price mechanism—i.e., compute prices to offer the users in order to maximize the expected profit of the service provider. We show that any optimum pricing is a fixed point of an efficiently computable function. We can then apply the non-linear Jacobi and Gauss–Seidel methods of coordinate descent. We provide proof of convergence to the optimum prices for special cases of utility distributions and tree edge costs. 相似文献
10.
Anam Iqbal Syed Ali Raza Naqvi Rashid Rasheed Asim Mansha Matloob Ahmad Ameer Fawad Zahoor 《Applied biochemistry and biotechnology》2018,185(1):127-139
Bacterial infection poses life-threatening challenge to humanity and stimulates to the researchers for developing better diagnostic and therapeutic agents complying with existing theranostic techniques. Nuclear medicine technique helps to visualize hard-to-diagnose deep-seated bacterial infections using radionuclide-labeled tracer agents. Metronidazole is an antiprotozoal antibiotic that serves as a preeminent anaerobic chemotherapeutic agent. The aim of this study was to develop technetium-99m-labeled metronidazole radiotracer for the detection of deep-seated bacterial infections. Radiosynthesis of 99mTc-metronidazole was carried by reacting reduced technetium-99m and metronidazole at neutral pH for 30 min. The stannous chloride dihydrate was used as the reducing agent. At optimum radiolabeling conditions, ~ 94% radiochemical was obtained. Quality control analysis was carried out with a chromatographic paper and instant thin-layer chromatographic analysis. The biodistribution study of radiochemical was performed using Escherichia coli bacterial infection-induced rat model. The scintigraphic study was performed using E. coli bacterial infection-induced rabbit model. The results showed promising accumulation at the site of infection and its rapid clearance from the body. The tracer showed target-to-non-target ratio 5.57 ± 0.04 at 1 h post-injection. The results showed that 99mTc-MNZ has promising potential to accumulate at E. coli bacterial infection that can be used for E. coli infection imaging. 相似文献