Bearing-Based Distributed Control and Estimation of Multi-Agent Systems

This paper studies the distributed control and estimation of multi-agent systems based on bearing information. In particular, we consider two problems: (i) the distributed control of bearing-constrained formations using relative position measurements and (ii) the distributed localization of sensor networks using bearing measurements. Both of the two problems are considered in arbitrary dimensional spaces. The analyses of the two problems rely on the recently developed bearing rigidity theory. We show that the two problems have the same mathematical formulation and can be solved by identical protocols. The proposed controller and estimator can globally solve the two problems without ambiguity. The results are supported with illustrative simulations.Comment: 6 pages, to appear in the 2015 European Control Conferenc

Bearing-Based Formation Maneuvering

This paper studies the problem of multi-agent formation maneuver control where both of the centroid and scale of a formation are required to track given velocity references while maintaining the formation shape. Unlike the conventional approaches where the target formation is defined by inter-neighbor relative positions or distances, we propose a bearing-based approach where the target formation is defined by inter-neighbor bearings. Due to the invariance of the bearings, the bearing-based approach provides a natural solution to formation scale control. We assume the dynamics of each agent as a single integrator and propose a globally stable proportional-integral formation maneuver control law. It is shown that at least two leaders are required to collaborate in order to control the centroid and scale of the formation whereas the followers are not required to have access to any global information, such as the velocities of the leaders.Comment: To appear in the 2015 IEEE Multi-Conference on Systems and Control (MSC2015); this is the final versio

Entropy balancing is doubly robust

Covariate balance is a conventional key diagnostic for methods used estimating causal effects from observational studies. Recently, there is an emerging interest in directly incorporating covariate balance in the estimation. We study a recently proposed entropy maximization method called Entropy Balancing (EB), which exactly matches the covariate moments for the different experimental groups in its optimization problem. We show EB is doubly robust with respect to linear outcome regression and logistic propensity score regression, and it reaches the asymptotic semiparametric variance bound when both regressions are correctly specified. This is surprising to us because there is no attempt to model the outcome or the treatment assignment in the original proposal of EB. Our theoretical results and simulations suggest that EB is a very appealing alternative to the conventional weighting estimators that estimate the propensity score by maximum likelihood.Comment: 23 pages, 6 figures, Journal of Causal Inference 201

A survey of Top 200 Drugs—Inconsistent Practice of Drug Strength Expression for Drugs Containing Salt Forms

Many ionizable drugs are developed and marketed as salt forms. However, there are no clear US regulatory guidelines on drug strength labeling for salts. The strengths of some drugs are expressed as salts and some as free acids/bases. This study surveyed the top 200 US drugs to assess the common practice in industry. The top 200 drugs prescribed in the United States were included in this survey. The drugs containing active pharmaceutical ingredient (API) salts were selected for analysis. Generic or combination products with redundant API salts were excluded. The package insert of each selected drug was reviewed, and the information on drug strength expression was extracted and categorized. Out of the top 200 drugs, 59 unique API salts were identified. The drug strengths were expressed as salts for 32 drugs (54%) and as free acids/bases for 27 drugs (46%). The survey results revealed the inconsistent practice among the industries regarding the drug strength expression for salts. Non-harmonized labeling practice can lead to confusions, potential calculation/dosing errors, and complications in labeling new products. The authors recommend the US Food and Drug Administration to standardize the labeling format for salts and preferably express the drug strengths based on the free acid/base forms. © 2011 Wiley Periodicals, Inc. and the American Pharmacists Association

Higher Derivative Corrections to O-plane Actions: NS-NS Sector

We classify all possible two- and four-derivative couplings of bulk NS-NS sector fields to a single Op-plane which are compatible with diffeomorphism invariance and B-field gauge invariance. This is applicable to type IIA or IIB superstrings or to the bosonic string. We then consider this general action in various classes of backgrounds that admit a U(1) isometry and determine the constraints on the couplings from consistency with T-duality. We show that this consistency requires the two-derivative action to vanish, and the entire non-linear four-derivative action is fixed up to one overall constant which can be determined by comparison with a two-point scattering amplitude. The resulting action is consistent with all previously computed couplings.Comment: 54 page

Stability of levetiracetam oral solution repackaged in oral plastic syringes

Purpose The long-term stability of levetiracetam solution in oral syringes was investigated in order to define a suitable beyond-use date and demonstrate the feasibility of storing prepared syringes for extended periods as an alternative to commercial levetiracetam unit dose cups. Methods Levetiracetam oral solution (100 mg/mL) was drawn into 1- and 10-mL amber polypropylene oral syringes. Triplicate samples of the syringe preparations were stored at refrigeration (2–8 °C) or room temperature (20–25 °C) and evaluated at monthly intervals for up to six months. At each time point, the samples were visually inspected and levetiracetam stability was assessed via pH measurement and high-performance liquid chromatography (HPLC). A short-term forced degradation study was conducted to confirm that the HPLC assay method was stability indicating. Results Over the six-month storage period, there was no significant change in either the visual appearance or pH of any of the levetiracetam samples. The results of serial HPLC assessment indicated that at least 97% of the initial levetiracetam concentration was retained in all samples of 1- and 10-mL oral syringes at both refrigeration and room temperature. Although this study was conducted using a generic product, the stability data obtained may be applied in repackaging decisions regarding other generic formulations of levetiracetam with similar excipient compositions. Conclusion Commercial levetiracetam 100-mg/mL oral solution was stable for up to six months in amber polypropylene oral syringes stored at both refrigeration and room temperature conditions