A time-frequency analysis method for radar scattering

A time-frequency analysis method to study electromagnetic scattering is presented and demonstrated using canonical objects. The time-frequency analysis method utilizes the Bargmann transform to formulate the signal representation in phase space. The use of the Bargmann transform leads to an attractive parametric signal representation in terms of complex polynomials, and elliptical filters can be constructed to crop or extract selected areas of the phase plane. The signal representation and filtering operations are demonstrated using scattering responses from spheres and thin wires, and the prominent scattering features are identified and extracted     

Heat capacities of polyethylene and linear fluoropolymers

Heat capacities at constant pressure, C_p, and at constant volume C_v, were calculated with the help of normal mode frequency spectra and compared to experimental data for crystalline or semicrystalline polyethylene, poly(vinyl fluoride), poly(vinylidene fluoride), polytrifluooroethylene and poly(tetrafluoroethylene). A calculation scheme using a Tarasov function for 2N skeletal vibrational modes and an approximation of the residual 7N normal modes from known data on polyethylene and polytetrafluoroethylene is developed for all homologous, linear fluoropolymers. N is the number of carbon backbone atoms of the repeating unit. Calculations can be carried out over the whole temperature range 0 K to melting. For the two theta temperatures and the constant A₀ used for C_v to C_p conversion, fluorine-concentration dependent curves are given. The relations are expected to hold also for copolymers and blends of intermediate fluorine contents. Recommended experimental (data bank) heat capacities agree to ±2.5% with the calculations.     

On challenges of model transformation from UML to Alloy

The Unified Modeling Language (UML) is the de facto language used in the industry for software specifications. Once an application has been specified, Model Driven Architecture (MDA) techniques can be applied to generate code from such specifications. Since implementing a system based on a faulty design requires additional cost and effort, it is important to analyse the UML models at earlier stages of the software development lifecycle. This paper focuses on utilizing MDA techniques to deal with the analysis of UML models and identify design faults within a specification. Specifically, we show how UML models can be automatically transformed into Alloy which, in turn, can be automatically analysed by the Alloy Analyzer. The proposed approach relies on MDA techniques to transform UML models to Alloy. This paper reports on the challenges of the model transformation from UML class diagrams and OCL to Alloy. Those issues are caused by fundamental differences in the design philosophy of UML and Alloy. To facilitate better the representation of Alloy concepts in the UML, the paper draws on the lessons learnt and presents a UML profile for Alloy.     

Event‐triggered optimal tracking control of nonlinear systems

We propose a novel event‐triggered optimal tracking control algorithm for nonlinear systems with an infinite horizon discounted cost. The problem is formulated by appropriately augmenting the system and the reference dynamics and then using ideas from reinforcement learning to provide a solution. Namely, a critic network is used to estimate the optimal cost while an actor network is used to approximate the optimal event‐triggered controller. Because the actor network updates only when an event occurs, we shall use a zero‐order hold along with appropriate tuning laws to encounter for this behavior. Because we have dynamics that evolve in continuous and discrete time, we write the closed‐loop system as an impulsive model and prove asymptotic stability of the equilibrium point and Zeno behavior exclusion. Simulation results of a helicopter, a one‐link rigid robot under gravitation field, and a controlled Van‐der‐Pol oscillator are presented to show the efficacy of the proposed approach. Copyright © 2016 John Wiley & Sons, Ltd.     

Physical Characterization of Anhydrous and Hydrous Forms of the Hydrochloride Salt of BVT.5182 A Novel 5-HT6 Receptor Antagonist

ABSTRACT

The physicochemical properties of 1-benzenesulfonyl-4-(piperazin-1-yl)-indole hydrochloride, a novel 5-HT₆ receptor antagonist for the treatment of obesity were characterized. Two solid state forms were identified at ambient conditions (23°C): an anhydrate form (1) and a hydrate form (2), with 1.5 moles of H₂O. The latter easily dehydrates and rehydrates without affecting the crystal morphology. Investigations of the propensity for interconversion between the two forms reveal that a) conversion of 2→1 takes place above 145°C and that b) conversion of 1→2 only occurs after crystallization from supersaturated aqueous solutions at a water activity ≥0.94 or in the presence of comparable amounts of crystals of 2 in water at ambient conditions. However, in an equimolar suspension of 1 and 2 at 37°C no phase transformation was observed. Thus, the difference in chemical potential between the two forms is small. Form 1 was shown to have overall favorable solid state properties and, hence, considered the preferred form for continued pharmaceutical development. The characterization was performed by means of light microscopy, scanning electron microscopy, powder X-ray diffraction, FTIR/NIR-spectroscopy, differential scanning calorimetry, hot stage microscopy, thermogravimetry, dynamic vapor sorption, Karl Fischer water content determination, phase stability studies of suspensions, solubility, and intrinsic dissolution rate measurements.     

The influence of spiral jet-milling on the physicochemical properties of carbamazepine form III crystals: Quality by design approach

The purpose of this study was to investigate the influence of spiral jet-milling process on the physicochemical characteristics of α polymorphic active pharmaceutical ingredient, using Carbamazepine form III as a model drug, and taking into consideration Quality by Design (QbD) approach to pharmaceutical development. A 2^(4-1) factorial screening design was implemented to identify the spiral jet-milling process variables that significantly affect the particle size distribution of milled samples. Diameter of injector nozzles, diameter of ring nozzles and air pressure were selected for further analysis using a 2^(3-1) factorial experimental design. Particle size distribution of additional samples was determined, while physicochemical properties were examined by differential scanning calorimetry (DSC), hot-stage polarized microscopy (HSPM), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and compared to those of un-milled drug. The gathered results shown that applied experimental design approach is capable to predict material behavior and could help in better understanding of material behavior during jet-milling process. Created design space (DS) provides assurance of product quality, expressed as the powder particle sizes lower than 5 μm, as well as, in initial polymorph form existence after jet-milling through combination and interaction of input variables.     

Laparoscopic splenectomy in beta-thalassemia major patients. Advantages and disadvantages

BACKGROUND: Splenectomy is indicated in patients with thalassemia major when they develop hypersplenism with subsequent need for increased transfusions. Extreme splenomegaly is considered a restrictive factor for laparoscopic splenectomy in these patients. METHODS: Laparoscopic splenectomy was undertaken in 12 beta-thalassemia major patients with massive splenomegaly. The devascularization of the organ was performed with serial ligations of the splenic vessels starting from the lower pole of the organ. The spleen was extracted from the abdominal cavity through a 5-cm incision in the left iliac fossa, which incorporated two port sites. RESULTS: The procedure was concluded laparoscopically in 10 cases, while two patients were converted due to difficulty in controlling bleeding from branches of the splenic vein. The patients tolerated the procedure well and had a postoperative hospital stay of 3-6 days. CONCLUSIONS: From our limited initial experience it seems that laparoscopic splenectomy in the difficult setting of thalassemia major patients is feasible, but extreme care is required in order to avoid hemorrhagic complications.     

Failure Analysis of a Cast Mn-Bronze Propeller

The investigation of a failure of a cast manganese bronze propeller, fractured after a short service period (~4–5 months), was conducted. Chemical analysis, visual inspection, optical microscopy, fractographic evaluation, SEM/EDS analysis, and hardness testing were used as the principal analytical tools for the failure investigation. The findings suggest that the failure occurred due to fatigue mechanism under low stress conditions. The non-conformities detected in material chemical composition, as well as the presence of internal and surface flaws could be considered as the main contributors of the premature failure of the propeller.     

Data-enabled extremum seeking: A cooperative concurrent learning-based approach

This paper introduces a new class of feedback-based data-driven extremum seeking algorithms for the solution of model-free optimization problems in smooth continuous-time dynamical systems. The novelty of the algorithms lies on the incorporation of memory to store recorded data that enables the use of information-rich datasets during the optimization process, and allows to dispense with the time-varying dither excitation signal needed by standard extremum seeking algorithms that rely on a persistence of excitation (PE) condition. The model-free optimization dynamics are developed for single-agent systems, as well as for multi-agent systems with communication graphs that allow agents to share their state information while preserving the privacy of their individual data. In both cases, sufficient richness conditions on the recorded data, as well as suitable optimization dynamics modeled by ordinary differential equations are characterized in order to guarantee convergence to a neighborhood of the solution of the extremum seeking problems. The performance of the algorithms is illustrated via different numerical examples in the context of source-seeking problems in multivehicle systems.