A feasibility study on the use of low-dimensional simulations for database generation in adaptive chemistry approaches

LES/PDF approaches can be used for simulating challenging turbulent combustion configurations with strong turbulence chemistry interactions. Transported PDF methods are computationally expensive compared to flamelet-like turbulent combustion models. The pre-partitioned adaptive chemistry (PPAC) methodology was developed to address this cost differential. PPAC entails an offline preprocessing stage, where a set of reduced models are generated starting from an initial database of representative compositions. At runtime, this set of reduced models are dynamically utilized during the reaction fractional step leading to computational savings. We have recently combined PPAC with in-situ adaptive tabulation (ISAT) to further reduce the computational cost. We have shown that the combined method reduced the average wall-clock time per time step of large-scale LES/particle PDF simulations of turbulent combustion by 39\%. A key assumption in PPAC is that the initial database used in the offline stage is representative of the compositions encountered at runtime. In our previous study this assumption was trivially satisfied as the initial database consisted of compositions extracted from the turbulent combustion simulation itself. Consequently, a key open question remains as to whether such databases can be generated without having access to the turbulent combustion simulation. Towards answering this question, in the current work, we explore whether the compositions for forming such a database can be extracted from computationally-efficient low-dimensional simulations such as 1D counterflow flames and partially stirred reactors. We show that a database generated using compositions extracted from a partially stirred reactor configuration leads to performance comparable to the optimal case, wherein the database is comprised of compositions extracted directly from the LES/PDF simulation itself

Nationwide surveillance for Telmisartan alone or with combination at real world therapy in Indian patients with hypertension (START)

Background: Angiotensin receptor blockers (ARBs) are amongst the most preferred class of antihypertensive as reported at various evidences or guidelines. However, choice amongst ARBs differs between practicing physicians in real-life scenario. This survey aimed to understand the usage preferences of telmisartan therapy alone and in combination for treating hypertension (HT) among practitioners at various clinical settings in real-life scenario in India.Methods: A cross‑sectional survey was conducted with a pre-validated survey questionnaire consisting of 15 questions pertaining to the telmisartan and its combination usage in HT management. Total 498 registered medical practitioners (mostly physicians and cardiologists) had participated in survey. They were approached for seeking their perception, opinions, and prescribing behaviour. Categorical data was summarized by number (n) and percentage (%) in each category. Data were summarised in frequency tables.Results: Key findings from the data analysed were as follows: Around 20-40% of patients been reported to have co-morbid hypertension and diabetes as reported by majority of the physicians. Preferred class of drug in patients with hypertension with diabetes reported to be ARB. Around 90.36% of doctors reported that telmisartan was the most preferred ARB in patients with hypertension associated with high cardiovascular risk. Around 90.76% of doctors reported for their preference for telmisartan in patients with hypertension for 24-hr BP control. Around 82.93% of doctors preferred telmisartan in patients with hypertension and stroke/post-MI status.Conclusions: Indian healthcare practitioners prefer telmisartan as the most preferred ARB either alone or in a combination in patients with hypertension, including those with comorbidities

Quantitative computational infrared imaging of buoyant diffusion flames

Studies of infrared radiation from turbulent buoyant diffusion flames impinging on structural elements have applications to the development of fire models. A numerical and experimental study of radiation from buoyant diffusion flames with and without impingement on a flat plate is reported. Quantitative images of the radiation intensity from the flames are acquired using a high speed infrared camera. Large eddy simulations are performed using fire dynamics simulator (FDS version 6). The species concentrations and temperature from the simulations are used in conjunction with a narrow-band radiation model (RADCAL) to solve the radiative transfer equation. The computed infrared radiation intensities rendered in the form of images and compared with the measurements. The measured and computed radiation intensities reveal necking and bulging with a characteristic frequency of 7.1 Hz which is in agreement with previous empirical correlations. The results demonstrate the effects of stagnation point boundary layer on the upstream buoyant shear layer. The coupling between these two shear layers presents a model problem for sub-grid scale modeling necessary for future large eddy simulations

Ivabradine: Evidence and current role in cardiovascular diseases and other emerging indications

Increased heart rate (HR) is associated with deleterious effects on several disease conditions. Chronic heart failure (CHF) is one of the cardiovascular diseases with recurrent hospitalization burden and an ongoing drain on health-care expenditure. Despite advancement in medicine, management of CHF remains a challenge to health-care providers. Ivabradine selectively and specifically inhibits the pacemaker I(f) ionic current which reduces the cardiac pacemaker activity. The main effect of ivabradine therapy is the substantial lowering of HR. It does not influence intracardiac conduction, contractility, or ventricular repolarization. As shown in numerous clinical studies, ivabradine improves clinical outcomes and quality of life and reduces the risk of death from heart failure (HF) or other cardiovascular causes. Recently updated HF guidelines recommend ivabradine as a class II indication for reduction of HF hospitalizations. Based on the principle of benefits of reduced HR, the ivabradine in patients with ischemic heart disease, sepsis, and multiple organ dysfunction syndrome has also been studied. It can also be a useful agent for HR reduction in patients with contraindications to use beta-blockers or those who cannot tolerate them. In this review, we provide an overview of efficacy and safety of ivabradine and its combination with currently recommended pharmacological therapy in different conditions. Keywords: Heart failure, Ivabradine, I(f) current, H

Towards computationally-efficient and accurate particle PDF simulations of turbulent combustion using pre-partitioned adaptive chemistry

190 pagesThere is a time critical need for design of fossil fuel based energy conversion devices that attain the dual and usually competing objectives of high efficiency and low pollutant emissions. The design of such devices can be informed by, and in certain instances derived from predictive computations. A crucial component of reacting flow simulations that are predictive is the turbulent combustion model. Probability density function (PDF) methods have been shown to accurately capture flames with strong turbulence chemistry interactions. However, PDF methods are known to be more computationally intensive than simpler topology based approaches such as steady laminar flamelet models. The recently proposed pre-partitioned adaptive chemistry (PPAC) methodology mitigates the cost of using particle PDF methods while maintaining their accuracy. PPAC generates a set of reduced models in an offline preprocessing stage, which are then dynamically utilized at runtime for integrating particle compositions. In the first part of this work, PPAC is augmented by combining it with complementary dimension reduction (rate-controlled constrained equilibrium (RCCE)) and storage retrieval methods (in-situ adaptive tabulation (ISAT)). The combined PPAC-RCCE-ISAT method is shown to outperform standalone PPAC by avoiding redundant direct integrations leading to a significant reduction in the CPU cost, and achieving a sizable reduction in the memory requirement by retaining fewer variables at runtime. Though PPAC has been developed for reducing the computational cost of particle PDF computations, it had previously been tested only in a partially stirred reactor (PaSR). Consequently, an integrated PPAC (-ISAT) particle PDF solver is developed as part of the current work. A detailed assessment of PPAC and PPAC-ISAT in LES/PDF simulations of turbulent combustion is completed using the developed solver. For a large-scale simulation of Sandia flame D, the coupled PPAC-ISAT particle PDF solver is shown to reduce the average wall clock time of a standalone ISAT implementation using the detailed mechanism by 39%, with a minimal loss of accuracy. A key assumption made in the PPAC framework is that the compositions used in the offline preprocessing stage are representative of those encountered at runtime. Hence, the efficient generation of a representative database is crucial to the success of PPAC. The suitability of existing canonical 0D-1D reactors is examined for this purpose. Specifically, compositions obtained from these canonical reactors are compared to the compositions extracted from a variety of direct numerical simulations using an ISAT based approach. We show that the compositions obtained from 1D counterflow flames and PaSR are representative of a significant fraction of the compositions encountered in turbulent combustion simulations. To directly quantify the impact of using databases generated from canonical 0D-1D reactors, we use the coupled PPAC-ISAT particle PDF solver for performing LES/PDF simulations of Sandia flame D. We explore two databases: a first one generated using compositions extracted from 1D counterflow flames, and a second one using compositions from a PaSR. We show that the use of these efficiently generated databases leads to results that are comparable to the case where the database is comprised of compositions extracted from the LES/PDF simulation itself. Finally, avenues for further research that can significantly improve the utility of PPAC for enabling computationally-efficient and accurate particle PDF computations are identified

Formation of Boric Acid by Surface Oxidation of Amorphous Boron Powder: Characterization and Quantitative Estimation

Amorphous Boron Powder (ABP) is used as a fuel in air breathing propulsion systems due to its high gravimetric and volumetric heat value. ABP is sensitive to air and undergoes slow oxidation during storage and handling, leading to the formation of a boric acid layer on the particle surface. This paper describes an analytical method for the estimation of boric acid in ABP. In-house samples obtained from the pilot plant of this laboratory, as well as commercial samples, were assayed for their boric acid content. The study is substantiated by characterization of the ABP samples by SEM with EDX and FTIR. The ageing characteristics of in-house boron powder was also studied

Preparation and characterization of ultrafine RDX

This paper describes the synthesis of ultrafine Hexogen (UF-RDX) of size <5μm by drowning-out crystallization. RDX was precipitated from acetone or dimethylformamide (DMF) solution by reducing the solvent power using either a miscible, non-aqueous antisolvent, n-hexane, or an aqueous antisolvent, water containing polyethylene glycol (PEG). Process parameters such as solvent/ antisolvent ratio, agitation, ultrasonication etc. were studied. UF-RDX was characterized for Brunauer-Emmett-Teller (BET) surface area, X-ray diffraction (XRD), Scanning Electron Microscope (SEM), Fourier Transform Infrared Spectroscopy (FT-IR), Differential Scanning Calorimetry (DSC) and sensitivity tests. In the case of the non-aqueous antisolvent, the precipitated RDX crystals were rod shaped of diameter <1 μm. For the aqueous antisolvent, oval shaped crystals (<5 μm) were precipitated. UF-RDX was found to be more sensitive to impact and less friction sensitive compared to production grade RDX (60-80 μm)

Preparation of Nano Aluminium Powder (NAP) using a Thermal Plasma: Process Development and Characterization

A bottom up approach for the preparation of Nano Aluminium Powder (NAP) using a Transferred Arc Thermal Plasma Reactor (TAPR) is described. The aluminium block is subjected to evaporation by the application of a thermal plasma. The aluminium vapour produced is rapidly quenched to room temperature resulting in crystallization of the aluminium vapour in nano-particulate form. Various process parameters, such as the plasma torch power, reactor pressure and plasma gas composition were optimized. This paper also describes the characterization of NAP by analytical methods, for the estimation of the Active Aluminium Content (AAC), Total Aluminium Content (TAC), XRD, bulk density, BET surface area, HR-TEM etc. The results are compared with those for samples prepared in other thermal plasma reactors, such as the DC Arc Plasma Reactor (DCAPR) and the RF Induction Thermal Plasma Reactor (RFITPR), and for commercially available NAP samples (ALEX, prepared by the EEW technique)