34 research outputs found
Promotion of CO Insertion into Metal Alkyl Bonds by Polar Molecules. Rate-Determining Displacement of an Agostic C-H Bond supplementary data
No full textSupplemental data for unpublished PNAS manuscript 201816339
Synthesis of ZnO nanorods and observation of resistive switching memory in ZnO based polymer nanocomposites
No full textDevelopment of cloxacillin loaded multiple-unit alginate-based floating system by emulsion–gelation method
No full textModified starch (cationized)–alginate beads containing aceclofenac: Formulation optimization using central composite design
No full textMonitoring for Reliable and Secure Power Management Integrated Circuits via Built-In Self-Test
Get PDFabstract: Power management circuits are employed in most electronic integrated systems, including applications for automotive, IoT, and smart wearables. Oftentimes, these power management circuits become a single point of system failure, and since they are present in most modern electronic devices, they become a target for hardware security attacks. Digital circuits are typically more prone to security attacks compared to analog circuits, but malfunctions in digital circuitry can affect the analog performance/parameters of power management circuits. This research studies the effect that these hacks will have on the analog performance of power circuits, specifically linear and switching power regulators/converters. Apart from security attacks, these circuits suffer from performance degradations due to temperature, aging, and load stress. Power management circuits usually consist of regulators or converters that regulate the load’s voltage supply by employing a feedback loop, and the stability of the feedback loop is a critical parameter in the system design. Oftentimes, the passive components employed in these circuits shift in value over varying conditions and may cause instability within the power converter. Therefore, variations in the passive components, as well as malicious hardware security attacks, can degrade regulator performance and affect the system’s stability. The traditional ways of detecting phase margin, which indicates system stability, employ techniques that require the converter to be in open loop, and hence can’t be used while the system is deployed in-the-field under normal operation. Aging of components and security attacks may occur after the power management systems have completed post-production test and have been deployed, and they may not cause catastrophic failure of the system, hence making them difficult to detect. These two issues of component variations and security attacks can be detected during normal operation over the product lifetime, if the frequency response of the power converter can be monitored in-situ and in-field. This work presents a method to monitor the phase margin (stability) of a power converter without affecting its normal mode of operation by injecting a white noise/ pseudo random binary sequence (PRBS). Furthermore, this work investigates the analog performance parameters, including phase margin, that are affected by various digital hacks on the control circuitry associated with power converters. A case study of potential hardware attacks is completed for a linear low-dropout regulator (LDO).Dissertation/ThesisMasters Thesis Electrical Engineering 201
Appraisal of Data Assimilation Techniques for Dynamical Downscaling of the Structure and Intensity of Tropical Cyclones
No full textChallenges in fluid flow simulations using Exascale computing
No full textIn this paper, I discuss the challenges in porting hydrodynamic codes to futuristic exascale HPC systems. In particular, we describe the computational complexities of finite difference method, pseudo-spectral method, and Fast Fourier Transform (FFT). We show how global data communication among the processors brings down the efficiency of pseudo-spectral codes and FFT. It is argued that FFT scaling may saturate at 1/2 million processors. However, finite difference and finite volume codes scale well beyond million processors, hence they are likely candidates to be tried on exascale systems. The codes based on spectral-element and Fourier continuation, that are more accurate than finite difference, could also scale well on such systems.The author thanks all the co-developers of FFTK, TARANG, and finite difference code of our group. Some of the key contributors to the codes are Anando Chatterjee, Rosan Samuel, Shaswat Bhattacharya, Ravi Samtaney, Fahad Anwer, Gaurav Gautam, Abhishek Kumar, Mani Chandra, Akash Anand, Awanish Tiwari, and Soumyadeep Chatterjee. In addition, author is grateful to Akash Anand, Samar Aseeri, Rooh Khurram, Bilel Hadri, V. Balaji, and Preeti Malakar for discussion and ideas; and to Ritu Arora, Venkatesh Shenoy, and Amitava Majumdar for organzing wonderful conference “Software Challenges to Exascale Computing (SCEC)”. Funding: This study was funded by research grants INT/RUS/RSF/P-03 by the Department of Science and Technology India. Our numerical simulations were performed on Cray XC40 (Shaheen II) and Blue Gene/P (Shaheen I) at KAUST supercomputing laboratory, Saudi Arabia, through project k105
Catalytic transformations of small molecules by transition metal pincer complexes
No full textThis thesis dissertation has been divided into two parts: (1) Study of nitrogen splitting and reduction to ammonia by pincer ligated molybdenum complexes, and (2) Study of pincer based catalytic systems capable of affecting acceptorless and transfer alkane dehydrogenation, and dehydrogenation with secondary reactions such as olefin coupling.
Part-1
We study the key mechanistic steps of N–N bond cleavage and nitride protonation. The role of halides (Cl⁻, Br⁻, and I⁻) bound to the molybdenum has been investigated in the N–N bond cleavage. An unanticipated sequence of addition of protons and electrons to the molybdenum-nitride core has been discussed for six (PYP)Moᴵⱽ(≡N)X systems (Y = N and S, and X = Cl⁻, Br⁻, and I⁻). We also calculate that the molybdenum trihalide complex is an in-cycle species in the catalytic cycle for reduction of N₂.
We have studied, in great details, the reduction of (PNP)MoᴵᴵᴵX₃ complexes to (PNP)MoᴵX active catalytic species responsible for cleaving N₂. The role of halides (Cl⁻, Br⁻, and I⁻) bound to the molybdenum has been investigated for the reduction of molybdenum(III) cores. Based on mechanistic and structural insights we have proposed improved catalysts that can potentially function with milder sources of reducing agents. Synthetic efforts to experimentally characterize the new catalyst is underway.
We also discuss the development of new molybdenum(III) complexes that can activate and cleave N₂ in the presence of bases. The ligand design, harnesses the acidic protons on the ligand periphery for N₂ cleavage and taps into a Mo(III)/Mo(VI) cycle of N₂ reduction, essentially bypassing the reduction of Mo(III).
Part-2
Di-isopropylphosphino substituted pincer-ligated iridium catalysts are found to be significantly more effective for the dehydrogenation of simple tertiary amines to give enamines than the previously reported di-t-butylphosphino substituted species. It was reported that the di-isopropylphosphino substituted complexes catalyze dehydrogenation of several β-functionalized tertiary amines to give the corresponding 1,2-difunctionalized olefins. The di-t-butylphosphino substituted species are ineffective for such substrates; presumably the marked difference is attributable to the lesser crowding of the di-isopropylphosphino substituted catalysts. Experimentally determined kinetic isotope effects in conjunction with DFT-based analysis support a dehydrogenation mechanism involving initial pre-equilibrium oxidative addition of the amine α C-H bond followed by rate-determining elimination of the β-C-H bond.
Iridium complexes bearing PCP-type pincer-ligands are the most effective catalysts reported to date for the low-temperature (≤ ca. 200 °C) dehydrogenation of alkanes. The (ⁱᴾʳxanPSP)Ru complex has been reported to catalyze alkane transfer dehydrogenation of the benchmark cyclooctane/t-butylethylene (COA/TBE) couple with turnover frequencies up to ca. 1 s⁻¹ at 150 °C and 0.2 s⁻¹ at 120 °C, the highest rates for alkane dehydrogenation ever reported at such temperatures. Dehydrogenation of n-octane, however, was repored to be much less effective. DFT calculations allow us to explain why (ⁱᴾʳxanPSP)Ru is more effective than (ⁱᴾʳPCP)Ir for dehydrogenation of COA while the reverse is true for dehydrogenation of n-alkanes. Considering only in-cycle species and simple olefin complexes, the (ⁱᴾʳxanPSP)Ru fragment is calculated to be much more active than (ⁱᴾʳPCP)Ir for dehydrogenation of both COA and n-alkanes. However, the resting state in the (ⁱᴾʳxanPSP)Ru-catalyzed transfer dehydrogenation of n-alkane is a very stable linear-allyl hydride complex, whereas the corresponding cyclooctenyl hydride is much less stable.
We also report the synthesis and characterization of (ᵗᴮᵘ⁴PPClP)RuHCl and (ᵗᴮᵘ⁴PPᴴP)RuH₄ complexes. The formation of this species is from a rather unusual metalation reaction of ᵗᴮᵘ⁴PPᴴ ligand and [(p-cymene)RuCl₂]₂ Ru(II) precursor. The thermodynamic favorability of initially formed (ᵗᴮᵘ⁴PPᴴP)RuCl₂ undergoing a net hydride chloride exchange, to form the new complex, highlights the potential of an unusual metal-ligand cooperativity that this ligand was designed for. A priori, the thermodynamic drive for this unusual reactivity comes from the stability of a Ru(II) hydride chloride fragment rather than the formation of an otherwise strong Ru–H bond. Work is currently underway to synthesize the (ᵗᴮᵘ⁴PPᴴP)Ru(C₂H₄) complex as catalyst that will be explored for transfer dehydrogenation of alkanes with sacrificial olefins, including the metal-ligand cooperativity that has been identified in this work.
We report an iridium acetate complex with a fluorinated Phebox ligand (2,6-bis(4,4-dimethyl-4,5-dihydrooxazol-2-yl)-3,5-bis(trifluoromethyl)phenyl) that is a highly effective catalyst for acceptorless dehydrogenation of alkanes. Under typical acceptorless dehydrogenation conditions a high turnover frequency is obtained, which is limited by the rate of expulsion of H₂ from the reaction solution. Rates and turnover numbers for acceptorless dehydrogenation are significantly greater than found for the non-fluorinated analogue. As in the case of the non-fluorinated analogue, Na⁺ acts as a co-catalyst with the fluorinated catalyst again yielding greater rates and total turnovers. Computational studies shed light on the possible mechanistic pathways. The initial alkane activation is a net Ir-H/C-H bond metathesis leading to formation of an Ir-alkyl bond and loss of H₂; this is the slowest chemical step in the cycle. The lowest energy pathway is calculated to proceed via concerted metalated deprotonation (CMD) of the alkane. Pathways proceeding via transition states with oxidative addition (Ir(V)) character, however, are calculated to be only slightly higher in energy. These transition states can lead either to Ir(V) intermediates, which then lose H₂, or connect directly to a dihydrogen complex. The role of Na⁺ is largely to promote dechelation by coordinating to an acetate oxygen, opening a vacant coordination site which allows reaction with the alkane. This coordination by Na⁺ prevents the CMD mechanism from operating, but it significantly lowers the energy of the Ir(V) TSs. NBO analysis shows a net transfer of charge from the alkane atoms to the metal complex in the Ir(V) TSs, with and without coordinated Na⁺. Thus the oxidative addition is actually reductive in nature, driven in part by electrophilicity of the metal center. The Na⁺ cation further increases electrophilicity in addition to promoting dechelation. The greater activity of the fluorinated catalyst compared with the parent complex can also be explained in terms of the electrophilic nature of the reaction. The fluorinated catalyst is also more resistant to decomposition than the non-fluorinated analogue.Ph.D.Includes bibliographical reference
Soluble starch-blended Ca2+-Zn2+-alginate composites-based microparticles of aceclofenac: Formulation development and in vitro characterization
No full textThe present article describes development of starch-blended Ca2+-Zn2+-alginate microparticles of aceclofenac for attaining gastric protection and controlled release delivery. Different formulations (F1 to F7) of microparticles were prepared by ionotropic gelation method and subjected to characterization studies. In vitro drug release studies were performed in 0.1 N HCl (pH 1.2) for initial 2 h and additional 5 h in phosphate buffer (pH 7.4). These microparticles were characterized by SEM, FTIR spectroscopy and XRD analyses. The formulation F7 (prepared using sodium alginate of 300 mg, soluble starch 250 mg, 5% CaCl2 and 1% ZnSO4) was selected as the optimized formulation, which exhibited entrapment efficiency of 85.73%, particle size of 1610 μm and viscosity of 802.16 cps. In vitro drug release from the formulation F7 revealed maximal 38% drug release within 7 h indicating sustained drug release profile from the prepared formulation. Also, in vitro swelling studies revealed maximal swelling within the period of 2 h at pH 7.4 for all these microparticles. The surface morphology studies performed using SEM showed smooth and spherical nature of the microparticles. Evaluation of drug release kinetic indicated fitting as per Korsmeyer-Peppas model and construed drug release via Fickian diffusion mechanism. Drug-excipient interaction studies using FTIR spectroscopy showed no change in characteristic peaks of the drug, while powder XRD revealed absence of sharp crystalline peaks of the drug. Overall, the present investigation corroborated successful development of microparticles of aceclofenac as an effective and cost-effective approach for oral delivery of aceclofenac. Keywords: Polymer composites, Ionotropic gelation, Microparticles, Drug release, Diffusion, Dissolutio
Soluble starch-blended Ca 2+ -Zn 2+ -alginate composites-based microparticles of aceclofenac: Formulation development and in vitro characterization
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