| 44491. |
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| 44492. |
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| 44493. |
- Sridhar, Praveen, et al.
(författare)
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Modeling Grinding Processes-Mesh or Mesh-Free Methods, 2D or 3D Approach?
- 2022
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Ingår i: Journal of Manufacturing and Materials Processing. - : MDPI. - 2504-4494. ; 6:5
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Tidskriftsartikel (refereegranskat)abstract
- The objectives of this study are mainly two: (1) to validate whether a single grain scratch process can be modeled in two dimensions under the assumption of plane strain, and (2) to select the best discretization approach to model a single grain scratch process. This paper first focuses on the simulation of the orthogonal cutting process (aluminum alloy A2024 T351) using two mesh-based discretization approaches, the pure Lagrangian method (LAG) and the arbitrary Lagrangian-Eulerian method (ALE), and two particle-based approaches, the particle finite element method (PFEM) and smooth particle hydrodynamics (SPH), for both positive and negative rake angles. Benchmarking of the orthogonal cutting models at a rake angle of gamma = 20 degrees is performed with the results of the process forces (cutting and passive forces) of a turning experiment from the literature. It is shown that all models are able to predict the cutting forces, but not the passive force. The orthogonal cutting model is further extended to simulate the cutting mechanism with negative rake tool geometries typically found in grinding and single grit scratching processes. The effects of the negative rake angles on the discretization approaches are studied. The calculated process forces are also compared to the measurements of the single grit scratch process performed at our laboratory. The 2D orthogonal cutting models significantly overestimate the process forces. One of the reasons why the orthogonal 2D cutting model is inadequate is that it cannot describe the complex mechanisms of material removal such as rubbing, plowing, and cutting. To account for these phenomena in LAG, ALE, and SPH discretization approaches, a 3D scratch model is developed. When comparing the process forces of the 3D model with the experimental measurements, all three discretization approaches show good agreement. However, it can be seen that the ALE model most closely matches the process forces with the experimental results. Finally, the ALE 3D scratch model was subjected to sensitivity analysis by changing the cutting speed, the depth of cut and the tool geometry. The results clearly show that the ALE method not only predicts the process forces and form the trends observed in the scratching experiments, but also predicts the scratch topography satisfactorily. Hence, we conclude that a 3D model is necessary to describe a scratch process and that the ALE method is the best discretization method.
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| 44494. |
- Srinivas, Jangirala, et al.
(författare)
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Designing Secure User Authentication Protocol for Big Data Collection in IoT-Based Intelligent Transportation System
- 2021
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Ingår i: IEEE Internet of Things Journal. - : IEEE. - 2327-4662. ; 8:9, s. 7727-7744
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Tidskriftsartikel (refereegranskat)abstract
- Secure access of the real-time data from the IoT smart devices (e.g., vehicles) by a legitimate external party (user) is an important security service for Big Data collection in Internet of Things (IoT)-based Intelligent Transportation System (ITS). To deal with this important issue, we design a new three-factor user authentication scheme, called UAP-BCIoT, which relies on Elliptic Curve Cryptography (ECC). The mutual authentication between the user and an IoT device happens via the semi-trusted Cloud-Gateway (CG) node in UAP-BCIoT. UAP-BCIoT supports several functionality features needed for IoT-based ITS environment including IoT smart device credential validation and Big Data analytics. A detailed security analysis is conducted based on the defined threat model to show that UAP-BCIoT is resilient against many known attacks. A thorough comparative study reveals that UAP-BCIoT supports better security, offers various functionality attributes, and also provides similar costs in communication as well computation as compared to other relevant schemes Finally, the practical demonstration of the proposed UAP-BCIoT is also provided to measure its impact on the network performance parameters.
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| 44495. |
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| 44496. |
- Srivastava, K., et al.
(författare)
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Molecular structure and hydrogen bond interactions of a paracetamol-4,4′-bipyridine cocrystal studied using a vibrational spectroscopic and quantum chemical approach
- 2018
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Ingår i: CrystEngComm. - : Royal Society of Chemistry. - 1466-8033. ; 20:2, s. 213-222
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of the current study is to perform the structural and spectroscopic characterization of paracetamol-4,4′-bipyridine (PRA-BPY) cocrystal using infrared, Raman spectroscopy and density functional theory (DFT) calculations. To reveal the interactions between PRA and BPY, two models (monomer and dimer + PRA) of a cocrystal are designed and optimized using DFT with a 6-311G (d, p) basis set. An atoms in molecule study shows that the non-covalent interactions in particular hydrogen bonds involved in forming the cocrystal are moderate in nature. Natural bond orbital analysis of the second order perturbation theory of the Fock matrix suggests that interactions LP (1) N13 → π∗(C15-O16) and LP (1) N56 → σ∗(N13-H14) are responsible for the stabilization of the molecule.
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| 44497. |
- Srivastava, Karnica, et al.
(författare)
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Molecular structure, spectroscopic signature and reactivity analyses of paracetamol hydrochloride monohydrate salt using density functional theory calculations
- 2019
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Ingår i: CrystEngComm. - : Royal Society of Medicine Press. - 1466-8033. ; 21:5, s. 857-865
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to understand the role of the intermolecular hydrogen bond interactions present in paracetamol hydrochloride monohydrated salt. Paracetamol hydrochloride monohydrate salt (PRA-HCl) and paracetamol (form I) were investigated via vibrational (FT-IR and FT-Raman) spectroscopy and density functional theory (DFT) to gain insight into the hydrogen bond patterns present in these crystalline materials. Two different density functionals, wB97X-D and M062X, were used for the comparison of the results. The geometrical parameters of PRA-HCl and form I obtained using these functional were compared with the crystallographic data, which proved the existence of intra-molecular and intermolecular hydrogen bonds. The C10O2 group of form I forms an intramolecular hydrogen bond, while the O1–H18 group of PRA-HCl forms an intermolecular hydrogen bond with a chloride ion (Cl−), resulting in the elongation of the bond length and shift to a lower wavenumber for the O1–H18 group. To examine the potency of hydrogen bonding, quantum theory of atoms in molecules (QTAIM) calculations were performed and the results suggested that O1–H18⋯Cl22 is a strong intermolecular hydrogen bond. The chemical reactivity parameters reveal that the PRA-HCl and PRA-OXA cocrystals are more reactive and softer (low HOMO–LUMO energy gap) in comparison to paracetamol (form I).
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| 44498. |
- Srivastava, Karnica, et al.
(författare)
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Vibrational analysis and chemical activity of paracetamol-oxalic acid cocrystal based on monomer and dimer calculations : DFT and AIM approach
- 2016
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 6:12, s. 10024-10037
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Tidskriftsartikel (refereegranskat)abstract
- The study of structural and spectral characteristics of a paracetamol-oxalic acid (PRA-OXA) cocrystal has been carried out using two models (monomer and dimer), with the aim to understand the supramolecular structure and intramolecular interactions within the cocrystal. The cocrystal has been characterized by infrared and Raman spectroscopy combined with quantum chemical calculations molecular electrostatic potential surface (MEPS), frontier orbital analysis and electronic reactivity descriptors were used to understand the role of interactions involved in affecting the chemical reactivity of individual molecules in the cocrystal. It is observed that the C=O, N-H and O-H groups of paracetamol are involved in hydrogen bonds to form cocrystals. NBO analysis suggests that the two types of interactions LP(1)(N8) -> pi*(C9-O10) and LP(2)(O10) -> sigma*(O25-H28) are responsible for the stability of the molecule. AIM analysis suggested that the non-covalent interactions are moderate in nature. The calculated HOMO-LUMO energies reveal that the charge transfer occurs within the cocrystal. Chemical reactivity parameters show that the cocrystal is more active than paracetamol.
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| 44499. |
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| 44500. |
- Srivastava, Vaibhav, et al.
(författare)
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Alternative splicing studies of the reactive oxygen species gene network in Populus reveal two isoforms of high-isoelectric-point superoxide dismutase
- 2009
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Ingår i: Plant Physiology. - : Oxford University Press (OUP). - 0032-0889 .- 1532-2548. ; 149:4, s. 1848-1859
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Tidskriftsartikel (refereegranskat)abstract
- Recent evidence has shown that alternative splicing (AS) is widely involved in the regulation of gene expression, substantially extending the diversity of numerous proteins. In this study, a subset of expressed sequence tags representing members of the reactive oxygen species gene network was selected from the PopulusDB database to investigate AS mechanisms in Populus. Examples of all known types of AS were detected, but intron retention was the most common. Interestingly, the closest Arabidopsis (Arabidopsis thaliana) homologs of half of the AS genes identified in Populus are not reportedly alternatively spliced. Two genes encoding the protein of most interest in our study (high-isoelectric-point superoxide dismutase [hipI-SOD]) have been found in black cottonwood (Populus trichocarpa), designated PthipI-SODC1 and PthipI-SODC2. Analysis of the expressed sequence tag libraries has indicated the presence of two transcripts of PthipI-SODC1 (hipI-SODC1b and hipI-SODC1s). Alignment of these sequences with the PthipI-SODC1 gene showed that hipI-SODC1b was 69 bp longer than hipI-SODC1s due to an AS event involving the use of an alternative donor splice site in the sixth intron. Transcript analysis showed that the splice variant hipI-SODC1b was differentially expressed, being clearly expressed in cambial and xylem, but not phloem, regions. In addition, immunolocalization and mass spectrometric data confirmed the presence of hipI-SOD proteins in vascular tissue. The functionalities of the spliced gene products were assessed by expressing recombinant hipI-SOD proteins and in vitro SOD activity assays.
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