Passive vibration isolation of reaction wheel disturbances using a low frequency flexible space platform

Reaction wheel assemblies (RWAs) are momentum exchange devices used in fine pointing control of spacecrafts. Even though the spinning rotor of the reaction wheel is precisely balanced to minimize emitted vibration due to static and dynamic imbalances, precision instrument payloads placed in the neighborhood can always be severely impacted by residual vibration forces emitted by reaction wheel assemblies. The reduction of the vibration level at sensitive payloads can be achieved by placing the RWA on appropriate mountings. A low frequency flexible space platform consisting of folded continuous beams has been designed to serve as a mount for isolating a disturbance source in precision payloads equipped spacecrafts.Analytical and experimental investigations have been carried out to test the usefulness of the low frequency flexible platform as a vibration isolator for RWAs. Measurements and tests have been conducted at varying wheel speeds, to quantify and characterize the amount of isolation obtained from the reaction wheel generated vibration. These tests are further extended to other variants of similar design in order to bring out the best isolation for given disturbance loads. Both time and frequency domain analysis of test data show that the flexible beam platform as a mount for reaction wheels is quite effective and can be used in spacecrafts for passive vibration control.     

Ferrocene conjugated copper(II) complexes of terpyridine and traditional Chinese medicine (TCM) anticancer ligands showing selective toxicity towards cancer cells

Six novel mixed‐ligand copper(II) complexes, namely, [Cu(R‐tpy)(L)]NO₃ ( 1–6 ), where R‐tpy is 4′‐phenyl‐2,2′:6′,2′′‐terpyridine (Ph‐tpy; 1–3 ) and 4′‐ferrocenyl‐2,2′:6′,2′′‐terpyridine (Fc‐tpy; 4–6 ), L is the bidentate O,O donor monoanion of plumbagin (5‐hydroxy‐2‐methyl‐1,4‐naphthoquinone; plum in 1 , 4 ), chrysin (5,7‐dihydroxyflavone; chry in 2 , 5 ) and curcumin (bis(4‐hydroxy‐3‐methoxyphenyl)‐1,6‐diene‐3,5‐dione; curc in 3 , 6 ) have been synthesized and characterized and their in vitro cytotoxicity against cancer cells is evaluated. The energy optimized structures and the frontier orbitals of the complexes have been obtained from the DFT calculations. Complexes 4–6 with a conjugated ferrocenyl moiety and TCM anticancer ligands, namely, plum (in 4 ), chry (in 5 ) and curc (in 6 ) showed potent cytotoxicity giving respective IC₅₀ values of 1.2 μM, 0.62 μM and 0.21 μM in HeLa and 2.0 μM and 1.0 μM and 0.34 μM in MCF‐7 cancer cells while being much less toxic to MCF‐10A normal cells (IC₅₀: 8.3‐17.1 μM). In contrast, complexes 1–3 with a conjugated phenyl moiety were appreciably less toxic to HeLa cells with respective IC₅₀ values of 10.4 μM, 8.1 μM and 5.5 μM when compared with their ferrocenyl analogues 4–6 . Mechanistic studies using Hoechst staining and Annexin‐V‐FITC assays on cancer cells revealed an apoptotic pathway of cell death induced by the complexes. Fluorescence imaging study showed that complex 6 having curcumin as ligand localized primarily in the mitochondria of HeLa cells. Thus, we demonstrate in this study that ferrocene conjugation to copper(II) complexes of TCM anticancer ligands significantly increases the selectivity and cytotoxicity of the resulting complexes towards cancer cells over normal cells.     

Synthesis of Terminal Oligosaccharides from Type Specific Lipooligosaccharide of Mycobacterium Tuberculosis

Abstract

The coupling reaction between 1,3-di-O-acetyl-4-O-benzyl-2-O-methyl-α-L-rhamnopyranose (9) and methyl 4-O-benzyl-2-O-methyl-α-L-rhamno-pyranoside (4) was carried out in the presence of boron trifluoride-etherate followed by deacetylation to give the disaccharide (11) containing a free 3′ position. The second glycosylation reaction with 2,3,4,6-tetra-O-acetyl-α-d-glucopyranosyl bromide in the presence of mercuric salts followed by removal of benzyl and acetyl groups provided the trisaccharide 2. The boron trifluoride catalysed condensation of 1,3,4-tri-O-acetyl-2-O-methyl-L-fucopyranose (14) and methyl 2,4,6-tri-O-benzyl-α-d-glucopyranoside (15) gave the disaccharide (16) from which the protecting groups were removed to form the disaccharide (3).     

Synthesis of Hydrophenanthbene Derivatives Related to Diterpenes Involving Reductive Methylation of Aromatic Ketones

The tricyclic ketones 13 and 14, prepared from naphthalene and 2-methoxynaphthalene respectively, were subjected to reductive methylation in anhydrous ammonia to provide the β, γ -unsaturated ketones 16 and 17 in high yield which were stereoselectively converted into the A/B trans-fused compounds 3 and 4 respectively.     

Quinolinephosphomolybdate as ion exchanger: synthesis,characterization, and application in separation of <Superscript>90</Superscript>Y from <Superscript>90</Superscript>Sr

An inorganic ion exchanger, quinolinephosphomolybdate has been synthesized and characterized by elemental analysis, infrared (IR) and X-ray diffraction (XRD) spectroscopy. This compound is highly stable toward thermal, chemical and radiation dose. This has been employed in the separation of carrier-free ⁹⁰Y from its parent ⁹⁰Sr from an equilibrium mixture. The absorbed daughter was recovered by using 0.0284 mol L⁻¹ ascorbic acid solutions at pH 5.0 as eluting agent.     

Differential flexibility of the secondary structures of lysozyme and the structure and ordering of surrounding water molecules

We have performed an atomistic molecular dynamics simulation of an aqueous solution of hen egg-white lysozyme at room temperature with explicit water molecules. Several analyses have been carried out to explore the differential flexibility of the secondary structural segments of the protein and the structure and ordering of water around them. It is found that the overall flexibility of the protein molecule is primarily controlled by few large-amplitude bistable motions exhibited by two coils; one connecting two α-helical segments in domain-1 and the other connecting a 3(10) helix and a β-sheet in domain-2 of the protein. The heterogeneous structuring of water around the segments of the protein has been found to depend on the degree of exposure of the segments to water. The ordering of water molecules around the protein segments and their tagged potential energies have been found to be anticorrelated with each other. Some of these findings can be verified by suitable experimental studies.     

A case study in ultracold reactive scattering: D + H2

We report theoretical results for reaction and vibrational quenching of the ultracold collision D + H(2) (v, j = 0) for a wide range of initial vibrationally excited states v. The v-dependence of the zero-temperature limit of the reaction rate coefficient shows two distinct regimes: a barrier dominated regime for 0 ≤ v ≤ 4, and a barrierless regime for v ≥ 5. We also present detailed distributions over the rovibrational states of the products. We find an approximate conservation of the internal vibrational energy; namely, the branching ratios always favor the highly excited final states, which have vibrational energies similar to that of the entrance channel.     

On the Three-Dimensional Central Moment Lattice Boltzmann Method

A three-dimensional (3D) lattice Boltzmann method based on central moments is derived. Two main elements are the local attractors in the collision term and the source terms representing the effect of external and/or self-consistent internal forces. For suitable choices of the orthogonal moment basis for the three-dimensional, twenty seven velocity (D3Q27), and, its subset, fifteen velocity (D3Q15) lattice models, attractors are expressed in terms of factorization of lower order moments as suggested in an earlier work; the corresponding source terms are specified to correctly influence lower order hydrodynamic fields, while avoiding aliasing effects for higher order moments. These are achieved by successively matching the corresponding continuous and discrete central moments at various orders, with the final expressions written in terms of raw moments via a transformation based on the binomial theorem. Furthermore, to alleviate the discrete effects with the source terms, they are treated to be temporally semi-implicit and second-order, with the implicitness subsequently removed by means of a transformation. As a result, the approach is frame-invariant by construction and its emergent dynamics describing fully 3D fluid motion in the presence of force fields is Galilean invariant. Numerical experiments for a set of benchmark problems demonstrate its accuracy.     

Reactive chemical dynamics through conical intersections

Reaction dynamics of prototypical, D + H₂ and Cl (²P) + H₂, chemical reactions occurring through the conical intersections of the respective coupled multi-sheeted potential energy surfaces is examined here. In addition to the electronic coupling, nonadiabatic effects due to relativistic spin-orbit coupling are also considered for the latter reaction. A time-dependent wave packet propagation approach is undertaken and the quantum dynamical observables viz., energy resolved reaction probabilities, integral reaction cross-sections and thermal rate constants are reported.