Mossbauer Spectroscopic Study of Gamma Irradiation on the Structural Properties of Hematite, Magnetite and Limonite Concrete for Nuclear Reactor Shielding

This work investigate the effect of gamma irradiation on a heavy type of concrete, constructed for nuclear reactor shield. The effect of gamma irradiation was studied after annealing the concrete samples at 300°C for 24 hours in air. This revised version was published online in August 2006 with corrections to the Cover Date.     

TFAA chemical derivatization and XPS. Analysis of OH and NHx polymers

The determination of functional groups on complex polymer surfaces by X‐ray photoelectron spectroscopy (XPS) can be improved considerably by derivatization reactions. Simple polymers containing hydroxyl groups or amino groups were investigated as reference materials for the derivatization with trifluoroacetic anhydride (TFAA). ‐1 Poly(vinyl alcohol) (PVA), poly(hydroxyethyl methacrylate) (PHEMA), poly(vinyl butyral) (PVB), poly(allylamine) (PAAm), and poly(diallyl amine) (PDAAm) were derivatized using TFAA and analyzed with XPS. Polyethylene (PE) was used as an independent external reference for the binding energy (BE). Applying this procedure, the BE scales of all measurements were referenced to the carbon atoms of PE. It was found that the BE of the CF₃ component in the C1s region is different when bonded as an acetate or as an amide. The CF₃ BE is also influenced by the density of these groups in the polymer molecule. In TFAA‐PVA, where every second main chain carbon atom carries a trifluoroacetate (TFAc) group, the BE is 294.3 eV while in TFAA‐PVB with only isolated groups, the BE is 293.6 eV. The BE of the CF₃ component in the trifluoroacetamides (TFAAms) prepared from PAAm and PDAAm was found to be 292.5 and 292.3 eV, respectively. Compared with the analog fluorine free compounds, the BE is shifted toward higher values also for the ester carbon atom, the amide carbon atom, and the carbon atom to which the ester or amide is bonded. The data suggest that the gas phase reaction of TFAA with a polymer surface is diffusion limited. The actual ester or amide formation is a fast reaction and runs as a wave into the surface. Copyright © 2009 John Wiley & Sons, Ltd.     

Vibration suppression of a time-varying stiffness AMB bearing to multi-parametric excitations via time delay controller

The applications of active magnetic bearings are growing in industry due to its amazing advantages in reducing friction losses. In this research, the vibration of a two-degree-of-freedom rotor, active magnetic bearings system is suppressed via a nonlinear time delay controller at the confirmed worst resonance case. The selected resonance case is the simultaneous primary and sub-harmonic resonance case. The main aim of this paper was to study the effects of the nonlinear, time delay controller on the behavior of the vibrating system. The multiple time scale perturbation technique is applied to obtain an approximate solution to the second-order approximation. The steady-state solution is obtained around the worst resonance case. The stability of the system is studied applying both frequency response equations and phase-plane method. The worst resonance case is confirmed applying numerical technique. The effects of the different parameters on the steady-state response of the vibrating system are investigated. The obtained approximate solution is validated numerically. Some recommendations are given regarding the design of such system. At the end of the work, a comparison is made with the available published work.     

Vibration reduction of a nonlinear spring pendulum under multi external and parametric excitations via a longitudinal absorber

The vibration of a ship pitch-roll motion described by a non-linear spring pendulum system (two degrees of freedom) subjected to multi external and parametric excitations can be reduced using a longitudinal absorber. The method of multiple scale perturbation technique (MSPT) is applied to analyze the response of this system near the simultaneous primary, sub-harmonic and internal resonance. The steady state solution near this resonance case is determined and studied applying Lyapunov’s first method. The stability of the system is investigated using frequency response equations. Numerical simulations are extensive investigations to illustrate the effects of the absorber and some system parameters at selected values on the vibrating system. The simulation results are achieved using MATLAB 7.0 programs. Results are compared to previously published work.     

Mössbauer and ESR investigation of the behaviour of iron in vanadium borophosphate glasses

Mössbauer and ESR measurements were performed on vanadium borophosphate glasses containing iron. The glass composition was 78 mole% V₂O₅, 15 mole% P₂O₅, 7 mole% B₂O₃ and different amounts of Fe₂O₃ (0.5–50 mole%) were added. The relative percentage of iron in different states and site positions could be determined for each glass composition. Correlation between the behaviour of iron and its variation in structural units and other physical properties are proposed. A maximum amount of 33 mole% Fe₂O₃ could be incorporated in the glass network, higher concentrations lead to the precipitation of α-Fe₂O₃.     

Core-valence correlation effects in calcium hydride

Accurate multi-reference contracted CI calculations have been performed on CaH to determine the bond distance and the dissociation energy. At the Hartree-Fock limit a bond distance 0.10 au longer than in experiments is found. This value is not improved by a valence CI calculation. Including the core-valence (CV) contribution to the correlation energy makes the bond distance too short by 0.06 au, and agreement with experiments is obtained first when the core-core (CC) contribution from the 3p orbitals is added also. It turns out that the only orbital which needs to be treated of the core is the 3p σ orbital, which shows some bonding character at the CI level. Tight d functions to describe a 3d orbital of the type occupied in the ²D state of Ca^?, and f functions to correlate the 3p orbital are necessary for obtaining a good bond distance. For the dissociation energy a different trend is observed with excellent agreement with experiments at the CV level and no improvement over the SCF level at the CC level. The results are discussed and analyzed in detail in the text, where a section on size consistency is also added.     

Mössbauer,X-ray and derivatographic studies on Egyptian Nile clay

The constituents of the clay minerals in eighteen Nile clay and two Desert (calcareous) samples, were investigated. The physicochemical transformations induced in the iron containing phases were followed by heat treatment. A conclusion was reached about the behaviour of the ferrous and ferric ions at various temperatures. This behabviour is applied to characterize the archaeological Ancient Egyptian pottery.     

Reduction of elastic stress concentrations in end-milled keyed connections

Frozen-stress, three-dimensional models were used to study the elastic stress distribution in both metric and inch rectangular, parallel, standard keys, shafts and hubs with end-milled keyways, loaded in torsion. The coefficient of friction between the shaft and the hub was measured and the surface conditions were arranged to simulate typical prototype friction. Positions and magnitudes of the peak shear stresses were determined in the prismatic part and at the ends of keys and keyways. The axial position of torque application to the hub, the key length and key-end shape were altered to investigate their effects on the stress distributions. The maximum shear stresses in the shaft occur in the keyway end if the key is not chamfered. The maximum stress in the standard metric shaft is 25 percent greater than in the inch standard. Changing the axial position of torque application from the middle to the front increases the peak stresses by about 13 percent. Doubling the length of hub and key reduces the stresses by about 25 percent. Filing off parts of the key to prevent contact at the keyway end reduces the maximum stresses by 11 percent.     

Isolation and In Silico Anti-SARS-CoV-2 Papain-Like Protease Potentialities of Two Rare 2-Phenoxychromone Derivatives from Artemisia spp.

Two rare 2-phenoxychromone derivatives, 6-demethoxy-4`-O-capillarsine (1) and tenuflorin C (2), were isolated from the areal parts of Artemisia commutata and A. glauca, respectively, for the first time. Being rare in nature, the inhibition potentialities of 1 and 2 against SARS-CoV-2 was investigated using multistage in silico techniques. At first, molecular similarity and fingerprint studies were conducted for 1 and 2 against co-crystallized ligands of eight different COVID-19 enzymes. The carried-out studies indicated the similarity of 1 and 2 with TTT, the co-crystallized ligand of COVID-19 Papain-Like Protease (PLP), (PDB ID: 3E9S). Therefore, molecular docking studies of 1 and 2 against the PLP were carried out and revealed correct binding inside the active site exhibiting binding energies of −18.86 and −18.37 Kcal/mol, respectively. Further, in silico ADMET in addition to toxicity evaluation of 1 and 2 against seven models indicated the general safety and the likeness of 1 and 2 to be drugs. Lastly, to authenticate the binding and to investigate the thermodynamic characters, molecular dynamics (MD) simulation studies were conducted on 1 and PLP.     

A Facile Access to Some New Pyrazole, 1,3,4-Thiadiazole,and Thiophene Derivatives via β-Ketosulfones

3-Bromoacetyl-1,5-diphenyl-1H-pyrazole-4-carbonitrile (1) reacts with sodium benzenesulfinate to give the corresponding ketosulfone 2. Treatment of 2 with hydrazonoyl chlorides 3a,b gives the 3,3′-bipyrazoles 5a,b. Ketosulfone 2 reacts also with arylidenemalononitriles to give the pyrazolylpyridones 10a,b. The reaction of compound 2 with phenylisothiocyanate and potassium hydroxide and treating intermediate with hydrazonoyl halides and with α-haloketones gives the 1,3,4-thiadiazoles 18a–c and thiophenes 21a–f, respectively.