Bromination of 2,2′-anhydrouridine

When 2,2′-anhydrouridine (1) is treated with aqueous Br₂, cleavage of the pyrimidine ring occurs and the 2-amino-oxazoline (2) as well as its corresponding 2-oxo-analogue (3) is formed, the structure of which was proved by investigating their acetylated derivatives, (4 and 5). Bromination of 1 in the absence of water yields the 2′,5-dibromo-uridine (6) which can be converted into the corresponding 2,2′-anhydro-derivative (7). Structures were proved by MS, NMR and IR.     

Synthesis and Stereostructure of Saturated Isoindolone-Fused Hetero Tri-, Tetra-, and Pentacyclic Compounds

t-2-Benzoyl-t-4-phenylcyclohexane-r-1-carboxylic acid reacts with hydrazine to give the saturated 1,7-diphenyl-trans-phthalazin-4(3H)-one. The reaction of the acid with ethylenediamine yields diastereomeric trans-imidazo[2,3-a]isoindoles, which differ in their C-1 configuration. The cyclizations of the acid with cis-2-aminocyclohexane- or 4-cyclohexenemethanol result in trans-isoindolo[2,1-a][3,1]benzoxazines, while in its reactions with the analogous di-endo- and di-exo-norbornane- and -norborneneamino alcohols, the acid gives methylene-bridged isomeric di-endo-norbornanes or a norbornene derivative; the corresponding diastereomeric di-exo derivatives have also been prepared. After isolation, the structures were established by means of ¹H and ¹³C NMR spectroscopy, with application of DIFFNOE, DEPT, HMQC, HMBC, and 2D-COSY techniques.     

Ring transformations of β-lactam-condensed 1,3-benzothiazines to isoquinoline and thiazole derivatives by sulfur extrusion and addition sequences

The ring transformations of dichloro-β-lactam-fused 2-aryl-1,3-benzothiazines with sodium methoxide were investigated. With 2 equiv of base, the dichloro-β-lactam derivatives underwent rearrangement and dihydro-1,4-benzothiazepines, 3,4-substituted isoquinolines and substituted thiazole disulfides were isolated. A possible reaction mechanism is proposed for the simultaneous formation of the novel products. The formation of isoquinoline and thiazole derivatives can be explained by sulfur extrusion and addition sequences.     

Micromagnetic modeling studies on the effects of stress on magnetization reversal and dynamic hysteresis

The complex behaviors of magnetic materials subjected to magneto-electro-mechanical coupled fields call for a better understanding of the mechanism of multi-fields coupling. In this paper, micromagnetic modeling is carried out to study the effect of stress on hysteresis loops and dynamic magnetization reversal. The time-dependent Landau–Lifshitz–Gilbert equation which governs the evolution of magnetization is solved using the fast Fourier transform technique in reciprocal space. The simulation results show that the stress changes the distribution of easy directions and, therefore, leads to the change of magnetic properties. Moreover, the positive product of the stress and saturation magnetostriction coefficients increases the coercivity, hence, increases the area enclosed by the hysteresis loop. A stress-induced magnetization reversal is investigated.     

Numerical simulation of free shear flows and far-field sound pressure directivity

An implicit spatial differencing technique with fourth-order accuracy has been developed based on the Pade compact scheme. A dispersion-relation-preserving concept has been incorporated into the numerical scheme. Two-dimensional Euler computation of a spatially developing free shear flow with and without external excitation has been performed to demonstrate the capability of the numerical scheme developed. Results are in good agreement with theory and experimental observation regarding the growth rate of the fluctuating velocity, the convective velocity and the vortex-pairing process. The far-field sound pressure generated by the computed shear flow solution using Lighthill's acoustic analogy shows a strong directivity with a zone of silence at the flow angle.     

Synthesis of 4,5-dihydro-1,4-benzothiazepine derivatives via ring expansion

Basic treatment in methanol of a chloro-β-lactam fused with dihydrobenzothiazine led to the corresponding 1,4-benzothiazepine derivative via a new ring expansion. The structure of the product, deduced from IR and ¹H NMR data, was confirmed by X-ray measurements.     

Laser-induced vibrations of micro-beams under different boundary conditions

In this study, the vibration phenomenon during pulsed laser heating of a micro-beam is investigated. The beam is made of silicon and is heated by a non-Gaussian laser beam with a pulse duration of 2 ps, which incites vibration due to the thermoelastic damping effect. The coupling between the temperature field and stress field induces energy dissipation and converts mechanical energy into heat energy, which is irreversible. An analytical–numerical technique based on the Laplace transform is used to calculate the vibration of the deflection and thermal moment. A general algorithm of the inverse Laplace transform is developed. The validation of this algorithm is obtained through comparison with numerical results obtained by the FEMLAB software package. The effect of laser pulse energy absorption depth is studied. The size effect and the effect of different boundary conditions are also analyzed. Finally, the damping ratio and resonant frequency shift ratio of beams due to the air damping effect and the thermoelastic damping effect are compared.