Opto-thermal behavior of polypropylene fibres using a modified hot-stage attached to the interference microscope

The influence of temperature on the optical and structural properties of three samples of polypropylene fibres (having different deniers) has been studied over the temperature range (28–67^oC). A hot-stage attached with the Pluta microscope has been modified for this purpose. The effect of temperature on the refractive indices (n, n), the mean polarizabilities per unit volume (P^ll, P) and the optical orientation function f(θ) have been investigated for each sample. The thermal coefficients of the refractive indices were determined. The refractive index profiles are also provided at different temperatures for each of the three tested samples. Microinterferograms are given for illustration.     

On chained overrings of pseudo-valuation rings

A prime ideal P of a commutative ring R with identity is called strongly prime if aP and bR are comparable for every a, b in R. If every prime ideal of R is strongly prime, then R is called a pseudo-valuation ring. It is well-known that a (valuation) chained overring of a Prufer domain R is of the form R_P for some prime ideal P of R.In this paper, we show that this statement is valid for a certain class of chained overrings of a pseudo-valuation ring.     

Transesterification of Methylbenzoate with Alcohols Catalyzed by Natural Phosphate

Transesterification of methylbenzoate with various alcohols was catalyzed by natural phosphate with or without solvent in heterogeneous media. The molar ratio of alcohol/ester, solvent effect, and weight of catalyst effect have been studied. We have found that the nature of alcohol and the reaction temperature play an important role in the transesterification process. The catalyst can be regenerated and reused without lost of activity.     

Theoretical studies on the bifunctionality of chiral thiourea-based organocatalysts: competing routes to C-C bond formation

The mechanism of enantioselective Michael addition of acetylacetone to a nitroolefin catalyzed by a thiourea-based chiral bifunctional organocatalyst is investigated using density functional theory calculations. A systematic conformational analysis is presented for the catalyst, and it is shown that both substrates coordinate preferentially via bidentate hydrogen bonds. The deprotonation of the enol form of acetylacetone by the amine of the catalyst is found to occur easily, leading to an ion pair characterized by multiple H-bonds involving the thiourea unit as well. Two distinct reaction pathways are explored toward the formation of the Michael product that differ in the mode of electrophile activation. Both reaction channels are shown to be consistent with the notion of noncovalent organocatalysis in that the transition states leading to the Michael adduct are stabilized by extensive H-bonded networks. The comparison of the obtained energetics for the two pathways allows us to propose an alternative mechanistic rationale for asymmetric C-C bond forming reactions catalyzed by bifunctional thiourea derivatives. The origin of enantioselectivity in the investigated reaction is also discussed.     

Solvent tuning of the substitution behavior of a seven-coordinate iron(III) complex

A detailed kinetic study of the substitution behavior of the seven-coordinate [Fe(dapsox)(L)2]ClO4 complex (H(2)dapsox = 2,6-diacetylpyridine-bis(semioxamazide), L = solvent or its deprotonated form) with thiocyanate as a function of the thiocyanate concentration, temperature, and pressure was undertaken in protic (EtOH and acidified EtOH and MeOH) and aprotic (DMSO) organic solvents. The lability and substitution mechanism depend strongly on the selected solvent (i.e., on solvolytic and protolytic processes). In the case of alcoholic solutions, substitution of both solvent molecules by thiocyanate could be observed, whereas in DMSO only one substitution step occurred. For both substitution steps, [Fe(dapsox)(L)2]ClO4 shows similar mechanistic behavior in methanol and ethanol, which is best reflected by the values of the activation volumes (MeOH DeltaV(I) = +15.0 +/- 0.3 cm(3) mol(-1), DeltaV(II) = +12.0 +/- 0.2 cm(3) mol(-1); EtOH DeltaV(I) = +15.8 +/- 0.7 cm(3) mol(-1), DeltaV(II) = +11.1 +/- 0.5 cm(3) mol(-1)). On the basis of the reported activation parameters, a dissociative (D) mechanism for the first substitution step and a D or dissociative interchange (I(d)) mechanism for the second substitution step are suggested for the reaction in MeOH and EtOH. This is consistent with the predominant existence of alcoxo [Fe(dapsox)(ROH)(OR)] species in alcoholic solutions. In comparison, the activation parameters for the substitution of the aqua-hydroxo [Fe(dapsox)(H2O)(OH)] complex by thiocyanate at pH 5.1 in MES were determined to be DeltaH = 72 +/- 3 kJ mol(-1), DeltaS = +38 +/- 11 J K(-1) mol(-1), and DeltaV = -3.0 +/- 0.1 cm(3) mol(-1), and the operation of a dissociative interchange mechanism was suggested, taking the effect of pressure on the employed buffer into account. The addition of triflic acid to the alcoholic solutions ([HOTf] = 10(-3) and 10(-2) M to MeOH and EtOH, respectively) resulted in a drastic changeover in mechanism for the first substitution step, for which an associative interchange (Ia) mechanism is suggested, on the basis of the activation parameters obtained for both the forward and reverse reactions and the corresponding volume profile. The second substitution step remained to proceed through an I(d) or D mechanism (acidified MeOH DeltaV(II) = +9.2 +/- 0.2 cm(3) mol(-1); acidified EtOH DeltaV(II) = +10.2 +/- 0.2 cm(3) mol(-1)). The first substitution reaction in DMSO was found to be slowed by several orders of magnitude and to follow an associative interchange mechanism (DeltaS = -50 +/- 9 J K(-1) mol(-1), DeltaV(I) = -1.0 +/- 0.5 cm(3) mol(-1)), making DMSO a suitable solvent for monitoring substitution processes that are extremely fast in aqueous solution.     

Cembranoid diterpenes and a briarane diterpene from corals

Two new cembrane diterpenes (+)-polydactylide (1) and (+)-7alpha,8beta-dihydroxydeepoxysarcophine (2) together with (+)-sarcophine (3) and (+)-sarcophytoxide (4) have been isolated from the soft coral Sinularia polydactyla. The new cembrane diterpene (-)-7beta-hydroxy-8alpha-methoxydeepoxysarcophine (5) has been obtained from the soft coral Sarcophyton trocheliophorum and the known briarane diterpene briaexcavatolide W (6) from the gorgonian coral Briareum sp.The structures were determined primarily by NMR spectroscopy. The assignment of NMR signals was performed by means of (1)H-(1)H COSY, ROESY, HMQC and HMBC experiments.     

On line interferometric investigation of the neck propagation phenomena of stretched polypropylene fibre

On line interferometric investigation of the neck propagation phenomenon of stretched fibre is carried out using an automatic multiple-beam Fizeau fringes technique. It was observed that under such a deformation condition, a neck deformation is formed and propagated steadily towards the gripped ends of the stretched sample. The neck propagation was recorded carefully during the course of the tests by means of a CCD camera. The fringe shift profile due to the neck formation was analyzed during the propagation stage. A polypropylene (PP) sample was stretched until a neck deformation is formed at room temperature. The 3D time-refractive index profile is investigated to clarify the fixed profile of propagation. The obtained microinterferograms are clarifying the fixed neck profile during the propagation of necking phenomena. The speed of neck propagation was calculated. The dependence of the propagation on the drawing speed and draw ratio was investigated.     

Achieving large uniform tensile ductility in nanocrystalline metals

Synchrotron x-ray diffraction and high-resolution electron microscopy revealed the origin of different strain hardening behaviors (and dissimilar tensile ductility) in nanocrystalline Ni and nanocrystalline Co. Planar defect accumulations and texture evolution were observed in Co but not in Ni, suggesting that interfacial defects are an effective passage to promote strain hardening in truly nanograins. Twinning becomes less significant in Co when grain sizes reduce to below ~15 nm. This study offers insights into achieving excellent mechanical properties in nanocrystalline materials.     

Minimization of scintillation index against displacement parameters

For sinusoidal beams, minimization of scintillation index is carried out against the displacements parameters. It is found that x-y asymmetric cosh-Gaussian beam fulfills the requirements of such optimum beam. Our minimization procedure reveals that the optimum beam is achieved by continually focusing it at the chosen propagation length and by further adjusting displacements parameters to be propagation distance dependent. Scintillation index of thus constructed optimum beam is formulated and numerically evaluated. Our graphical comparisons entailing collimated and focused versions of cos-, cosh-Gaussian, annular-Gaussian and Gaussian beams show that the optimum beam yields the lowest scintillations provided that propagation range is less than or equal to the focusing distance.