Uncatalyzed and solvent-free multicomponent process for the synthesis of biphenyl-2-carbonitrile derivatives

An innovative route to prepare a number of variously substituted new biphenyl derivatives is presented here. The protocol avoids the use of a catalyst, an organic solvent, and dry conditions. [reaction: see text]     

Nanocrystalline magnetic PrFeCrB alloys

Ribbons of Pr₅Fe_77−xCr_xB₁₈ (x=0$x=0$, 1, 2, 2.5, 3, 4, 5) were produced by melt spinning and then annealed to develop an enhanced-remanence nanocrystalline magnetic material. These nanocomposites with Cr present a coercive field at least 50% higher than the Cr-free ones, which makes them promising materials for bonded magnets. Four different types of annealing were used in order to develop the nanocrystalline state and to optimize the magnetic properties of these alloys. The first was a conventional annealing, where the ribbons were wrapped in a tantalum foil and annealed in an argon atmosphere, but not encapsulated. The second was a flash annealing, where the ribbons were annealed by passing a current through them. The third was a conventional annealing in an external magnetic field. Finally, the fourth was a conventional annealing, where the ribbons were wrapped in a tantalum foil and encapsulated in quartz tubes with argon gas and then annealed. The annealed samples were studied by magnetic measurements, X-ray diffraction, scanning and transmission electron microscopy and atomic force microscopy. The best magnetic properties are found for Pr₅Fe₇₄Cr₃B₁₈, annealed by the fourth method, which resulted in the lowest oxygen content in the annealed nanocrystalline material as confirmed by scanning electron microscopy. The value for the coercive field for this composition is at least 50% higher than for the material without Cr (≈560 vs. ≈320 kA/m) and 40% higher than for the Nd₂Fe₁₄B/Fe₃B nanocomposite with Cr. Curie temperature measurements and X-ray diffraction data showed that the main phases present in all the samples are Pr₂Fe₁₄B, Fe₃B and α-Fe, Pr₂Fe₁₄B being the majoritary phase. From Curie temperature measurements it was also found that Cr atoms preferentially dissolve in the Fe₃B phase.     

Absence of Embedded Mass Shells: Cerenkov Radiation and Quantum Friction

We show that, in a model where a non-relativistic particle is coupled to a quantized relativistic scalar Bose field, the embedded mass shell of the particle dissolves in the continuum when the interaction is turned on, provided the coupling constant is sufficiently small. More precisely, under the assumption that the fiber eigenvectors corresponding to the putative mass shell are differentiable as functions of the total momentum of the system, we show that a mass shell could exist only at a strictly positive distance from the unperturbed embedded mass shell near the boundary of the energy–momentum spectrum.     

流体力学半径对估算胶体微球聚集速率常数的影响

胶体粒子聚集速率常数实验值远低于理论值一直是被普遍关注的问题.聚集速率常数的理论推导是基于粒子的几何半径来考虑的,但决定粒子扩散速率及聚集速率的应该是粒子的流体力学半径(大于几何半径),因而它是使聚集速率常数实验值低于理论值的因素之一.影响流体力学半径的因素很多,其中,带电粒子在溶液中因表面存在双电层,会明显增大流体力学半径,造成聚集速率减慢.而双电层的厚度又随溶液中离子强度的不同而改变.本工作在聚集速率的公式中引入了修正因子,即几何半径与其流体力学半径之比,以修正由于用几何半径代替流体力学半径带来的误差.其中几何半径和流体力学半径可以分别用扫描电镜(SEM)和动态光散射(DLS)来测定.以两种粒径的聚苯乙烯带电微球为例,考察了在不同离子强度下,该误差的大小.结果发现,对于半径为30 nm的微球,用流体力学半径计算的慢聚集速率常数比理论值偏低约8%.该误差随离子强度增加而减少.对于快聚集情况,流体力学半径对聚集速率基本没有影响.     

Synthesis of 2-Cycloalkenones (Parts of 1,4-Diacyl-1,3-butadiene Systems) and of a Heterocyclic Analogue by Metal-Catalyzed Decomposition of 2-Diazoacylfurans

Furans with side-chains at C(2) of various lengths terminating in diazomethyl keto groups are shown to undergo Rh₂(OAc)₄-catalyzed furan unravelling with the production of 2-cyclopentenone, 2-cyclohexenone, and 2-cycloheptenone to each of whose olefinic C(β) is attached an acrylaldehyde unit. Interposition of a cyclohexane or a methylaminomethylene moiety between the furan and diazoketo functions leads to the formation of a hydroindenone and pyrrolone, respectively. Replacement of the diazomethylketo terminus by an α-diazoethylketo system or a α-diazo-β-keto-ester function produces 2-substituted 2-cycloalkenones. A furan with a C₄, diazo-methylketo-terminating side-chain at C(3) is described to be transformed into a 4-formylmethylidene-2-cyclohe-xenone.     

Fluorescence depolarization and contact angle investigation of dynamic and static interfacial tension of liquid crystal display materials

Interfacial interactions control two processes empirically known to be critical for molecular anchoring in twisted nematic liquid crystal displays technology (TN-LCDs): surface treatment and filling procedure. Static and dynamical interfacial tensions (Gamma(SL)) between liquids and several substrates with similar roughness were observed respectively by contact angle (theta(c)) of sessile drops and by fluorescence depolarization of thin liquid films flowing at high velocity. Gamma(SL) decreased when glass was coated with tin dioxide and increased with polyvinyl alcohol (PVA) deposition. Drops were circular for all substrates except rubbed PVA, where they flowed spontaneously along the rubbing direction, reaching an oblong form that had theta(c) parallel and perpendicular to the rubbing direction respectively greater and smaller than theta(c) for non-rubbed PVA. This is attributed to polar group alignment generating an asymmetric Gamma(SL) distribution with nanometric preferential direction, inducing a capillary-like flow. Polarization and anisotropy maps for high-velocity flow parallel to the PVA rubbing direction showed an increase in the net alignment of molecular domains and a widening of the region where it occurred. This is attributed to preferential anchoring in the downstream direction, instead of in several directions, as for non-rubbed PVA. This explains why filling direction is crucial for TN-LCDs homogeneous behavior.     

An Infrared-Finite Algorithm for Rayleigh Scattering Amplitudes,and Bohr's Frequency Condition

In this paper, we rigorously justify Bohr’s frequency condition in atomic spectroscopy. Moreover, we construct an algorithm enabling us to calculate the transition amplitudes for Rayleigh scattering of light at an atom, up to a remainder term of arbitrarily high order in the finestructure constant. Our algorithm is constructive and circumvents the infrared divergences that invalidate standard perturbation theory.     

Synthetic magnetic opals

We present studies of novel nanocomposites of BiNi impregnated into the structure of opals as well as inverse opals. Atomic force microscopy and high resolution elemental analyses show a highly ordered structure and uniform distribution of the BiNi filler in the matrix. These BiNi-based nanocomposites are found to exhibit distinct ferromagnetic-like ordering with transition temperature of about 675 K. As far as we know there exists no report in literature on any BiNi compound which is magnetic.     

Self-focussing of a laser beam in a multiply ionized,absorbing plasma

Using a numerical code we have studied self-focussing of an intense laser beam which is propagating through a multiply-ionized absorbing plasma. The effecient self-focussing threshold has been calculated as a function of various pulse and plasma parameters.