High-quality ZnS shells for CdSe nanoparticles: rapid microwave synthesis

Using a domestic microwave oven and new, inexpensive precursors, a rapid and reliable synthesis of highly luminescent CdSe/ZnS NPs was developed. To evaluate the quality of our core/shell particles for varying shell thickness in comparison to that of CdSe/ZnS nanoparticles obtained commercially, the parameter fluorescence quantum yield is been used as well as a new, straightforward, thiophenol-based shell-quality test as a tool to ensure a dense ZnS shell without holes and cracks, which is a prerequisite for high luminescence and stability.     

Subsecond spin relaxation times in quantum dots at zero applied magnetic field due to a strong electron-nuclear interaction

A key to ultralong electron spin memory in quantum dots (QDs) at zero magnetic field is the polarization of the nuclei, such that the electron spin is stabilized along the average nuclear magnetic field. We demonstrate that spin-polarized electrons in n-doped (In,Ga)As/GaAs QDs align the nuclear field via the hyperfine interaction. A feedback onto the electrons occurs, leading to stabilization of their polarization due to formation of a nuclear spin polaron [I. A. Merkulov, Phys. Solid State 40, 930 (1998)]. Spin depolarization of both systems is consequently greatly reduced, and spin memory of the coupled electron-nuclear spin system is retained over 0.3 sec at temperature of 2 K.     

Autocatalytic Green Synthesis of Imines in Traceless Medium

For the first time, condensations of amines with carbonyl compounds have been performed in supercritical carbon dioxide (sc-CO₂). The reactions with aldehydes or active ketones proceed at moderate temperatures (35–55 °C) without use of external catalysts. The process is autocatalytic: it is accelerated by the carbonic acid generated in situ by interaction between the released water and the CO₂ medium. The imine products were obtained in high yields in a crystalline form and did not require further purification. The one-pot transfer hydrogenation and [4+2] cycloaddition reactions performed in the CO₂ medium have uncovered attractive prospects for facile green synthesis of more complex and valuable compounds from the generated in situ imine products.     

The Extended Moduli Space of¶Special Lagrangian Submanifolds

It is well known that the moduli space of all deformations of a compact special Lagrangian submanifold X in a Calabi–Yau manifold Y within the class of special Lagrangian submanifolds is isomorphic to the first de Rham cohomology group of X. Reinterpreting the embedding data X⊂Y within the mathematical framework of the Batalin–Vilkovisky quantization, we find a natural deformation problem which extends the above moduli space to the full de Rham cohomology group of X. Received: 29 June 1998 / Accepted: 7 June 1999     

Size quantization of acoustic phonons in CuCl nanocrystals

It is shown that the mixed character of spheroidal vibrational modes of semiconductor quantum dots of spherical shape may lead to the appearance of a line in the low-frequency Raman spectra of nanocrystals whose spec-tral position is independent of the average radius of nanocrystals in the sample over a wide range of sizes. This effect is associated with the rapid saturation of the dispersion dependence for transversal acoustic phonons in the bulk semiconductor. The maximum radius of quantum dots at which the line indicated above is observed in the spectrum has been estimated.     

Deformation Quantization of the n-tuple Point

Contrary to the classical methods of quantum mechanics, the deformation quantization can be carried out on phase spaces which are not even topological manifolds. In particular, the Moyal star product gives rise to a canonical functor F from the category of affine analytic spaces to the category of associative (in general, non-commutative) ℂ-algebras. Curiously, if X is the n-tuple point, x ⁿ =0, then F(X) is the algebra of n×n matrices. Received: 4 November 1998 / Accepted: 3 March 1999     

On possible conical singularities in magneto-optics

The conditions for the appearance of conical singularities in a magnetically ordered crystal in the presence of dichroism, birefringence, and magneto-optical activity have been considered. The possibility of the existence of singularities such as a nodal point, cusp, and point of contact has been demonstrated. The relation of the topological index of the closed singular line to the indices of the C points lying inside the contour has been revealed. Estimates have been made for the YIG:Bi crystal.     

Formality Theorem for Quantizations of Lie Bialgebras

Using the theory of props we prove a formality theorem associated with universal quantizations of Lie bialgebras.     

Possibilities of NMR spectrometry in determining trace components of mixtures

The possibility of using nuclear magnetic resonance (NMR) spectrometry for the determination of trace components in mixtures in the concentration range 1 × 10^?5–5 × 10^?4 M is shown. The conditions of NMR experiments at which the measurement error attains a minimum are standardized and the precision of NMR spectrometry in determining trace components of mixtures within the analytical range is estimated.     

Effect of a mudcake on the propagation of stoneley waves in a borehole

The problem of detecting a permeable stratum blocked by a mudcake with the help of acoustic measurements inside a borehole is considered. Different physical models of the mudcake are compared: in the form of a highly viscous liquid layer, in the form of a soft elastic shell, and in the form of an elastic shell fixed in an arbitrary way to the borehole walls. Numerical calculations are presented for the wave field in a borehole.