Single fractional monolayer (FM) CdSe/ZnSe structures have been grown by molecular beam epitaxy (MBE), employing both conventional MBE and migration-enhanced epitaxy (MEE). A precise calibration of the FM mean thickness in the range of 0.15–3.0 ML has been performed for both techniques, revealing more than a 3.5 times lower Cd incorporation ability for the MEE mode at the same Cd and Se incident fluxes. Steady-state and time-resolved photoluminescence spectroscopy is used to characterize the intrinsic morphology of the CdSe FMs, with a special emphasis on the submonolayer thickness range. Both MBE and MEE grown samples exhibit inhomogeneity of the excitonic system, which can be explained by coexistence of a homogeneous alloylike layer and relatively large CdSe 2D clusters. The MEE samples display smaller fluctuations of the layer thickness and island sizes.

Variability Search Toolkit (VaST) is a software package designed to find variable objects in a series of sky images. It can be run from a script or interactively using its graphical interface. VaST relies on source list matching as opposed to image subtraction. SExtractor is used to generate source lists and perform aperture or PSF-fitting photometry (with PSFEx). Variability indices that characterize scatter and smoothness of a lightcurve are computed for all objects. Candidate variables are identified as objects having high variability index values compared to other objects of similar brightness. The two distinguishing features of VaST are its ability to perform accurate aperture photometry of images obtained with non-linear detectors and handle complex image distortions. The software has been successfully applied to images obtained with telescopes ranging from 0.08 to 2.5 m in diameter equipped with a variety of detectors including CCD, CMOS, MIC and photographic plates. About 1800 variable stars have been discovered with VaST. It is used as a transient detection engine in the New Milky Way (NMW) nova patrol. The code is written in C and can be easily compiled on the majority of UNIX-like systems. VaST is free software available at http://scan.sai.msu.ru/vast/

The weak-field dielectric dispersion ͑100 Hz-1.8 GHz͒ studies both of pure and Fe 2ϩ /Fe 3 modified Cd 2 Nb 2 O 7 ceramics over the temperature range of 90-380 K are presented and discussed from the viewpoint of relaxor and glassy properties of the system. It is revealed that In the latter, at T C ϭ196 K the dielectric relaxation due to the motion of ferroelectric domain walls driven by an external ac electric field is observed. A polydispersive dielectric response of Cd 2 Nb 2 O 7 around 188 K has characteristics of the relaxor ferroelectrics with glassy behavior ͑like PMN͒. Near the characteristic freezing temperature of the zero-field-cooled state (T f ϭ183 K) the dielectric absorption spectra and the relaxation-time distribution strongly broaden and tend to flatten out, while below T f the imaginary part of the dielectric permittivity becomes nearly frequency independent. The dielectric response of Cd 2 Nb 2 O 7 dominating far below T C ͑around 150 K͒ and that of Fe 2ϩ /Fe 3ϩ doped CdNb 2 O 6 between 90 and 380 K are typical of glass-forming systems at temperature far above T glass . The relaxational process is characterized by ͑i͒ a significant frequency dependence of the peak permittivity position, ͑ii͒ non-Arrhenius behavior, and ͑iii͒ increasing asymmetry of the dielectric absorption spectrum at the low-frequency side with decreasing temperature, without broadening the relaxation-time distribution and freezing the peak-absorption frequency. It is proposed that although the nature of structural disorder in Cd 2 Nb 2 O 7 pyrochlore and Fe 2ϩ /Fe 3ϩ doped CdNb 2 O 6 columbite is different, in both systems the off-center displacements of the A-site ions act as a random field and are responsible for the relaxor and dipolar glass-like behavior upon cooling. The Debye-like HF dielectric relaxation ͑1 MHz-1.8 GHz͒ observed both in Cd 2 Nb 2 O 7 and its isostructural analog Cd 2 Ta 2 O 7 at RT and higher ͑a centrosymmetric phase͒ is attributed to fluctuations in polarization of the dynamically reoriented O͑7th͒-Cd-O͑7th͒ dipoles due to dynamical off-center location of Cd ions.

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