Densitometric HPTLC Method for Analysis of Oleanolic Acid in Achyranthes aspera L.

JPC – Journal of Planar Chromatography – Modern TLC - Adensitometric HPTLC method has been established for analysis in alcohol extracts of the seeds and leaves of Achyranthes aspera L....     

Implementation of anti-reflection coating to enhance light out-coupling in organic light-emitting devices

We report significant enhancement of light out-coupling in organic light-emitting devices (OLEDs) by means of anti-reflection coating of magnesium fluoride (MgF₂) on the backside of glass substrate. OLEDs were fabricated by employing the green electrophosphorescent material fac tris-(2-phenylpyridine) iridium [Ir(ppy)₃] doped in 4,4′,8-N,N-8-dicarbazole-biphenyl (CBP) and 0.4 wt% tetrafluorotetracyano-quinodimethane (F4-TCNQ)-doped naphthylphenylbiphenyl diamine (α-NPD) as hole transport layer (HTL). Single-layer MgF₂ with the thickness of λ/4 was then vacuum deposited on the backside of glass substrate of OLED. About two-fold enhancement in luminance with anti-reflection coating of MgF₂ has been observed.     

Multipoint parallel excitation and CCD-based imaging system for high-throughput fluorescence detection of biochip micro-arrays

We report the development and the characterization of a multipoint parallel excitation and CCD-based imaging system for high-throughput fluorescence detection of biochip micro-arrays. A two-dimensional array of (19×19) points with uniform intensity distribution, generated by a holographic array generator, was used for parallel excitation of two-dimensional micro-arrays of fluorescence samples. A CCD-based imaging system was used for high-throughput parallel detection and quantitative analysis of the fluorescence output. Micro-array samples of cyanine (Cy5) dye dots on silicon wafers and on glass substrates with varying concentration were used to evaluate the performance of the system. Results of fluorescence intensity measurements with varying concentration of dye and with different image acquisition time are presented. We have demonstrated that this novel approach will, in general, outperform the conventional approach in the excitation efficiency, the signal-to-noise ratio, and the throughput. The limitations and the potential improvements of the present method are discussed.     

Observation of compensation effect for isothermal crystallization in glassy Se80?xGe20Inx and Se78?xGe22Bix alloys

Many activated phenomena, including solid state diffusion in crystals and polymers, dielectric relaxation, conduction and thermally stimulated processes in polymers, and electronic conduction in amorphous semiconductors obey the compensation law or Meyer-Neldel rule. In the present paper, we discuss the results of investigation into the compensation effect observed under isothermal crystallization in glassy Se₇₀Te_30−xSb_x alloys. It is found that the relation between the pre-exponential factor K_o and activation energy of crystallization E_c follows the Meyer-Neldel rule for the alloys studied. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 45–51, March, 2008.     

Near-field turbulence properties of single- and two-stream plane mixing layers

Detailed mean flow and turbulence measurements have been made in the near-field of two plane mixing layers in air with a maximum velocity of 21 m/s. The experimental rig enabled mixing layers of velocity ratios 0 and 0.46 to be generated simultaneously. Cases with both tripped and untripped initial boundary layers were studied. In all cases, it was found that the two-stream layer developed to the self-preserving state in a distance much shorter than the single-stream layer, which followed accepted criteria for the development distance. The asymptotic levels of the turbulence quantities in the two-stream layer and the development of the single-stream layer showed agreement with existing data. The results suggest that the two-stream mixing layer should provide a better test case for the development of turbulence models and calculation methods than the single-stream mixing layer.     

Proton-nucleus optical model potential at low energies—a review

Ever since it was proposed more than three decades ago, the nuclear optical model has been very successful in interpreting a large body of nucleon-induced nuclear reaction data in terms of a complex nucleon-nucleus potential. Rapid progress both in the experimental measurements and the theoretical developments in the last two decades has led to a better understanding of this nucleon-nucleus optical potential. From the parameter-fitting phenomenological stage, the optical model has come a long way and it is now possible to calculate the nucleon-nucleus optical potential in a reasonable way starting from the fundamental nucleon-nucleon interaction. Excellent reviews on various aspects of the optical model exist in the literature for proton energies above 10 MeV. The present article is an attempt to review comprehensively the status of the proton-nucleus optical potential at low proton energies, below the Coulomb-barrier, for target nuclei with mass numbers lying between 40 and 130. The sets of phenomenological optical potential derived mostly from (p, n) reaction data are reviewed and their applicabilities discussed. The neutron-nucleus optical model is referred to wherever it is relevant. Microscopic calculations for one case is carried out and compared with the corresponding phenomenological values.     

Effects of small changes in initial conditions on mixing layer three-dimensionality

Conclusions An experimental study which shows the effects of relatively small changes in the initial conditions on the development of the three-dimensional structure of a plane mixing layer originating from laminar boundary layers has been completed. It was shown that while the exact shapes and positions of the streamwise vortex structures are not the same for the two initial conditions, their overall distribution, reorganization and decay are very similar. The present results imply that while some of the specific details of the streamwise vortex structure may be facility dependent, a relatively strong structure, which produces significant three-dimensionality, should form in all mixing layers originating from laminar boundary layers. After some initial readjustments, the structure will appear in the form of counter-rotating pairs of streamwise vortices which, in the mean, grow with the mixing layer and decay in strength.The present results also serve as a warning that small changes in initial conditions may significantly affect the Reynolds stress distributions in the near-field. The most likely mechanism for this is through the effects of very small changes in initial boundary layer properties on the details (strength and location) of the spanwise vortex roll-up. Despite these relatively large differences in the near-field, both mixing layers attain comparable turbulence structure and growth rates in the far-field. In addition, the behavior of the streamwise vortex structure does not appear to be affected by the differences in the near-field Reynolds stress distributions.     

Validated HPTLC Method for Assay of Prednisolone in Tablets and Comparison with Pharmacopeial Methods

JPC – Journal of Planar Chromatography – Modern TLC - A rapid and reliable high-performance thin-layer chromatographic method has been established for analysis of prednisolone in a...     

A one-flask synthesis and characterization of novel symmetrical pyridyl monoselenides and X-ray crystal structure of bis(5-bromo-2-pyridyl) selenide and bis(2-bromo-5-pyridyl) selenide

The present work reports an efficient one-pot synthesis of symmetrical pyridyl monoselenides by the reaction of bromo-/iodopyridines with the isopropylmagnesium chloride, ⁱPrMgCl followed by quenching with selenyl chloride, SeCl₂. The current methodology constitutes a convenient synthesis of bis(5-bromo-2-pyridyl) selenide (I), bis(2-bromo-5-pyridyl) selenide (II) and bis(2,5-dibromo-3-pyridyl) selenide (III) under cryogenic conditions requiring shorter time duration to give satisfactory yields. The hitherto unknown compounds have been characterized by elemental analysis and various spectroscopic techniques i.e., ¹H NMR, ¹³C NMR, FT-IR, mass spectrometry and X-ray crystallography.     

A vicarious one-pot transformation of a fluorocyclitol to a polycyclitol: observation of a formal 4-fold axial-equatorial epimerization on a conformationally locked scaffold

A conformationally locked fluoropentol undergoes an interesting transformation to (trans,anti,trans,anti,trans)-perhydro-2,3,4a,6,7,8a-naphthalenehexol essentially under conditions of base-induced transesterification. The proposed rationale for the observed metamorphosis involves a nucleophilic displacement of fluoride, and subsequent stereo- and regioselective anti-Fürst-Plattner-type ring-opening of the epoxide thus formed.