Origin of ultrafast excited state dynamics of 1-nitropyrene

Time-resolved emission measurements in subpicosecond time domain have been carried out for 1-nitropyrene in different solvents to understand the mechanism for the observed ultrafast decay of its first excited singlet state. Excited-state dynamics of 1-nitropyrene is found to be independent of the solvent viscosity. This result contradicts the proposition in the literature (J. Phys. Chem. A 2007, 111, 552) that the ultrafast decay in 1-nitropyrene is due to the large amplitude torsional motion of the nitro group around the pyrene moiety. Excited-state dynamics of 1-nitropyrene in solvents with different dielectric constants shows that excited-state lifetime suddenly increases after a certain value of the dielectric constant. Detailed quantum chemical calculations have been carried out to understand the process that is responsible for the observed effect of the dielectric constant on the excited-state dynamics of 1-nitropyrene. It is seen that the excited-state lifetime and the singlet-triplet energy gap follow similar variation with the dielectric constant of the medium. Such a correlation between the excited-state lifetime and the singlet-triplet energy gap supports the fact that the observed ultrafast decay for 1-nitropyrene is due to an efficient intersystem crossing rather than to the torsional motion of the nitro group as proposed in the literature.     

A nano-confined charged layer defies the principle of electrostatic interaction

The reactivity between two charged molecules and the activity of charged biomolecules are mainly governed by the principle of electrostatic interaction, i.e., like charges repel and opposite charges attract. In the present study it is shown that the principle of electrostatic interaction is violated in the nano-confined biomimetic environment. Thus a positively charged molecule shows more preference to a positively charged surface compared to a negatively charged surface.     

Magnetoelectric response and dielectric property of multiferroic Co0.65Zn0.35Fe2O4–PbZr0.52Ti0.48O3 nanocomposites

The effect of nanometric grain size modulation on the behavior of different kinds of chemically synthesized multiferroic ferrite–ferroelectric nanocomposites with cobalt zinc ferrite (Co_0.65Zn_0.35Fe₂O₄) as a ferrimagnetic component and lead zirconate titanate (PbZr_0.52Ti_0.48O₃) as a ferroelectric component have been investigated in detail. Formation of two distinct pure phases of as-prepared nanocomposites was confirmed from recorded X-ray diffraction patterns at room temperature. The backscattered mode of a field emission scanning electron microscope micrograph has been used to study the microstructure, average grain size, and distribution of the two individual phases in the composites. Magnetization vs. magnetic field measurements clearly show the room temperature good hysteretic ferrimagnetic behavior of the composites having coercivity of 83–124 Oe and spontaneous magnetization of 20–24 emu/g. The dielectric constant is found to increase with increasing grain size of the nanocomposites from 124 to 687 at a frequency of 1 kHz. Investigation of temperature-dependent dielectric constant behavior reveals that the paraelectric–ferroelectric transition temperature decreases from 364 to 351 °C with decreasing particle size. A complex impedance spectroscopy study was carried out in the frequency range of 50 Hz–1 MHz and in the temperature range of 27–400 °C. The contribution of both grains and grain boundaries in the electrical properties of the composites has been confirmed from the complex impedance spectroscopy data. The activation energies estimated from the complex impedance spectroscopy and the ac conductivity spectrum are found to be nearly the same for the nanocomposites. The polarization vs. electric field measurement exhibits a typical ferroelectric hysteresis loop at room temperature and provides conclusive evidence of the presence of spontaneous polarization in the composites, confirming the presence of excellent ferroelectricity in the nanocomposites. At room temperature the multiferroic behavior of the composites is also confirmed from detailed magnetoelectric (ME) response studies. The optimal ME response is observed to be 0.6 % for higher temperature sintered composites.     

Effect of variation of dielectric constant on the magnetic field modulation of exciplex luminescence

The effect of variation of dielectric constant on the relative magnetic field effect in singlet luminescence has been studied using a typical exciplex system at a saturating field. The study indicates strong specificity in the perturbation of the magnetic field effect by alcoholic solvents. In contrast to alcohols where relative singlet magnetic field effect is of the order of 2% only, the magnetic field effect in non-alcoholic medium reaches as high as 9%. Moreover, dielectric constant variation in alcohols yields curves which are distinctly different from those in non-alcoholic media. It turns out that this dependence of magnetic field effect on dielectric constant is similar in all non-alcoholic solvent mixtures. An analytical study based on Hong and Noolandi’s solution of Smoluchowski equation has been made. Derived expressions can interpret experimental curves reasonably well.     

Efficient laser isotope separation of 13C using novel linear multi-pass cavity

¹³C isotope has been separated in the form of enriched product C₂F₄ by selective multi-photon dissociation (MPD) of Freon-22 (CHClF₂) using the 9P(26) laser line of a transversely excited atmospheric CO₂ laser. The non-linearity factor, γ, that determines the dependence of the yield of ¹³C isotope on the fluence (J/cm²) has been determined for various laser rotational lines (9P(20)–9P(26)) and the advantage of a lower γ in the case of 9P(26) is highlighted for macroscopic production of ¹³C isotope. It is also shown that a higher value of the optimum fluence at 9P(26) not only results in a higher enrichment efficiency but in a relatively lower value of γ also. The laser pulse energy is efficiently utilized for selective MPD of Freon-22 by focusing the pulse energy repeatedly with the help of a novel linear multi-pass cavity (LMPC). The novelty of this optical arrangement lies in its ability to maintain the laser fluence around an optimum value for a desired enrichment of ¹³C in the product. This also ensures a higher quantity of enriched product because of the higher reaction volume. The advantage of the LMPC over the conventionally used Herriott multi-pass cell has also been presented. The gain in reaction volume in the present optical cavity having 20 passes with a constant fluence in each pass is as high as 12. Isotope-selective MPD of Freon in a LMPC with constant fluence in each pass showed a distinct advantage in energy utilization to separate ¹³C isotope over the gradually reducing fluence case.This revised version was published online in August 2005 with a corrected cover date.     

Processing of concretes with a high power CO2 laser

Laser material processing, being a non-contact process, minimizes many of the complexities involved in the decontamination and decommissioning of nuclear facilities. A high power laser beam incident on a concrete surface can produce spalling, glazing or vaporization, depending upon the laser power density and scan speed. This paper presents effect of various laser processing parameters on the efficiency of material removal by surface spalling and glazing. The size of laser beam at constant fluence or energy density had significantly different effect on the spalling process. In thick concrete block cutting the flow or removal of molten material limits the cutting depth. By employing repeated laser glazing followed by mechanical scrubbing process cutting of 150 mm thick concrete block was carried out. Gravitation force was utilized for molten materials to flow out while drilling holes on vertical concrete walls. The dependence of the incident laser beam angle on drilling time was experimentally studied.     

Śrîpati: An eleventh-century Indian mathematician

?rîpati (fl. a.d. 1039–1056) is best known for his writings on astronomy, arithmetic, mensuration, and algebra. This article discusses ?rîpati's arithmetic, the Ga$\text{n}\text{?}$itatilaka, as well as the arithmetical and algebraic chapters of the Siddhânta?ekhara. In addition to discussing the kinds of problems considered by ?rîpati and the techniques he used to solve them, the article considers the sources upon which ?rîpati drew. A glossary of Indian treatises and technical terms is provided.     

On some properties of a linguistic classifier

A general structure of a linguistic classifier wherein sub-subclassifiers are the building blocks is suggested. Some properties of these sub-subclassifiers are proposed and proved. The physical significances of these properties are explored and it is shown that a condensed measure of belongingness of patterns to any class can be obtained which can conveniently be used for forming classification rules.     

On the effective computation of the inertia of a non-hermitian matrix

Summary given a complex lower Hessenberg matrixA with unit codiagonal, a hermitian matrixH is constructed such that, ifH is non-singular InA= InH. IfA is real,H is real symmetric. Classical results of Fujiwara on the root-separation problem and of Schwarz on the eigenvalue-separation problem are included as special cases.The authors' research was conducted at the Universidade Estadual de Campinas and supported by the Fundação de Amparo à Pesquisa do Estado de São Paulo, Brasil, under grant n⁰ 78/0490.