First-principle study of nanostructures of functionalized graphene

We present first-principle calculations of 2D nanostructures of graphene functionalized with hydrogen and fluorine, respectively, in chair conformation. The partial density of states, band structure, binding energy and transverse displacement of C atoms due to functionalization (buckling) have been calculated within the framework of density functional theory as implemented in the SIESTA code. The variation in band gap and binding energy per add atom have been plotted against the number of add atoms, as the number of add atoms are incremented one by one. In all, 37 nanostructures with 18C atoms, 3 × 3 × 1 (i.e., the unit cell is repeated three times along x-axis and three times along y-axis) supercell, have been studied. The variation in C–C, C–H and C–F bond lengths and transverse displacement of C atoms (due to increase in add atoms) have been tabulated. A large amount of buckling is observed in the carbon lattice, 0.0053–0.7487 Å, due to hydrogenation and 0.0002–0.5379 Å, due to fluorination. As the number of add atoms (hydrogen or fluorine) is increased, a variation in the band gap is observed around the Fermi energy, resulting in change in behaviour of nanostructure from conductor to semiconductor/insulator. The binding energy per add atom increases with the increase in the number of add atoms. The nanostructures with 18C+18H and 18C+18F have maximum band gap of 4.98 eV and 3.64 eV, respectively, and binding energy per add atom –3.7562 eV and –3.3507 eV, respectively. Thus, these nanostructures are stable and are wide band-gap semiconductors, whereas the nanostructures with 18C+2H, 18C+4H, 18C+4F, 18C+8F, 18C+10F and 18C+10H atoms are small band-gap semiconductors with the band gap lying between 0.14 eV and 1.72 eV. Fluorine being more electronegative than hydrogen, the impact of electronegativity on band gap, binding energy and bond length is visible. It is also clear that it is possible to tune the electronic properties of functionalized graphene, which makes it a suitable material in microelectronics.     

Infrared differential absorption lidar for stand-off detection of chemical agents

A compact trolley-mounted pulsed transverse electric atmospheric pressure (TEA) carbon dioxide laser-based differential absorption lidar (DIAL) system capable of stand-off detection of chemical clouds in aerosol and vapour form upto about 200 m range in the atmosphere has been developed and assembled at Laser Science and Technology Centre (LASTEC), Delhi. The system was tested successfully with diethyl ether (DEE) (a toxic industrial chemical (TIC)) and differential absorption signals at $\lambda _{\text {on}}$ (strong absorption, 9R16) and $\lambda _{\text {off}}$ (weak absorption, 10R26) wavelengths were recorded for stand-off distances upto $\sim $ 100 m (open air ground path). This paper discusses the technical details of trolley-mounted CO₂ DIAL system and the data generated during the test and evaluation of this sensor using DEE aerosols.     

Oxidation of crotyl alcohol by N-chloro-4-methylbenzene sulphonamide in acidic medium and in alkaline media in the presence of os(VIII) catalyst-a kinetic pathway

The kinetic pathway of oxidation of crotyl alcohol by sodium salt of N -chloro-4-methylbenzene sulphonamide (chloramine-T) in acidic and alkaline medium has been studied. The speciation of chloramine-T has been made to suggest a proper and reasonable reaction mechanism. The thermodynamic quantities such as activation energy and activation entropy are evaluated in acidic as well as in catalysed alkaline medium. An anticipated reaction mechanism has been suggested.     

Thermal birefringence-compensated linear intracavity frequency doubled Nd:YAG rod laser with 73 ns pulse duration and 160 W green output power

In a thermally birefringence-compensated linear cavity configuration, ～160 W of average green power by intracavity frequency doubling of AO Q-switched Nd:YAG/LBO-based laser is demonstrated. The corresponding optical to optical conversion efficiency is estimated to be ～ 12.7%. The pulse repetition rate is 20 kHz with the individual pulse duration of 73 ns. The beam quality parameter is measured to be 18.     

Theoretical Evaluation of the Global and Local Electrophilicity Patterns to Characterize Hetero Diels-Alder Cycloaddition in the Synthesis of Isoxazolo[4,5-e](1,2,3,4-tetrazine)

A series of substituted dienophiles 1—10 and three 1,2-diazadienes namely D-1, D-2, D-3 were chosen to understand the reactivity and selectivity of Diels-Alder cycloaddition. The global and local electrophilicity patterns have been evaluated on a series of cycloaddition reactions to assess the reaction pathways (NDAC/IEDDAC) using the absolute scale of electrophilicity proposed by Parr et al. Regional electrophilicity at the active sites of the reagents involved in Diels-Alder processes has been described on a quantitative basis using local or regional electrophilicity index i.e. Fukui function. Good qualitative/quantitative comparison was found between molecular energy gaps and global electronic parameters, which has been employed to assess the cycloaddition pathways successfully.     

Role of Ge incorporation in the physical and dielectric properties of Se<Subscript>75</Subscript>Te<Subscript>25</Subscript> and Se<Subscript>85</Subscript>Te<Subscript>15</Subscript> glassy alloys

The effect of Ge additive on the physical and dielectric properties of Se₇₅Te₂₅ and Se₈₅Te₁₅ glassy alloys has been investigated. It is inferred that on adding Ge, the physical properties i.e., average coordination number, average number of constraints and average heat of atomization increase but lone pair electrons, fraction of floppy modes, electronegativity, degree of crosslinking and deviation of stoichiometry (R) decrease. The effect of Ge doping on the dielectric properties of the bulk Se₇₅Te₂₅ and Se₈₅Te₁₅ glassy alloys has also been studied in the temperature range 300–350 K for different frequencies (1 kHz–5 MHz). It is found that, with doping, the dielectric constant ε^′ and dielectric loss ε^″ increase with increase in temperature and decrease with increase in frequency. The role of the third element Ge, as an impurity in the two pure binary Se₇₅Te₂₅ and Se₈₅Te₁₅ glassy alloys has been discussed in terms of the nature of covalent bonding and electronegativity difference between the elements used in making the aforesaid glassy systems.     

Silica‐gel‐supported Phosphorus Pentoxide:a Simple and Efficient Solid‐supported Reagent for Esterification of Long‐ Chain Carboxylic Acids and Their Antimicrobial Screening

A silica-gel-supported heterogeneous phosphorus pentoxide reagent has been developed for the esterification of various long-chain carboxylic acids with aromatic alcohols. The reactions occurred under relatively mild conditions and afforded the desired products in good yields. All the compounds 3a—3x were screened for antibacterial and antifungal activity, which showed good activity against Gram positive and Gram negative bacteria and also good results against almost all fungal strains. The structures of the synthesized compounds were elucidated by IR, ¹H NMR, ¹³C NMR, mass spectroscopic techniques and elemental analysis.     

Femto-Second Transform Limited Pulse Generation with Higher Order Dispersion Effects for Dispersion-Shifted Optical Communication System

The paper deals with the influence of higher-order effects of dispersion on the femto-second transform limited pulse generation by compensating for linear chirp of self-phase modulation spectra in the dispersion-shifted fibers. It has been shown that the minimum propagation length with first-order dispersion term is 23 m, as reported earlier. If the higher-order dispersion effects are taken into consideration, this length is reduced to 11.5 m. With compensation of the first-order dispersion term, this length can be enhanced to 6.8161 × 10³ km. This length can further be improved to 6.0343 × 10⁹ km by compensation of first- and second-order dispersion terms together. The minimum pulse width and linewidth product without dispersion, with dispersion including higher-order dispersion effects, and with dispersion compensation, is found to be 0.44, 0.4418, and 0.4411, respectively.