27,744 research outputs found
Quenching of fluorescence of aromatic molecules by graphene due to electron transfer
Investigations on the fluorescence quenching of graphene have been carried
out with two organic donor molecules, pyrene butanaoic acid succinimidyl ester
(PyBS, I) and oligo(p-phenylenevinylene) methyl ester (OPV-ester, II).
Absorption and photoluminescence spectra of I and II recorded in mixture with
increasing the concentrations of graphene showed no change in the former, but
remarkable quenching of fluorescence. The property of graphene to quench
fluorescence of these aromatic molecules is shown to be associated with
photo-induced electron transfer, on the basis of fluorescence decay and
time-resolved transient absorption spectroscopic measurements.Comment: 18 pages, 6 figure
Charge order suppression and antiferromagnetic to ferromagnetic switch over in Pr_0.5Ca_0.5MnO_3 nanowires
We have prepared crystalline nanowires (diameter ~ 50 nm, length ~ a few
microns) of the charge ordering manganite Pr_0.5Ca_0.5Mn_O3 using a low
reaction temperature hydrothermal method and characterized them using X-ray
diffraction, transmission electron microscopy, SQUID magnetometry and electron
magnetic resonance measurements. While the bulk sample shows a charge ordering
transition at 245 K and an antiferromagnetic transition at 175 K, SQUID
magnetometry and electron magnetic resonance experiments reveal that in the
nanowires phase, a ferromagnetic transition occurs at ~ 105 K. Further, the
antiferromagnetic transition disappears and the charge ordering transition is
suppressed. This result is particularly significant since the charge order in
Pr_0.5Ca_0.5MnO_3 is known to be very robust, magnetic fields as high as 27 T
being needed to melt it.Comment: 12 pages including 4 figures. submitted to Applied Physics Letter
Low radio frequency signatures of ram pressure stripping in Virgo spiral NGC 4254
We report the detection of extended low radio frequency continuum emission
beyond the optical disk of the spiral galaxy NGC 4254 using the Giant Metrewave
Radio Telescope. NGC 4254, which has an almost face-on orientation, is located
in the outskirts of the Virgo cluster. Since such extended emission is uncommon
in low inclination galaxies, we believe it is a signature of magnetised plasma
pushed out of the disk by ram pressure of the intracluster medium as NGC 4254
falls into the Virgo cluster. The detailed spectral index distribution across
NGC 4254 shows that the steepest spectrum alpha < -1 (S propto nu^{alpha})
arises in the gas beyond the optical disk. This lends support to the ram
pressure scenario by indicating that the extended emission is not from the disk
gas but from matter which has been stripped by ram pressure. The steeper
spectrum of the extended emission is reminiscent of haloes in edge-on galaxies.
The sharp fall in intensity and enhanced polarization in the south of the
galaxy, in addition to enhanced star formation reported by others provide
evidence towards the efficacy of ram pressure on this galaxy. HI 21cm
observations show that the gas in the north lags in rotation and hence is
likely the atomic gas which is carried along with the wind. NGC 4254 is a
particularly strong radio emitter with a power of 7x10^{22} Watts/Hz at 240
MHz. We find that the integrated spectrum of the galaxy flattens at lower
frequencies and is well explained by an injection spectrum with
alpha_0=-0.45+-0.12. We end by comparing published simulation results with our
data and conclude that ram pressure stripping is likely to be a significant
contributor to evolution of galaxies residing in X-ray poor groups and cluster
outskirts.Comment: 10 pages, 7 figures (figures 1,2 and 4 are in jpg format) and 2
tables; Accepted for publication in MNRA
Novel magnetic properties of graphene: Presence of both ferromagnetic and antiferromagnetic features and other aspects
Investigations of the magnetic properties of graphenes prepared by different
methods reveal that dominant ferromagnetic interactions coexist along with
antiferromagnetic interactions in all the samples. Thus, all the graphene
samples exhibit room-temperature magnetic hysteresis. The magnetic properties
depend on the number of layers and the sample area, small values of both
favoring larger magnetization. Molecular charge-transfer affects the magnetic
properties of graphene, interaction with a donor molecule such as
tetrathiafulvalene having greater effect than an electron-withdrawing molecule
such as tetracyanoethyleneComment: 16 pges, 5 figure
Femtosecond carrier dynamics and saturable absorption in graphene suspensions
Nonlinear optical properties and carrier relaxation dynamics in graphene,
suspended in three different solvents, are investigated using femtosecond (80
fs pulses) Z-scan and degenerate pumpprobe spectroscopy at 790 nm. The results
demonstrate saturable absorption property of graphene with a nonlinear
absorption coefficient, , of ~2 to 9x10^-8 cm/W. Two distinct time scales
associated with the relaxation of photoexcited carriers, a fast one in the
range of 130-330 fs (related to carrier-carrier scattering) followed by a
slower one in 3.5-4.9 ps range (associated with carrier-phonon scattering) are
observed.Comment: 3 pages, 2 figures, 2 table
The performance of modified jatropha-based nanofluid during turning process
The industry's extensive use of petroleum-based metalworking fluid (MWF) harms the environment
and humans. The production of bio-based MWF, especially from crude jatropha oil (CJO), has therefore taken
numerous initiatives. This aimed to formulate newly modified jatropha oil (MJO) with the addition of 0.05wt.%
hBN and 0.05wt.% MoS2 as the nanofluid for MWF. The performance of the nanofluids was determined
through the turning process in terms of cutting temperature, workpiece surface roughness, tool life and tool
wear of the tool lubricated by the nanofluids. The performance of the nanofluid samples was compared with
the synthetic ester (SE). From the results, after conducted 100mm axial cutting length MJO+hBN+MoS2
recorded the lowest in cutting temperature and surface roughness compared to all samples. The result shows
that MJO+hBN+MoS2 has longer tool life (6500mm) compared to SE (6000mm). Abrasion and adhesion were
observed as the dominant tool wear mechanism. In conclusion, MJO+hBN+MoS2 shows better machining
performance and has the potential to be an environmentally friendly metalworking fluid
Multi component one pot synthesis and characterization of derivatives of 2-amino-7,7- dimethyl-5-oxo-4-phenyl-5,6,7,8-tetrahydro-4H-chromene-3-carbonitrile and study of anti-microbial activity
An efficient and convenient procedure has been described for one-pot multi-component synthesisof tetrahydrobenzo[b]pyrans known as 2-amino-7,7-dimethyl-5-oxo-4-phenyl-5,6,7,8-tetrahydro-4H-chromene-3-carbonitrile which can be obtained from the reaction of substituted aromatic aldehydes, dimedone, malonitrile, in the presence of base such as potassium tertiary butoxide and THF in methanol as solvent at RT condition. All the compounds were examined by advanced spectroscopic data (1H NMR, 13C NMR and LCMS) and the structural determination was evaluated by elemental analysis. In addition to this, all the newly synthesized compounds were examined for their antibacterial activities and antifungal activity by disc diffusion method against the organism of Aspergillus niger and Candida ablicans L. KEY WORDS: Aromatic aldehydes, Dimedone, Malonitrile, Potasium tertiary butoxide, 2-Amino-7,7-dimethyl-5-oxo-4-phenyl-5,6,7,8-tetrahydro-4H-chromene-3-carbonitrile, Anti-microbial activity Bull. Chem. Soc. Ethiop. 2018, 32(1), 133-138DOI: https://dx.doi.org/10.4314/bcse.v32i1.1
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