Femtosecond Photoexcited Carrier Dynamics in Reduced Graphene Oxide Suspensions and Films

We report ultrafast response of femtosecond photoexcited carriers in single layer reduced graphene oxide flakes suspended in water as well as few layer thick film deposited on indium tin oxide coated glass plate using pump-probe differential transmission spectroscopy at 790 nm. The carrier relaxation dynamics has three components: ~200 fs, 1 to 2 ps, and ~25 ps, all of them independent of pump fluence. It is seen that the second component (1 to 2 ps) assigned to the lifetime of hot optical phonons is larger for graphene in suspensions whereas other two time constants are the same for both the suspension and the film. The value of third order nonlinear susceptibility estimated from the pump-probe experiments is compared with that obtained from the open aperture Z-scan results for the suspension.Comment: 4 pages, 4 figures, to appear in International Journal of Nanoscience (IJN), 201

Ultrafast switching time and third order nonlinear coefficients of microwave treated single walled carbon nanotube suspensions

Microwave treated water soluble and amide functionalized single walled carbon nanotubes have been investigated using femtosecond degenerate pump-probe and nonlinear transmission experiments. The time resolved differential transmission using 75 femtosecond pulse with the central wavelength of 790 nm shows a bi-exponential ultrafast photo-bleaching with time constants of of 160 fs (130 fs) and 920 fs (300 fs) for water soluble (amide functionalized) nanotubes. Open and closed aperture z-scans show saturation absorption and positive (negative) nonlinear refraction for water soluble (amide functionalized) nanotubes. Two photon absorption coefficient,beata ~250 cm/GW (650 cm/GW) and nonlinear index, gamma ~ 15 cm^2/pW (-30 cm^2/pW) are obtained from the theoretical fit in the saturation limit to the data for two types of nanotubes.Comment: 15 pages, 4 figure

Large-amplitude chirped coherent phonons in tellurium mediated by ultrafast photoexcited carrier diffusion

We report femtosecond time-resolved reflectivity measurements of coherent phonons in tellurium performed over a wide range of temperatures (3K to 296K) and pump laser intensities. A totally symmetric A$_{1}$ coherent phonon at 3.6 THz responsible for the oscillations in the reflectivity data is observed to be strongly positively chirped (i.e, phonon time period decreases at longer pump-probe delay times) with increasing photoexcited carrier density, more so at lower temperatures. We show for the first time that the temperature dependence of the coherent phonon frequency is anomalous (i.e, increasing with increasing temperature) at high photoexcited carrier density due to electron-phonon interaction. At the highest photoexcited carrier density of $\sim$ 1.4 $\times$ 10$^{21}$cm$^{-3}$ and the sample temperature of 3K, the lattice displacement of the coherent phonon mode is estimated to be as high as $\sim$ 0.24 \AA. Numerical simulations based on coupled effects of optical absorption and carrier diffusion reveal that the diffusion of carriers dominates the non-oscillatory electronic part of the time-resolved reflectivity. Finally, using the pump-probe experiments at low carrier density of 6 $\times$ 10$^{18}$ cm$^{-3}$, we separate the phonon anharmonicity to obtain the electron-phonon coupling contribution to the phonon frequency and linewidth.Comment: 22 pages, 6 figures, submitted to PR

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, $beta$, 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

Large nonlinear absorption and refraction coefficients of carbon nanotubes estimated from femtosecond Z-scan measurements

Nonlinear transmission of 80 and 140 femtosecond pulsed light with $0.79 \mu m$ wavelength through single walled carbon nanotubes suspended in water containing sodium dodecyl sulphate is studied. Pulse-width independent saturation absorption and negative cubic nonlinearity are observed, respectively, in open and closed aperture Z-scan experiments. The theoretical expressions derived to analyze the z-dependent transmission in the saturable limit require two photon absorption coefficient $\beta_0\sim$ $1.4 cm/MW$ and a nonlinear index $\gamma \sim -5.5 \times10^{-11} cm^2/W$ to fit the data.Comment: 10 pages, 2 figures. Accepted and to appear in Applied Physics Letter

SYNTHESIS, CHARACTERIZATION, IN VITRO ANTIMICROBIAL, ANTHELMINTIC AND DOCKING STUDIES OF NEW 2-[(E)-{[4-(1H-1,2,4-TRIAZOL-1 YLMETHYL)PHENYL]IMINO} METHYL]PHENOL, AND THEIR COMPLEXES WITH 3D METAL IONS

Objective: The main objectives of this research work is the synthesis and characterization of biologically potential triazole ring containing the Schiff base legend and their transition metal complexes, followed by screenings of their antimicrobial and anthelmintic activity the results of antimicrobial activity were compared with docking scores.Methods: The coordination complexes of Co(II), Cu(II), Fe(III) and Zn(II) with Schiff base derived ligand 4-(1H-1,2,4-triazol-1-ylmethyl) aniline and substituted aldehydes have been synthesized. The complexes are characterized by elemental analysis, conductivity measurements, electronic, IR, and 1H NMR spectral data. The synthesized compounds were also screened In vitro antimicrobial activity was carried out according to diffusion method by using agar and potato dextrose agar at 100, 500 and 700 mg/ml concentrations in DMF. HEX 8.0 programmers were used to perform the docking experiments on nucleotide of S. typhi at as ligand [PDB: 3B6O].Results: Schiff base ligand and their transition metal complexes were studied for antimicrobial activity as well as docking. The results of both studies concluded that 4a, 4c and 4d compounds are more active in minimum inhibition concentration (30μg/ml) against Staphylococcus aureus (S. aureus), Salmonella typhi (S. typlei) bacteria and Penicillium chrysogenum (P. Crysogenum) fungi. The compounds showed highest docking score (-257.47,-275.61 and-280.17 respectively) with the secondary structure of the alpha-amylase with a nucleotide from s. typhi in the solid model. In the study of anthelmintic activity among these three compounds, 4d compound exhibits more activity compared with the standard.Conclusion: The compounds 4a, 4c and 4d were found to be more promising pharmacological activity this observation may promote a further development of this triazole group of compounds which may lead to better pharmacological profile than standard drugs. Â

Clinicopathological analysis of ovarian tumours: a 10 year retrospective study

Background: Ovarian tumors account for 30% of all cancers of female genital tract which represents the sixth most common cancer and fourth leading cause of death in women. The present study was done with an objective to determine the frequency and distribution of various ovarian tumors and to study their clinical and histopathological presentations.Methods: It is a retrospective observational study of patients with ovarian tumors subjected to surgery in the department of obstetrics and gynecology, SDM College of Medical Sciences and Hospital from January 2005 to December 2015.Results: There were 642 cases comprising of 77.7% of neoplastic lesions and 22.3% of non-neoplastic lesions. Majority of the ovarian tumors (83%) were seen in the age group of 20 to 50 years. Mean age for ovarian tumors was 38 years.  Among the neoplastic lesions 84% were benign, 14.2% were malignant and 1.8% were borderline tumors. Surface epithelial tumors were the commonest tumors (60.9%) followed by germ cell tumors (12.8%).  Serous cystadenoma was the most common benign tumors (47.1%) followed by mucinous cystadenoma (18.4%). Among the ovarian malignant tumors; serous cystadenocarcinoma was the most common (4.5%) followed by mucinous cystadenocarcinoma (2.6%). Chocolate cysts were the most common among the non-neoplastic lesions (36.4%).Conclusions: Ovarian neoplastic lesions were more common than non-neoplastic lesions. Benign ovarian tumors were common in reproductive age group.  The mean age of occurrence for ovarian tumor was 38 years. The most common neoplasm was surface epithelial tumors, of which serous tumors was the commonest. Chocolate cysts were the most frequently encountered histopathological finding among the non-neoplastic lesions

Clustering Based Energy Efficient Routing for Wireless Sensor Network Using Particle Swarm Optimization

The clustering strategy is the most effective and efficient way to preserve energy in the Wireless Sensor Network (WSN). However, the cluster heads in the hierarchical clustering approach use the majority of the energy that is required to carry out the operations. These operations include receiving the data from the sensor nodes, aggregating it, and then eventually transmitting it to the base station. When choosing the appropriate cluster head, you can play a significant part in reducing the amount of energy that is consumed by the WSN and, as a result, extending its lifespan. A technique for the selection of energy-efficient cluster heads that is based on the particle swarm optimization method is proposed in this study (PSO-EECH). For the method that has been proposed to measure the amount of energy used, we need to take into account the cluster distance, the distance between each sensor node and the nodes that are nearby, and the amount of residual energy that is left in sensor nodes. The aforementioned structure is also capable of doing cluster building, in which the non-cluster head node can follow its CH based on the determined weight function. The proposed PSO-EECH approach has been put through extensive testing, and the results have shown that it possesses a high degree of accuracy in every scenario. The outputs of the proposed algorithm are compared with those of other clustering-based algorithms already in existence, and the conclusions of this comparison have reported that our method outperforms the other existing methods

A Novel Gabor Filtering and Adaptive Histogram Equalization Method for Improving Images

The correct information may only sometimes be effectively conveyed by images due to various factors, such as excessively bright or dark lighting and low or high contrast. As a result, picture improvement has become an essential part of digital image processing. This proposed method aims to develop an algorithm for improving photos captured in dark environments. This letter presents a new picture-enhancing approach that combines median and Gabor filtering using the wavelet domain with histogram equalization working over a spatial domain. The proposed method in this paper combines spatial and transformed domains for image enhancement and has been simulated using MATLAB. The simulation results of two different photos show that the suggested approach extends the histogram over a wide range of grayscale, offering a superior improvement to the original image. The novel proposed algorithm aims to improve image quality and visibility, making identifying essential details within the image easier. Further, the proposed technique's success is manifested by examining the produced photos' contrast and brightness. The findings reveal that the suggested technique beats the other strategies for improving low-contrast photos

Graphene analogue BCN: femtosecond nonlinear optical susceptibility and hot carrier dynamics

Third-order nonlinear absorption and refraction coefficients of a few-layer boron carbon nitride (BCN) and reduced graphene oxide (RGO) suspensions have been measured at 3.2 eV in the femtosecond regime. Optical limiting behavior is exhibited by BCN as compared to saturable absorption in RGO. Nondegenerate time-resolved differential transmissions from BCN and RGO show different relaxation times. These differences in the optical nonlinearity and carrier dynamics are discussed in the light of semiconducting electronic band structure of BCN vis-\`a-vis the Dirac linear band structure of graphene.Comment: 18 pages, 5 figure