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

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

Critical exponents and the correlation length in the charge exchange manganite spin glass Eu_{0.5}Ba_{0.5}MnO_{3}

The critical regime of the charge exchange (CE) manganite spin glass Eu_{0.5}Ba_{0.5}MnO_{3} is investigated using linear and non linear magnetic susceptibility and the divergence of the third ordered susceptibility (chi{_3}) signifying the onset of a conventional freezing transition is experimentally demonstrated. The divergence in chi{_3}, dynamical scaling of the linear susceptibility and relevant scaling equations are used to determine the critical exponents associated with this freezing transition, the values of which match well with the 3D Ising universality class. Magnetic field dependence of the spin glass response function is used to estimate the spin correlation length which is seen to be larger than the charge/orbital correlation length reported in this system.Comment: 4 pages, 4 Figure

Kinematical Analogy for Marginal Dyon Decay

We describe a kinematical analogy for the marginal decay of 1/4-BPS dyons in 4-dimensional N=4 string compactifications. In this analogy, the electric and magnetic charges play the role of spatial momenta, the BPS mass plays the role of energy, and 1/2-BPS dyons correspond to massless particles. Using SO(12,1) "Lorentz" invariance and standard kinematical formulae in particle physics, we provide simple derivations of the curves of marginal stability. We also show how these curves map into the momentum ellipsoid, and propose some applications of this analogy.Comment: 10 pages, minor revision

An optimal VM Placement, Energy Efficient and SLA at Cloud Environment - A Comparative Analysis

In the cloud computing framework, computing resources can be increased or decreased in response to the users’ different application loads. The data is stored and the applications are running on the servers in the clouds. Users do not have to worry about lost or corrupt data. The clouds can distribute computing resources according to the users’ needs or preferences to provide fl exible management. Users do not have to buy expensive computing devices. They only need to pay for the computing services provided by the clouds. Cloud computing provides a platform for computational experiments with abundant computing and storage resources. The system can be considered as a whole and the control and management decisions are sent as services to agents. The challenge in the present study is to reduce energy consumption thus guarantee Service Level Agreement (SLA) at its highest level

Correlation, Network and Multifractal Analysis of Global Financial Indices

We apply RMT, Network and MF-DFA methods to investigate correlation, network and multifractal properties of 20 global financial indices. We compare results before and during the financial crisis of 2008 respectively. We find that the network method gives more useful information about the formation of clusters as compared to results obtained from eigenvectors corresponding to second largest eigenvalue and these sectors are formed on the basis of geographical location of indices. At threshold 0.6, indices corresponding to Americas, Europe and Asia/Pacific disconnect and form different clusters before the crisis but during the crisis, indices corresponding to Americas and Europe are combined together to form a cluster while the Asia/Pacific indices forms another cluster. By further increasing the value of threshold to 0.9, European countries France, Germany and UK constitute the most tightly linked markets. We study multifractal properties of global financial indices and find that financial indices corresponding to Americas and Europe almost lie in the same range of degree of multifractality as compared to other indices. India, South Korea, Hong Kong are found to be near the degree of multifractality of indices corresponding to Americas and Europe. A large variation in the degree of multifractality in Egypt, Indonesia, Malaysia, Taiwan and Singapore may be a reason that when we increase the threshold in financial network these countries first start getting disconnected at low threshold from the correlation network of financial indices. We fit Binomial Multifractal Model (BMFM) to these financial markets.Comment: 32 pages, 25 figures, 1 tabl

The cost of stochastic resetting

Resetting a stochastic process has been shown to expedite the completion time of some complex task, such as finding a target for the first time. Here we consider the cost of resetting by associating a cost to each reset, which is a function of the distance travelled during the reset event. We compute the Laplace transform of the joint probability of first passage time $t_f$, number of resets $N$ and resetting cost $C$, and use this to study the statistics of the total cost. We show that in the limit of zero resetting rate the mean cost is finite for a linear cost function, vanishes for a sub-linear cost function and diverges for a super-linear cost function. This result contrasts with the case of no resetting where the cost is always zero. For the case of an exponentially increasing cost function we show that the mean cost diverges at a finite resetting rate. We explain this by showing that the distribution of the cost has a power-law tail with continuously varying exponent that depends on the resetting rate.Comment: 22 pages, 7 figure

The Buzz Button to your Toothache – Spilanthes acmella : A Review

Spilanthes acmella, commonly known as toothache plant, is an important medicinal plant belonging to family Asteraceae. It has been reported to possess various biological activities like anti-pyretic, antidiuretic, anti-inflammatory, anti-oxidant, immunomodulatory, hepatoprotective, anticancer and antitoothache etc. The bioactive chemical component is spilanthol, an alkamide which is present in roots and all aerial parts of the plant. Spilanthol has high industrial demand for its use in pharmaceutical, cosmetic and toothpaste industry. S.acmella is quickly getting depleted from its natural habitat, because of its wider applications for commercial use

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