Potential for Nile red dye-based analysis of microplastics from oceanic samples.

The Global production of plastics has exceeded over 300 million metric tons. Billions of tons of plastic waste that is generated gets accumulated as plastic debris in soil, sediments, oceans and surface water with no obvious strategy to tackle them. The plastics disposed in the water and land ultimately disintegrate to microplastics, widely accepted as particles [less than]5 mm size. These microplastics are ubiquitous contaminants prevalent in the environment and pose great ecological hazard. Ensuring sustainability of coastal marine areas worldwide and reducing biodiversity loss has long been identified as a global challenge. However, dearth of scientific strategies and standardized protocols for fast and accurate detection of microplastics is a matter of concern and needs immediate attention. Therefore, robust, reliable and high through-put detection method for microplastics in oceanic environment is highly sought after. Quite a few studies have explored the potential of Nile red a solvatochromic dye in detection of microplastics. However, often Nile red alone cannot be used in quantifying microplastic due to false positives generated by staining of organic matter. In this work, we have adopted a method based on costaining of microplastics using Nile red dye and Methylene blue by fluorescence microscopy. We have observed that Nile red overestimated microplastic particles and this study serves as foundation to our future work

Logarithmic scaling in the near-dissipation range of turbulence

A logarithmic scaling for structure functions, in the form $S_p \sim [\ln (r/\eta)]^{\zeta_p}$, where $\eta$ is the Kolmogorov dissipation scale and $\zeta_p$ are the scaling exponents, is suggested for the statistical description of the near-dissipation range for which classical power-law scaling does not apply. From experimental data at moderate Reynolds numbers, it is shown that the logarithmic scaling, deduced from general considerations for the near-dissipation range, covers almost the entire range of scales (about two decades) of structure functions, for both velocity and passive scalar fields. This new scaling requires two empirical constants, just as the classical scaling does, and can be considered the basis for extended self-similarity

Unified Multifractal Description of Velocity Increments Statistics in Turbulence: Intermittency and Skewness

The phenomenology of velocity statistics in turbulent flows, up to now, relates to different models dealing with either signed or unsigned longitudinal velocity increments, with either inertial or dissipative fluctuations. In this paper, we are concerned with the complete probability density function (PDF) of signed longitudinal increments at all scales. First, we focus on the symmetric part of the PDFs, taking into account the observed departure from scale invariance induced by dissipation effects. The analysis is then extended to the asymmetric part of the PDFs, with the specific goal to predict the skewness of the velocity derivatives. It opens the route to the complete description of all measurable quantities, for any Reynolds number, and various experimental conditions. This description is based on a single universal parameter function D(h) and a universal constant R*.Comment: 13 pages, 3 figures, Extended version, Publishe

Development of a ring cavity-based fibre optic sensor for MR-compatible medical sensing applications.

Advances in robotic systems and rapid developments in minimally invasive surgery (MIS) have made their use possible in the operating room due to many distinct advantages offered by MIS over conventional surgical procedures. The constant increase of medical examinations, surgeries and surgical interventions using intraoperative guidance with magnetic resonance imaging (MRI) has promoted research on new sensors to be applied in this scenario. However, due to the challenging environment under MRI system limits the applicability of materials and traditional electronic sensors. Optical fibres are small in size, chemically inert, immune to electromagnetic interference and offer the real-time in vivo multi-parameter measurement capability. Herein, we report a ring cavity-based fibre optic sensor design using MR-compatible polymer material. Optical fibres were used to excite surface resonance modes (SRM) of the ring cavity-based sensor. The paper reports initial investigations on ring cavity based MR-compatible fibre optic sensor design. Computational simulations were carried out to study the effect of structural and material parameters on the sensor design. Ring cavity was developed using polymethyl methacrylate. Developed ring cavity will be used to develop the MR-compatible fibre optic sensor for medical applications

Angular dependent light emission from planar waveguides.

We have investigated the angular dependence of amplified spontaneous emission (ASE) and laser emission from an asymmetric and free-standing polymer thin films doped with rhodamine 6G, which is transversely pumped by a pulsed Nd:YAG laser. A semi-leaky waveguide or quasi-waveguide structure has been developed by spin coating technique. In these waveguides, the light was confined by the film/air-film/glass substrate interfaces. At the film/substrate interface, a portion of light will reflect back into the film (guided mode) and the remaining refracted to the substrate resulting in cutoff modes. A blue-shift in ASE has been observed when the pump power was increased from 8 to 20 mW allowing a limited range of tuning of emission wavelength. To study the directionality of the ASE from the waveguide, we have measured the output intensity and FWHM of emission spectra as a function of viewing angle (θ) from the plane parallel to film. From the detailed examination of the output emission spectra, as +θ increases from 0° there has been an initial decrease in output intensity, but at a particular angle ≈10° an increase in output intensity was observed. This additional peak in output intensity as +θ is a clear indication of coexistence of the cutoff mode. We also present a compact solid-state laser based on leaky mode propagation from the dye-doped polymer free-standing film (∼50-μm thickness) waveguide. The partial reflections from the broad lateral surfaces of the free-standing films provided the optical feedback for the laser emission with high directionality. For a pump power of 22 mW, an intense line with FWHM-[less than] 0.2nm was observed at 578nm

Disorder, Order, and Domain Wall Roughening in the 2d Random Field Ising Model

Ground states and domain walls are investigated with exact combinatorial optimization in two-dimensional random field Ising magnets. The ground states break into domains above a length scale that depends exponentially on the random field strength squared. For weak disorder, this paramagnetic structure has remnant long-range order of the percolation type. The domain walls are super-rough in ordered systems with a roughness exponent $\zeta$ close to 6/5. The interfaces exhibit rare fluctuations and multiscaling reminiscent of some models of kinetic roughening and hydrodynamic turbulence.Comment: to be published in Phys.Rev.E/Rapid.Com

Solvent effects on lasing characteristics for Rh B laser dye.

We demonstrate pulsed, photopumped multimode laser emission in the visible spectral range from rhodamine B dye dissolved in various solvents. The laser emission is characterized by a well-defined, low threshold pump power at which the emission spectral intensity dramatically increases and collapsed into several dominant laser modes with reduced mode spacing and spectral width. The modes were found to originate from the subcavities formed by the plane-parallel walls of the cuvette containing the gain medium. The cavity lasing spectral structure and the numbers of longitudinal modes were easily controlled by changing the solvents. A shift in the emission spectra has been also observed by changing the solvents will allow a limited range of tuning of laser emission wavelength. We also determined the gain coefficient and stimulated emission cross-section for the Rh B dye dissolved liquid laser system. A detailed discussion of the solvent effect in the lasing characteristics of Rh B in different solution is explained along with the computational data

Studies on the melting of simple DNA polymers

The modified self-consistent phonon approximation (MSPA) has been fairly successful in predicting the melting temperatures of simple DNA polymers. In the first part of this thesis we analyze how the method works, based on free energy calculations. The analysis is very much like the Landau analysis of displacive phase transitions. We also discuss the meaning of a soft mode form of melting. There are several reasons to expect that poly(dA) $\cdot$ poly(dT) would melt at a lower temperature than poly(dAT) $\cdot$ poly(dAT). The opposite is both observed and is also the result of an MSPA calculation. The second part of this thesis explores the reason for the inversion in melting behavior that is predicted by MSPA. Vibrational states tend to accumulate in smaller frequency regions in poly(dAT) $\cdot$ poly(dAT). This seems to be the dynamical reason for its lower melting temperature. One effect of thermal fluctuations in a DNA molecule is to reduce the hydrogen bond force constants in the vicinity of the fluctuation. In the third part of this thesis we study this effect of thermal fluctuations on the vibrational spectra of poly(dG) $\cdot$ poly(dC) and poly(dA) $\cdot$ poly(dT). We assume the fluctuations create a defect (decrease in h-bond force constants) that is localized to a single base pair. In both polymers the presence of such a defect induces prominent defect modes in the frequency region between 60 and 72 cm\sp{-1}. The mode found in poly(dG) $\cdot$ poly(dC) is quasi-local (in-band) whereas the mode found in poly(dA) $\cdot$ poly(dT) is local (lies in the band gap). Our calculations indicate that it is easier to create the defect mode in poly(dA) $\cdot$ poly(dT) than in poly(dG) $\cdot$ poly(dC). The local mode in poly(dA) $\cdot$ poly(dT) is at a frequency where infrared absorption occurs