V.K. Jayasree

Bio: V.K. Jayasree is an academic researcher from Cochin University of Science and Technology. The author has contributed to research in topics: Photoplethysmogram & Gain-switching. The author has an hindex of 2, co-authored 2 publications receiving 32 citations.

Study of solvent effect in laser emission from Coumarin 540 dye solution.

Abstract: The results of a brief investigation of the amplified spontaneous emission and lasing characteristics of Coumarin 540 dye in as many as ten different solvents are reported. It has been found that C 540 dye solutions contained within a rectangular quartz cuvette give laser emission with well resolved equally spaced modes when pumped with a 476 nm beam. The modes were found to originate from the subcavities formed by the plane-parallel walls of the cuvette containing the high-gain medium. While the quantum yield remains a decisive factor, a clear correlation between the total width of the emission spectra and the refractive indices of the solvents of the respective samples has been demonstrated. The well-resolved mode structure exhibited by the emission spectra gives clear evidence of the lasing action taking place in the gain medium, and the number of modes enables us to compare the gain of the media in different samples. A detailed discussion of the solvent effect in the lasing characteristics of C540 in different solutions is given.

Design and Development Of a Simple Hardware Setup for Sensing Blood Volume Pulse and a PIC Microcontroller Based Heart Rate Meter

Abstract: This paper describes the design and development of a simple hardware setup for recording the blood volume pulse from the finger tip using transmission mode of photoplethysmography (PPG). PPG is known for its simple construction, ease of use and cost effectiveness and can provide information about the changes in the respiratory and cardiac activity and as well aid in earlier non-invasive diagnostics. The blood volume pulse has two components-one a systolic peak which mainly reflects the heart condition and activity, while the other which is called the diastolic peak determines the elasticity and other features of the vascular system. Since one blood volume pulse is generated for each heart beat, a PIC microcontroller is used to measure the heart rate. The wavelet denoising algorithm is used to suppress the noise component in the PPG signal. For heart rate estimate comparison, PPG signals are evaluated by comparing their beat-to-beat estimates with the corresponding R-R intervals from an electrocardiogram (ECG).

Organic Solvent Effects in Biomass Conversion Reactions.

Abstract: Transforming lignocellulosic biomass into fuels and chemicals has been intensely studied in recent years. A large amount of work has been dedicated to finding suitable solvent systems, which can improve the transformation of biomass into value-added chemicals. These efforts have been undertaken based on numerous research results that have shown that organic solvents can improve both conversion and selectivity of biomass to platform molecules. We present an overview of these organic solvent effects, which are harnessed in biomass conversion processes, including conversion of biomass to sugars, conversion of sugars to furanic compounds, and production of lignin monomers. A special emphasis is placed on comparing the solvent effects on conversion and product selectivity in water with those in organic solvents while discussing the origins of the differences that arise. We have categorized results as benefiting from two major types of effects: solvent effects on solubility of biomass components including cellulose and lignin and solvent effects on chemical thermodynamics including those affecting reactants, intermediates, products, and/or catalysts. Finally, the challenges of using organic solvents in industrial processes are discussed from the perspective of solvent cost, solvent stability, and solvent safety. We suggest that a holistic view of solvent effects, the mechanistic elucidation of these effects, and the careful consideration of the challenges associated with solvent use could assist researchers in choosing and designing improved solvent systems for targeted biomass conversion processes.

Ultralow-threshold multiphoton-pumped lasing from colloidal nanoplatelets in solution

Abstract: Multiphoton-pumped lasing from semiconductor nanocrystals in solution is difficult due to Auger recombination, low volume fraction and high threshold. Here, Li et al. demonstrate photostable, ultralow threshold multi-photon pumped lasing from colloidal CdSe/CdS nanoplatelets in a Fabry-Perot optical resonator.

Non-covalent interactions of coumarin dyes with cucurbit[7]uril macrocycle: modulation of ICT to TICT state conversion

Abstract: Non-covalent interaction of coumarin laser dyes, namely coumarin-1 (C1), coumarin-481 (C481) and coumarin-6H (C6H), with a versatile macrocyclic host molecule cucurbit[7]uril (CB7), has been investigated in aqueous solution using photophysical methods. Steady-state and time-resolved fluorescence studies illustrate significant enhancements/modifications in the fluorescence yields, lifetimes and spectral features of C1, C481 and C6H on interaction with CB7, and are assigned to 1 : 1 complex formation between the dyes and the CB7 host. The complex formation is mainly driven by charge–dipole interaction, as evident from the binding constant values (K ∼ 104–105 M−1). The large changes in the excited state behaviour of C1 and C481 as compared to C6H in the presence of CB7 indicate that CB7 binds C1 and C481 through the encapsulation of the 7-N,N′-diethylamino group of the dyes and the structural rigidity imposed by this interaction dramatically alters the excited state properties of the dyes by preventing the conversion of their emissive intramolecular charge transfer (ICT) state to the non-radiative twisted intramolecular charge transfer (TICT) state. The present results direct towards the probable supramolecular approach using water soluble macrocyclic CB7, in the development of aqueous dye laser systems in the blue-green region.

Intriguing H-aggregate and H-dimer formation of coumarin-481 dye in aqueous solution as evidenced from photophysical studies.

Abstract: Photophysical properties of coumarin-481 (C481) dye in aqueous solution show intriguing presence of multiple emitting species. Concentration and wavelength dependent fluorescence decays and time-resolved emission spectra and area-normalized emission spectra suggest the coexistence of dye monomers, dimers, and higher aggregates (mostly trimers) in the solution. Because of the efficient intramolecular charge transfer (ICT) state to twisted intramolecular charge transfer (TICT) state conversion, the dye monomers show very short fluorescence lifetime of ∼0.2 ns. Fluorescence lifetimes of dimers (∼4.1 ns) and higher aggregates (∼1.4 ns) are relatively longer due to steric constrain toward ICT to TICT conversion. Observed results indicate that the emission spectra of the aggregates are substantially blue-shifted compared to monomers, suggesting H-aggregation of the dye in the solution. Temperature-dependent fluorescence decays in water and time-resolved fluorescence results in water–acetonitrile solvent mixture...

A Spectroscopic and DFT Study of the Electronic Properties of Carbazole-Based D–A Type Copolymers

Abstract: The structural and electronic properties of three carbazole containing copolymers used in organic photovoltaic applications, poly[N-1-octylnonyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT), poly[N-1-octylnonyl-2,7-carbazole-alt-4,7-(2′,1′,3′-benzothiadiazole)] (PCBT), and poly[N-1-octylnonyl-2,7-carbazole-alt-4,7-(2′,1′,3′-benzoselenadiazole)] (PCBSe) have been studied using resonance Raman (RR) and transient absorption (TA) spectroscopies and density functional theory (DFT) calculations. Enhancement of Raman modes centered on the acceptor unit when a Raman excitation wavelength is coincident with lowest energy electronic excitation suggests that the excitation involves charge transfer from the carbazole donor to the varying benzodiazole acceptors. The pattern of the enhancement when the excitation wavelength is coincident with the higher energy transition indicates that this transition is π to π* in nature; this is consistent with TD-DFT calculations. Nanosecond transie...