Absorption Phenomena Research Articles

Modeling thin layers of analytes on substrates for spectral analysis: use of solid/liquid n and k values to model reflectance spectra

Since solids are only sometimes seen en masse in a pure bulk form, and for liquids other than water almost never, a capability to model reflectance spectra from analytes deposited on various substrates would be highly advantageous. If available, the real, n ( ν ) , and imaginary, k ( ν ) , components of the complex refractive index, n∼ = n + ik, can be used to simulate infrared spectra, accounting for reflection, refraction, and absorption phenomena as a function of wavelength. We focus on using the Pacific Northwest National Laboratory (PNNL) derived n / k vectors for solid and liquid analytes deposited as thin layers on different types of substrates including conductors, such as aluminum, and inorganic dielectrics, such as glass. The model is an adaptation of the Monte Carlo ray trace modeling program, TracePro, extended through the use of its macrolanguage. The model is tested using thin films of organic liquids including silicone oil and no. 2 diesel fuel, as well as organic solids such as caffeine and acetaminophen on aluminum and glass. The predicted spectra for the solid films were compared to experimental hemispherical reflectance data measured using a Fourier transform spectrometer with an integrating sphere. The thickness of the calculated layer is a parameter for predicting the (transflectance) spectra and is obtained using the areal density measured from gravimetric methods to generate the thin-layer samples. Comparison of the calculated spectra with experimental hemispherical reflectance data shows excellent agreement, indicating promise for the use of measured n / k data to synthesize reference spectral data. In particular, accounting for the inhomogeneity of the deposits greatly improved the match with experimental data. Finally, the theoretical modeling shows that for thicker layers (ca. 20 to 100 μm) of typical organics possessing moderately strong k values, the longwave infrared features are often saturated and better spectral contrast is obtained from the overtone/combination bands in the shortwave infrared.

Inversion Method Characterization of Graphene-Based Coordination Absorbers Incorporating Periodically Patterned Metal Ring Metasurfaces.

In this paper, we propose a tunable coordinated multi-band absorber that combines graphene with metal–dielectric–metal structures for the realization of multiple toward perfect absorption. The parametric inversion method is used to extract the equivalent impedance and explain the phenomena of multiple-peak absorption. With the change of the Fermi level, equivalent impedances were extracted, and the peculiarities of the individual multiple absorption peaks to change were determined. By changing the structure parameters of gold rings, we obtain either multiple narrow-band absorption peaks or a broadband absorption peak, with the bandwidth of 0.8 μm where the absorptance is near 100%. Therefore, our results provide new insights into the development of tunable multi-band absorbers and broadband absorbers that can be applied to terahertz imaging in high-performance coordinate sensors and other promising optoelectronic devices.

CO2 absorption into aqueous diethanolamine solution with nano heavy metal oxide particles using stirrer bubble column: Hydrodynamics and mass transfer

Abstract In this research, the TiO2, ZnO, and ZrO2 nanofluids based on the DEA solution were provided exploiting the ultrasonic dispersion system to investigate the impact of the nano-particles on the CO2 absorption in a continuously stirred bubble column. The nano-particle concentration was determined in the range 0.01−0.10 wt%,. Bubble size distribution along column axis measurements was carried out using the high-speed digital camera. The influences of several factors such as CO2 partial pressure, solid loading, nanoparticle type, and stirring speed on the hydrodynamic characteristics and CO2 absorption performance were examined in detail. The presence of nanoparticles increased the gas holdup and interfacial area up to optimum value and then had a negligible effect. The stirrer speed increased the gas holdup and interfacial area up to optimum value and then decreased. Furthermore, the results showed that the adding nanoparticles in the range of 0.01−0.1 wt% increased CO2 absorption efficiency between 25.2–43.8% and the optimum value of nanoparticles can be an effective key parameter at the absorption phenomena into a dilute amine solution. Also, it was determined that at optimum stirrer speed, the removal efficiency of ZnO, TiO2, and ZrO2 nanofluids was caused an increase of about 12.1 % 8.0 %, and 13.3 %, respectively.

Lithium carbonate precipitation by homogeneous and heterogeneous reactive crystallization

Lithium carbonate precipitation from a Li2SO4 solution in a stirred crystallizer in semi-batch processes was investigated and compared using a heterogeneous CO2 reaction and homogeneous Na2CO3 reaction. Nucleation and crystal growth were successfully monitored by an inline Particle Track based on the focused beam reflectance measurement technique. The results obtained indicate that the particle size decreased with an increase in mixing speed for both precipitation processes. However, the CO2 feed rate in the heterogeneous reaction and the pumping rate of Na2CO3 in the homogeneous reaction did not have a significant impact on the particle size distribution. Temperature and the final pH play critical roles in precipitation when using CO2 as a reactant. High alkaline conditions are needed to induce heterogeneous precipitation. The lithium recovery with homogeneous precipitation was higher than with heterogeneous precipitation, probably due to the gas-liquid mass transfer phenomena of absorption influencing carbon dioxide conversion to carbonate ions in heterogeneous precipitation. Agglomerates of leaf-shaped primary crystals were mainly obtained.

Numerical simulation of trickle bed reactors for biological methanation

Biological methanation in trickle bed reactors is an auspicious approach to convert hydrogen and carbon dioxide into methane. In order to analyze this process, a comprehensive CFD model was implemented including multiphase flow, absorption, and reaction phenomena. The model is based on the Eulerian-Eulerian method. Experimental investigations and literature data serve as its validation. The experiments focused on the hydrodynamics of a trickle bed composed of clay granulate and the applied reactor enabled detailed measurements of radial liquid flow profiles and liquid holdup dependent on the overall volume flow rate. The simulation of liquid dispersion confirms the experimental results regarding averaged macroscopic fluid flow. However, liquid holdup is slightly underestimated by the computational model. In addition to the hydrodynamic investigation, simulation of biological methanation provide insight into mutual interactions between multiphase flow and biochemical conversion and present a methane production rate on the same order of magnitude as literature values.

Strong two-photon absorption in ErFeO3 thin films studied using femtosecond near-infrared Z-scan technique

Ultrafast nonlinear optical (NLO) characterization of ErFeO3 thin films deposited by the solgel assisted spin coating technique is reported herein. In the present investigation, we have used femtosecond (fs) pulses for studying the nonlinear absorption and refraction properties of ErFeO3 thin films. Intensity dependent open and closed aperture Z-scan experiments were performed on ErFO3 films in the visible and near-infrared wavelengths of 600 nm, 800 nm, and 1200 nm. To explain the observed NLO results, phenomenological models of simultaneous multi-photon and excited sate absorption are developed for three-level model systems suitable for excitation wavelengths with (600 and 800 nm) and without (1200 nm) linear absorption, respectively. Optical limiting (OL) characteristic is shown to exist through the phenomenon of two-photon absorption in a certain intensity range at the three wavelengths and under the simultaneous saturation of linear absorption at 600 nm and 800 nm. The upper limit of the intensity for OL applications is demonstrated by the saturation effect. The non-linear absorption results are correlated with the linear absorption at these wavelengths, which involves electronic transitions between Fe d- and O p-orbitals.

Manufacturing of cellulose-based paper: dynamic water absorption before and after fiber modifications with hydrophobic agents

Absorption of liquid or vapor water in paper designed for conversion processes is a critical phenomenon. In particular, the dimensional stability of the paper as the water content changes is crucial for the success of all the conversion processes, including copying and printing. Appropriate chemical treatments of the fibers can limit the phenomena of water absorption, allowing a better workability of the paper substrates. In the present study, moisture absorption tests were conducted under isothermal conditions on untreated papers and treated by coatings with silane, organo-siloxane and silicone agents, as well as with polyelectrolytes using layer-by-layer techniques. The treated and untreated papers were tested by changing the relative humidity between 0 and 80% relative humidity. The Guggenheim–Anderson–de Boer model was used to study moisture absorption isotherms, showing the increase in the dimensional stability of the papers after the chemical treatments of the fibers.

The synthesis and characterisation of curcumin loaded Ag (1-X) Ni X Fe2 O4 for drug delivery

ABSTRACT A simple procedure of solvothermal synthesis of Silver doped Nickel ferrite nanoparticle is described in this paper for the application of drug delivery. The microwave absorption and SERS phenomena of silver nanoparticles and water-absorbent property of the polymer material such as polyethylene glycol (PEG) to bypass fast identification by the antibodies are made use in the synthesis of Ag-doped nickel ferrite with PEG as a solvent. The ferrite sample was distinguished using XRD, FTIR, SEM, TEM, and VSM. The absorption wavelength and corresponding band gap energy were calculated by UV-Vis spectroscopy. The drug delivery efficiency of silver doped nickel ferrite sample was conducted with curcumin by changing pH, initial drug concentration and specified magnetic field. Results prove that the addition of silver and polyethylene glycol in nickel ferrites changes the properties of the nanoparticle and recognised as a good material for drug delivery applications.

Oblique derivative problems and Feller semigroups with discontinuous coefficients

This paper is devoted to the functional analytic approach to the problem of existence of Markov processes with an oblique derivative boundary condition for second-order, uniformly elliptic differential operators with discontinuous coefficients. More precisely, we construct Feller semigroups associated with absorption, reflection, drift and sticking (or viscosity) phenomena at the boundary. The approach here is distinguished by the extensive use of the ideas and techniques characteristic of the recent developments in the Calderon–Zygmund theory of singular integral operators with non-smooth kernels.

Ferromagnetic Resonance in Electroplated CuBe/FeCoNi and Amorphous CoFeSiB Wires

Ferromagnetic wires are widely used in microwave technologies. In this work, impedance studies were carried out in a wide range of microwave frequencies (from 0.1 to 20 GHz). By compensating the parameter $\boldsymbol S_{11}$ for the length of the adapter and the holder, it was possible to ensure the inductive nature of the wire impedance up to the frequency of 14 GHz. As a result, the wire response was described as a lossy inductance, and the inductive resistance of which changes by the $\Delta {X}$ value and the active resistance by $\Delta $ R value under the influence of an external constant magnetic field. We were able to approximate $\Delta $ X and $\Delta $ R changes with the real and imaginary parts of the diagonal component of the magnetic susceptibility tensor, obtained from the Landau–Lifshitz equation with a Gilbert damping term for ferromagnetic resonance (FMR), and determine the FMR parameters in the microwave region. It was also possible to separate the FMR region from the region of such microwave absorption phenomena as magnetoimpedance. An optimized system based on the vector network analyzer ZVA-67 was designed and tested. It allowed to determine experimentally the parameters of magnetoimpedance and FMR of the electroplated FeCoNi/CuBe and rapidly quenched CoFeSiB amorphous wires measured by the same device and in the same configuration in a single-frequency scan. A prototype of the magnetic field sensor has been proposed and tested.

Electrodynamic simulation of laser beam propagation in waterjet-guided laser processing

Waterjet-guided material processing is a technique that combines the capabilities of laser material processing with water jetting. In this study, we have investigated laser beam propagation in a waterjet column by numerically solving the Maxwell equations and the heat equation. A 1064 nm laser and its frequency-doubled 532 nm laser were chosen for the simulations, and the finite-difference time-domain (FDTD) method was employed for solving the Maxwell equations. The coupling effect of the laser and waterjet was simulated with different numerical apertures and different waterjet column diameters. Extensive investigations on laser absorption phenomena regarding the outer surface geometries of the waterjet (cylindrical shape with and without sinusoidal perturbation), and temperature distributions were also conducted. To the best of the authors' knowledge, this is the first electrodynamic simulation of laser beam propagation and interaction with a water column in waterjet-guided laser processing. Some interesting findings concerning laser beam absorption characteristics inside a waterjet column were revealed.

Improved third harmonic nonlinear optical process upon e-beam irradiation in Cl: ZnO thin films

We report the tuning of third-harmonic generation and nonlinear absorption process in Cl doped ZnO (Cl: ZnO) thin films by energetic electron beam irradiation. The structural studies outcomes the stability of the films based on the nominal variations observed in structural parameters on irradiation. The absorption edge shows a redshift at higher irradiation dosage and bandgap of the film shows a drop from 3.28 eV to 3.22 eV at 20 kGy dosages. The morphology of the films has undergone a drastic change on irradiation and grains are found to be shattered and islands are formed at different regions of the scan area. The photoluminescence (PL) spectra show substantial change after the irradiation and number of emissions centres decreased along with peak broadening effect. The studies confirm that radiative defects in the films decreased which in turn give rise to enhancement of non-radiative defects. The Raman spectra depicts three phonon modes E2H-E2L, A1 (TO) and E2H similar to unirradiated films. The E2H mode peak has dominated in all the irradiated films confirming the hexagonal wurtzite structure of the films. On irradiation, the asymmetry observed in the core level O 1s XPS spectra has changed and a single peak positioned around 529.8 eV was observed indicating the quenching of oxygen-related defects. Third harmonic generation studies exhibit an enhancement in the THG intensity upon electron beam incorporation attributed to optical absorption and excitonic effects. Open aperture Z-scan measurement shows a high βeff of 31 × 10-2 cm/W at 20 kGy irradiated films due to enhanced scattering induced nonlinear absorption phenomena. The enhanced nonlinear optical properties exhibited by Cl: ZnO thin films show promising applications of grown material in frequency conversion and optical filtering devices.

Investigation of the Effect of Non-absorbable Gas on Absorption Phenomenon in an Absorption Heat Pump

Investigation of the Effect of Non-absorbable Gas on Absorption Phenomenon in an Absorption Heat Pump

Optomechanically induced transparency, amplification, and fast–slow light transitions in an optomechanical system with multiple mechanical driving phases

We investigate the change in width of transparency windows and the amplification of the probe output spectra in an optomechanical system with multiple mechanical resonators. Each mechanical resonator is driven by a mechanical driving field, and the phases of these mechanical driving fields are different. Via exhibiting the probe output spectra of the system, we find that the number of transparency windows is explicitly decided by the number of mechanical resonators with different frequencies. Meanwhile, we discuss the effect of cavity decay rate on the width of the transparency windows. Moreover, we also investigate the absorption and amplification phenomena with the different phase differences among the pump field, probe field, and mechanical driving fields. By adjusting the phase differences, the fast–slow light transitions can occur. These interesting phenomena can also be exploited to investigate the optical switch and frequency comb generation.

Free vibration analysis of an aluminium honeycomb sandwich panel filled with CFRP tubes – numerical study

ABSTRACT Aluminium honeycomb cores were predominantly used in transportation and aerospace sectors because of its outstanding structural and better mechanical properties. In the recent studies, it was found that carbon fibre-reinforced polymer composites (CFRP) tubes also can be used as a filler material to benefit out an improved mechanical behaviour. Until now, many research studies are done on CFRP-filled honeycomb to analyse the energy absorption phenomenon for axial impact loading. Always there is a demand exists to investigate structure for vibrational loading and frequencies also along with the structural loading. In this paper, numerical free-free vibration analysis has been performed for CFRP-filled honeycomb sandwich panels to analyse and predict the resonance frequencies and Eigen modes by varying the number of CFRP tubes inserted in the honeycomb and varying the honeycomb cell size. Vibrational constants like natural frequency, initial bending mode, initial lateral mode, initial torsion modes and second bending mode of CFRP-filled aluminium honeycomb were investigated.

Modeling the Effect of Temperature on Membrane Response of Light Stimulation in Optogenetically-Targeted Neurons.

Optogenetics is revolutionizing Neuroscience, but an often neglected effect of light stimulation of the brain is the generation of heat. In extreme cases, light-generated heat kills neurons, but mild temperature changes alter neuronal function. To date, most in vivo experiments rely on light stimulation of neural tissue using fiber-coupled lasers of various wavelengths. Brain tissue is irradiated with high light power that can be deleterious to neuronal function. Furthermore, absorbed light generates heat that can lead to permanent tissue damage and affect neuronal excitability. Thus, light alone can generate effects in neuronal function that are unrelated to the genuine “optogenetic effect.” In this work, we perform a theoretical analysis to investigate the effects of heat transfer in rodent brain tissue for standard optogenetic protocols. More precisely, we first use the Kubelka-Munk model for light propagation in brain tissue to observe the absorption phenomenon. Then, we model the optothermal effect considering the common laser wavelengths (473 and 593 nm) used in optogenetic experiments approaching the time/space numerical solution of Pennes' bio-heat equation with the Finite Element Method. Finally, we then modeled channelrhodopsin-2 in a single and spontaneous-firing neuron to explore the effect of heat in light stimulated neurons. We found that, at commonly used light intensities, laser radiation considerably increases the temperature in the surrounding tissue. This effect alters action potential size and shape and causes an increase in spontaneous firing frequency in a neuron model. However, the shortening of activation time constants generated by heat in the single firing neuron model produces action potential failures in response to light stimulation. We also found changes in the power spectrum density and a reduction in the time required for synchronization in an interneuron network model of gamma oscillations. Our findings indicate that light stimulation with intensities used in optogenetic experiments may affect neuronal function not only by direct excitation of light sensitive ion channels and/or pumps but also by generating heat. This approach serves as a guide to design optogenetic experiments that minimize the role of tissue heating in the experimental outcome.

Dynamics and stability of cw and pulse lasers in Kerr optical media with K-photon absorption

The laser dynamics in inscription processes involving transparent media is carried out, by considering an optical field propagating in a transparent medium with Kerr nonlinearity. The study takes into account multi-photon absorption phenomena, as well as a possible modification of the material structure resulting in the generation of a plasma of nearly free electrons. The model is described by a complex Ginzburg–Landau equation governing the laser dynamics, in which an extra Kth-order nonlinear term is induced by K-photon absorption processes. The model also takes into consideration the electron plasma generation via a linear term in the optical field. A global stability analysis of the system dynamics reveals a rich variety of fixed points consisting of no, one or two singular points in the amplitude-frequency plane. The modulational instability of plane waves gives rise to period-halving bifurcations in the continuous-wave amplitude growth rate, reminiscent of dominant multi-pulse structures in the nonlinear regime at large multi-photon absorption rate K. Pulses and multi-pulses are observed in numerical simulations of the nonlinear equations for the full system dynamics, the first structures are clearly associated with the case K = 2 whereas multi-pulse structures of increasing amplitudes and shorter perioids are dominant at larger values of K.

Manipulation of optomechanically induced transparency and absorption by indirectly coupling to an auxiliary cavity mode.

We theoretically study the optomechanically induced transparency (OMIT) and absorption (OMIA) phenomena in a single microcavity optomechanical system, assisted by an indirectly coupled auxiliary cavity mode. We show that the interference effect between the two optical modes plays an important role and can be used to control the multiple-pathway induced destructive or constructive interference effect. The three-pathway interference could induce an absorption dip within the transparent window in the red sideband driving regime, while we can switch back and forth between OMIT and OMIA with the four-pathway interference. The conversion between the transparency peak and absorption dip can be achieved by tuning the relative amplitude and phase of the multiple light paths interference. Our system proposes a new platform to realize multiple pathways induced transparency and absorption in a single microcavity and a feasible way for realizing all-optical information processing.

On competitive gas adsorption and absorption phenomena in thin films of ionic liquids

The equipartition thickness provides a way to design advanced materials with task-specific surface properties and to predict their adsorption performance.

Inter and intra band impurity-related absorption in (In,Ga)N/GaN QW under composition, size and impurity effects

In this paper, we theoretically investigate the impacts of Internal well composition, size and impurity's position on the inter valence-conduction bands and intra conduction band optical absorption in GaN/(In,Ga)N/GaN hetero-structure. Based on the numerically finite element method (FEM), the impurity's related Schrödinger equation is solved for the finite potential barrier considering the dielectric constant and effective-mass mismatches between the well and its surrounding matrix. Our results show that the absorption is strongly governed by the dipole matrix element and initial and final implied states transition energies. For a fixed barrier width, the absorption spectra are found red-shifted (blue-shifted) with increasing the well width (In-concentration). It is also shown that the impurity's absorption phenomenon is more pronounced for the off-center case compared to the on-center one. We conclude that the proper control of these parameters is required to best understanding of the optical absorption for solar cell applications.