Absorption Phenomena Research Articles

Identification of Complex Oxidation/Corrosion Behaviours of Boron Nitride Under High Temperature

To characterize the oxidation/corrosion behaviour of boron nitride (BN) at high temperature and to determine kinetics, thermo-gravimetric analyses were performed on BN flat coatings under dry (80% N2, 20% O2) and wet conditions (10% H2O, 70% N2, 20% O2), at temperatures ranging from 700 to 900 °C. The surface morphology was analysed by scanning electron microscopy. The aim of the study was to understand the complex behaviour of BN at high temperature under wet air. A model was then proposed to explain the recorded mass variations, by taking into account a competition between absorption and volatilization phenomena. Finally, an estimation of the amount of adsorbed species was extracted from these data.

Transient Absorption Phenomena in Synthetic HPHT and CVD Diamonds for a Fast Timing in Nuclear Instrumentation

In this study, we investigate transient phenomena in synthetic diamonds obtained by High Pressure High Temperature and Chemical Vapor Deposition methods. Study was aimed at searching for inorganic crystalline media combining ionizing radiation detecting properties and non-linear absorption of ultra-short laser pulses. The nonlinear pump-and-probe optical absorption technique with of 140 fs laser pulses was used to study the effects.

Realization of controllable photonic molecule based on three ultrahigh‐Q microtoroid cavities

AbstractThree‐cavity photonic molecules have been realized in several platforms, but their structures and configurations are mostly fixed with limited tunability in the coupling strengths and individual resonant frequencies. Here, we demonstrate an experimental realization of a coupled triple‐cavity photonic molecule (TCPM) composed of three independently‐selectable ultrahigh quality microtoroids. By precisely tuning the inter‐cavity coupling strengths (via distances) and the resonant frequencies (via fine temperature control), as well as coupling the tapered optical fiber onto either the side or middle cavity, evolutions of the TCPM's supermodes are fully mapped and analyzed. Interesting phenomena, such as dark state and double anti‐crossing, emerge in this TCPM system. When the quality factors of the cavities are properly chosen, transition from double electromagnetically‐induced transparency to double electromagnetically‐induced absorption phenomena happens. Such fully‐controlled TCPM system sets a stage for future investigations of new physical effects including cavity‐QED with multiple coupled cavities and topologically protected photonic states. image

The influence of thermal aging on absorption phenomena in cross-linked polyethylene cable insulation

Absorption-controlled charge and discharge currents in cross-linked polyethylene (XPE) cable insulation before and after thermal aging have been measured. The experimental dependences were analyzed in terms of the equivalent Voigt scheme. Known parameters of the Voigt scheme were used to calculate the frequency dependences of relative dielectric permittivity, loss factor, and loss tangent of XPE films in the region of low frequencies (ω = 10–3–1 s–1) at high temperatures. Results of analysis of the absorption characteristics of XPE were applied to modeling of the process of thermal aging of cable insulation.

Untangling the mystery of absorptive capacity: A process or a set of success factors?

The absorptive capacity of an organization is its ability to translate the knowledge sourced from outside into commercial benefits. Having gained a certain academic interest, the mechanism of the absorptive capacity phenomenon is still puzzling. This paper provides some limited confirmation of earlier frameworks; however, absorptive capacity is demonstrated to be a set of interrelated success factors rather than a sequential process of knowledge articulation in a company. The new model of absorptive capacity proposed encompasses four dimensions: continuing development, bottom-up innovation, trust-based internal cooperation, and deferred knowledge use. The continuing development facet entails a strong positive impact on organizational performance, while the bottom-up innovation dimension deteriorates it. Trust-based internal cooperation and deferred knowledge use report mixed results.

Molecular photosensitisers for two-photon photodynamic therapy.

Two-photon excitation has attracted the attention of biologists, especially after the development of two-photon excited microscopy in the nineties. Since then, new applications have rapidly emerged such as the release of biologically active molecules and photodynamic therapy (PDT) using two-photon excitation. PDT, which requires a light-activated drug (photosensitiser), is a clinically approved and minimally invasive treatment for cancer and for non-malignant diseases. This feature article focuses on the engineering of molecular two-photon photosensitisers for PDT, which should bring important benefits to the treatment, increase the treatment penetration depth with near-infrared light excitation, improve the spatial selectivity and reduce the photodamage to healthy tissues. After an overview of the two-photon absorption phenomenon and the methods to evaluate two-photon induced phototoxicity on cell cultures, the different classes of photosensitisers described in the literature are discussed. The two-photon PDT performed with historical one-photon sensitisers are briefly presented, followed by specifically engineered cyclic tetrapyrrole photosensitisers, purely organic photosensitisers and transition metal complexes. Finally, targeted two-photon photosensitisers and theranostic agents that should enhance the selectivity and efficiency of the treatment are discussed.

Modelling of the Water Absorption Kinetics and Determination of the Water Diffusion Coefficient in the Pith ofRaffia viniferaof Bandjoun, Cameroon

The present work focuses on the study of the water absorption phenomenon through the pith ofRaffia viniferaalong the stem. The water absorption kinetics was studied experimentally by the gravimetric method with the discontinuous control of the sampling mass at temperature of 30°C. The samples of 70 mm × 8 mm × 4 mm were taken from twelve sampling zones of the stem ofRaffia vinifera. The result shows that the percentage of water absorption of the pith ofRaffia viniferaincreases from the periphery to the center in the radial position and from the base to the leaves in the longitudinal position. Fick’s second law was adopted for the study of the water diffusion. Eleven models were tested for the modelling of the water absorption kinetics and the model of Sikame Tagne (2014) is the optimal model. The diffusion coefficients of two stages were determined by the solution of the Fick equation in the twelve sampling zones described by Sikame Tagne et al. (2014). The diffusion coefficients decreased from the center to the periphery in the radial position and from the base to the leaves in the longitudinal position.

Diamond graphitization by laser-writing for all-carbon detector applications

The surface of a detector grade CVD polycrystalline diamond sample (5×5×0.05mm3) was irradiated by an ArF excimer laser (λ=193nm, τ=20ns) to produce graphitic conductive layers.In particular, two sets of four parallel graphitic strip-like contacts, with 1mm pitch, were created along the whole sample on the top and on the rear surfaces of the sample respectively. The two series of stripes lie normally to each other. Such a grid allows to obtain a segmented all-carbon device capable of giving bi-dimensional information on particle detection processes in nuclear applications.Afterwards, an extensive characterization of the samples was performed: SEM and micro-Raman investigations to study the morphological and structural evolution of the irradiated areas, EDS measurements to individuate any absorption phenomena from environment associated to laser treatment, and nanoindentation mapping to understand how the hard-soft transformation occurred depending on the locally transferred energy. Finally, current-voltage analyses were carried out checking the ohmic behavior of the diamond-graphite contact. By comparing the results of the different characterization analyses, a strong periodicity of the modified surface properties was found, confirming the reliability and reproducibility of the laser-induced graphitization process.The results demonstrate that the laser-writing technique is a good and fast solution to produce graphitic contacts on diamond surface and therefore represents a promising way to fabricate segmented all-carbon devices.

Laser milling of martensitic stainless steels using spiral trajectories

A laser beam with sub-picosecond pulse duration was driven in spiral trajectories to perform micro-milling of martensitic stainless steel. The geometry of the machined micro-grooves channels was investigated by a specifically conceived Scanning Probe Microscopy instrument and linked to laser parameters by using an experimental approach combining the beam energy distribution profile and the absorption phenomena in the material. Preliminary analysis shows that, despite the numerous parameters involved in the process, layer removal obtained by spiral trajectories, varying the radial overlap, allows for a controllable depth of cut combined to a flattening effect of surface roughness. Combining the developed machining strategy to a feed motion of the work stage, could represent a method to obtain three-dimensional structures with a resolution of few microns, with an areal roughness Sa below 100nm.

First principles study for the key electronic, optical and nonlinear optical properties of novel donor-acceptor chalcones

Using first-principle methods, several key electronic, optical and nonlinear optical properties are calculated for two recently synthesized chalcone derivatives i.e. (2E)-3-(4-methylphenyl)-1-(3-nitrophenyl)prop-2-en-1-one (comp.1) and (2E)-3-[4-(dimethylamino)phenyl]-1-(3-nitrophenyl)prop-2-en-1-one (comp.2). The calculation of dipole moment, polarizability <α>, anisotropy of polarizability as well as second hyperpolarizability (usually considered as a signature for two photon absorption phenomenon) are performed using density functional theory methods at PBE0/6-311G** level of theory. The linear average polarizability <α> for comp.1 and comp.2 are found to be 32.15×10−24 and 38.76×10−24esu, respectively. Similarly, the second hyperpolarizability <γ> amplitudes of comp.1 and comp.2 are found to be reasonably larger mounting to 79.31×10−36 and 181.36×10−36esu, respectively. The importance of donor end is determined by comparing p-methylphenyl group of comp.1 with that of N,N-dimethylaniline group of comp.2 that results a remarkable increase in its <γ> amplitude, which is ∼2 times larger as compared with that of comp.1 owing to the stronger donor-acceptor configuration of comp.2. Interestingly, a comparison of average static third-order nonlinear polarizabilities <γ> shows that <γ> amplitudes of comp.1 and comp.2 are ∼13 times and ∼29 times larger than that of para-nitroaniline (a typical standard push-pull NLO-phore) at the same PBE0/6-311G** level of theory, which indicates a real time NLO application of our titled compounds. Time dependent density functional theory (TD-DFT) calculations along with frontier molecular orbitals, density of states (DOS), second hyperpolarizability density analysis and molecular electrostatic potential (MEP) diagrams are used to trace the origin of electro-optical as well as structure property relationships.

Tunneling induced absorption with competing Nonlinearities.

We investigate tunneling induced nonlinear absorption phenomena in a coupled quantum-dot system. Resonant tunneling causes constructive interference in the nonlinear absorption that leads to an increase of more than an order of magnitude over the maximum absorption in a coupled quantum dot system without tunneling. Resonant tunneling also leads to a narrowing of the linewidth of the absorption peak to a sublinewidth level. Analytical expressions show that the enhanced nonlinear absorption is largely due to the fifth-order nonlinear term. Competition between third- and fifth-order nonlinearities leads to an anomalous dispersion of the total susceptibility.

Donor impurity-related optical absorption coefficients and refractive index changes in a rectangular GaAs quantum dot in the presence of electric field**Project supported by the Science and Technology Project of Education Department of Heilongjiang Province of China (No. 12541070).

Within the quasi-one-dimensional effective potential model and effective mass approximation, we obtain the wavefunctions and energy eigenvalues of the ground (j = 1) and first 2 excited states (j = 2 and 3) of a donor impurity in a rectangular GaAs quantum dot in the presence of electric field. The donor impurity-related linear and nonlinear optical absorption as well as refractive index changes for the transitions j = 1−2 and j = 2−3 are investigated. The results show that the impurity position, incident optical intensity and electric field play important roles in the optical absorption coefficients and refractive index changes. We find that the impurity effect induces the blueshift for j = 1−2 and redshift for j = 3−2 in the absence of the electric field, but it leads to redshift for j = 1−2 and blueshift for j = 3−2 in the existence of the field. Also, the optical coefficient for the higher energy transitions j = 2−3 is insensitive to variation of impurity positions, while that for the low energy transition j = 1−2 depends significantly on the positions of impurity. In addition, the saturation and splitting phenomenon of the optical absorption are observed as the incident optical intensity increases.

Modeling wave propagation through the skull for ultrasonic transcranial Doppler

One problem associated with transcranial Doppler ultrasound (TCD) is the relatively low energy penetrating inside the brain through the skull, seriously limiting the image quality. This may be due to the impedance mismatch at the bone interface and to the bone frequency dependent attenuation. The objective of this paper is to model ultrasonic wave propagation through the skull. To do so, an analytical model was developed based on the estimation of the transmission coefficients inside the brain, leading to frequency dependent overall transmission coefficient for a given skin and bone thickness. Moreover, a finite element model was developed taking into account absorption phenomena. Both methods were validated experimentally by comparing the numerical and analytical results with results obtained from a phantom mimicking the skull having an attenuation coefficient equal to 30 dB/cm at 2.25 MHz and a thickness of 4.4 mm. A 2 mm layer of water mimicked the skin. The difference between the maximum amplitude of normalized received US signals obtained analytically and experimentally was 1%. The average relative difference between them was 0.3%. Thus, a working model is designed which can predict the energy inside the brain. Furthermore, the results show that impedance mismatch plays a major role in transmission loss rather than frequency dependent attenuation

Characterization of absorption and non-linear effects in infrasound propagation using an augmented Burgers’ equation

Abstract The long-range atmospheric propagation of explosion-like waves of frequency in the infrasound range is investigated using non-linear ray theory. Simulations are performed for sources of increasing amplitude on rays up to the lower thermosphere and for distances of hundreds of kilometres. A study of the attenuation of the waveforms observed at ground level induced by both the classical mechanisms and the vibrational relaxation of the molecules comprising the atmospheric gas is carried out. The relative importance of classical absorption and vibrational relaxation along the typical atmospheric propagation trajectories is assessed. Non-linear effects are highlighted as well and particular emphasis is placed on their strong interaction with absorption phenomena. A detailed description of the propagation model and of the numerical algorithm used in this work is first reported. Results are then discussed and the importance of the different mechanisms is clarified.

Simultaneous resolution of the micromagnetic and spin transport equations applied to current-induced domain wall dynamics

In this paper, we use simulations to study current-induced domain wall dynamics by simultaneously resolving the spin transport and micromagnetic equations for a three-dimensional ferromagnetic strip. In contrast to local approaches, which neglect mutual interaction between spins and magnetic moments, our approach recalculates the spin distribution at each time step using the generalized drift diffusion model, which takes the transverse spin absorption phenomenon into account. We quantified the differences between a local approach and treatment based on a self-consistent method by plotting the domain wall velocity as a function of the domain wall width. We also characterized the domain wall velocity and the Walker breakdown condition as a function of the transverse spin absorption length ${l}_{\ensuremath{\perp}}$, which plays a crucial role in domain wall dynamics.

Tunable dual-band nearly perfect absorption based on a compound metallic grating

ABSTRACTTraditional metallic gratings and novel metamaterials are two basic kinds of candidates for perfect absorption. Comparatively speaking, metallic grating is the preferred choice for the same absorption effect because it is structurally simpler and more convenient to fabricate. However, to date, most of the perfect absorption effects achieved based on metamaterials are also available using an metallic grating except the tunable dual(multi)-band perfect absorption. To fill this gap, in this paper, by adding subgrooves on the rear surface as well as inside the grating slits to a free-standing metallic grating, tunable dual-band perfect absorption is also obtained for the first time. The grooves inside the slits is to tune the frequency of the Cavity Mode(CM) resonance which enhances the transmission and suppresses the reflectance simultaneously. The grooves on the rear surface give rise to the phase resonance which not only suppresses the transmission but also reinforces the reflectance depression effect. Thus, when the phase resonance and the frequency tunable CM resonance occur together, transmission and reflection can be suppressed simultaneously, dual-band nearly perfect absorption with tunable frequencies is obtained. To our knowledge, this perfect absorption phenomenon is achieved for the first time in a designed metallic grating structure.

Dynamic micromagnetic simulation of the magnetic spectrum of permalloy nanodot array with vortex state

Due to its potential applications in high-density magnetic storage and spin electronic devices, the ferromagnetic resonance absorption phenomenon has recently drawn much attention. By studying the influence of different materials with various shapes on this phenomenon, the new understandings gained could lead to other applications in the future. In this paper, dynamic magnetic susceptibilities of the vortex state in permalloy nanodot arrays have been investigated using a three-dimensional object oriented micromagnetic framework (OOMMF) code with a two-dimensional periodic boundary condition (2D-PBC) extension and compared with those of a single dot carefully. The resonance mode is excited in the vortex state of nanodot arrays by the microwave magnetic field perpendicular to the dot plane. In this case only radially symmetric spin wave modes can be excited. The influence of the geometric parameters on the resonance frequency has been studied systemically, including the dot radius, the number of repeating elements, and the dot distance. One can see that the resonance peak of the dot array is higher than that of a single dot because of the induced stronger magnetostatic coupling. A critical dot distance exists at which the dot array may be treated as a single dot. There is only one resonance peak for both the dot array and the single dot, as the radius changes.

Modeling bubble evolution in air-oil mixture with a simplified method

This work addresses the problem of bubble evolution arising from gas cavitation in hydraulic oils. Two significant aspects, including the interphase mass transfer represented by air release and absorption phenomena and different thermodynamic considerations, are currently taken into account using a simplified method. In particular, three new models in progressive relationship are proposed on the basis of Rayleigh–Plesset equation which describes bubble dynamics. They are Model A in which air content is assumed to be constant, Model B in which the interphase mass transfer is introduced with the air undergoing an isothermal transformation, and Model C assuming an adiabatic process for the bubble evolution. With the goal of investigating the effects of these aspects, comparisons of the three models for two typical cases are presented with regard to the practical circumstances in which the oil pressure is set to increase linearly or oscillate sinusoidally. Results show a consistent trend for both cases concerning Model B and Model C compared to Model A. Although its speed relates to many factors, air release and absorption has a relevant impact on gas bubble radius. By the reason of adiabatic assumption, Model C provides a slower response regarding the oil pressure change. However, Model B and Model C may be both inaccurate if considering the actual interfacial heat transfer. In this viewpoint, the oil temperature in fluid power system could be affected.

Brain biomarkers for mental disorders: Where are we and how can we be more successful?

The biopharmaceutics classification system (BCS) was based on the tube model of the intestinal lumen. This model considers constant drug permeability along the intestines, a plug flow fluid with the suspended drug particles moving with the fluid, and dissolution in the small particle limit. Since then the research work focusing on drug gastrointestinal (GI) absorption phenomena and processes rely on the classical laws of transport, diffusion and kinetics; however, the homogeneous assumptions associated with the well-stirred Euclidean media, where the classical laws of diffusion and kinetics apply, have been questioned in the past. In this work we explore the biopharmaceutic classification of drugs using a heterogeneous pseudo steady-state model of oral drug absorption. The fraction of dose absorbed (Fabs) was expressed as a function of two time-dependent processes where time dependent coefficients govern drug absorption and non-absorption processes. Fundamental drug properties like the absorption potential are correlated with Fabs and allow the biopharmaceutic classification of drugs taking into account the heterogeneous aspects of oral drug absorption. This analysis reveals that for Class I drugs no time dependency is expected for both absorption and non absorption processes since the gastric emptying is controlling the absorption of Class I drugs while the completion of absorption (Fabs > 90%) is terminated along the first part of the jejunum. Due to the biopharmaceutical properties of Class II, III and IV drugs, these drugs travel throughout the GI tract and therefore both absorption and non absorption processes will exhibit time dependency. Thus, the calculation of Fabs (< 90%) for Class II, III and IV is dependent on the estimates of the time exponents of time dependent coefficients controlling drug absorption e.g. dissolution, uptake or non absorption e.g. precipitation.

Biopharmaceutic classification of drugs revisited

The biopharmaceutics classification system (BCS) was based on the tube model of the intestinal lumen. This model considers constant drug permeability along the intestines, a plug flow fluid with the suspended drug particles moving with the fluid, and dissolution in the small particle limit. Since then the research work focusing on drug gastrointestinal (GI) absorption phenomena and processes rely on the classical laws of transport, diffusion and kinetics; however, the homogeneous assumptions associated with the well-stirred Euclidean media, where the classical laws of diffusion and kinetics apply, have been questioned in the past. In this work we explore the biopharmaceutic classification of drugs using a heterogeneous pseudo steady-state model of oral drug absorption. The fraction of dose absorbed (Fabs) was expressed as a function of two time-dependent processes where time dependent coefficients govern drug absorption and non-absorption processes. Fundamental drug properties like the absorption potential are correlated with Fabs and allow the biopharmaceutic classification of drugs taking into account the heterogeneous aspects of oral drug absorption. This analysis reveals that for Class I drugs no time dependency is expected for both absorption and non absorption processes since the gastric emptying is controlling the absorption of Class I drugs while the completion of absorption (Fabs>90%) is terminated along the first part of the jejunum. Due to the biopharmaceutical properties of Class II, III and IV drugs, these drugs travel throughout the GI tract and therefore both absorption and non absorption processes will exhibit time dependency. Thus, the calculation of Fabs (<90%) for Class II, III and IV is dependent on the estimates of the time exponents of time dependent coefficients controlling drug absorption e.g. dissolution, uptake or non absorption e.g. precipitation.