Microwave Stimulation Research Articles

Experimental investigation and numerical simulation of simultaneous desulfurization and denitrification by H2O2 solution assisted with microwave and additive

Abstract The integrated process for the simultaneous desulfurization and denitrification using H2O2 solution assisted with additive as well as microwave was presented, and researched by chemical dynamics simulations and experiments. The NOx removal process occurred in an atmosphere containing H2O2, OH and HO2 , where the NO was gradually oxidized into HNO3. However, the removal reactions of SO2 in flue gas had some strong competitive relevance with those reactions of NOx. But if with the microwave irradiation, it could tremendously decrease the activation energies of H2O2 decompositions and NOx oxidations with additive. Moreover, the O radical derived from the microwave irradiation could easily enhance the NO decomposition into the N radical, which would also react with the NO to regenerate another O radical, consequently the NO could be reduced into N2 during the conversions among free radicals. By experiments it was found that the denitration efficiency increased first and then decreased with the variations of some factors, such as the temperature, the pH value, the reaction time, the liquid-gas ratio, and the gas volume fractions of O2, NO as well as SO2. Additionally, the NO removal efficiencies presented a monotonous rise law with the increasing concentration of no matter H2O2 or additive. In detail, without the microwave irradiation, more than 99% desulfurization efficiency and 73.4% denitrification efficiency could be achieved at the optimal operating condition. Furthermore, for determining the microwave effects, the removal experiments with microwave stimulation were all performed at pH value of 7, at which the denitration efficiency was the lowest when without microwave irradiation, but now the desulfurization efficiency stabilized above 99.5%, and the denitration efficiency could raise greatly and reach 87.74%.

ZnO capped flower-like porous carbon-Fe3O4 composite as carrier for bi-triggered drug delivery.

In this work, ZnO capped flower-like porous carbon-Fe3O4 composite (FPCS-Fe3O4-ZnO) was constructed as a carrier for pH and microwave bi-triggered drug delivery. In the composite, the FPCS achieves high-efficiency drug loading, the Fe3O4 acts as magnetic targeting agent and microwave absorption enhancer, and the ZnO nanoparticle as a sealing agent in response to pH stimulation. The carrier exhibited a flower-mesoporous sphere of 270 nm, a specific surface area of 101 m2/g, a saturation magnetization of 14.08 emu/g, as well as good microwave thermal conversion properties (The temperature was raised from 25 °C to 60 °C only 24 s). Simultaneously, the carrier achieved an efficient drug loading with a drug loading rate of 99.1%. During the drug release experiments, obvious pH-dependent release behavior was observed, the drug release rate at 12 h was 8.2%, 19.0%, and 56.3% at pH 7.4, 5.0 and 3.0 respectively. Moreover the drug release rate increased from 8.2% to 39.9% after microwave stimulation at pH 7.4. In addition, cytotoxicity tests indicate that the carrier has good biocompatibility. Thus, this multifunctional pH and microwave bi-triggered carrier was expected to be further applied to drug delivery system(DDS).

Microwave stimulation of dislocations and the magnetic control of the earthquake core

Microwave irradiation transforms the elasticity of solids into plasticity by controlling the dislocation mobility via magnetic interactions within the electron spin pairs on the dislocations. In ionic crystals, microwaves cause dislocations to accelerate and increase their mean free path, thus leading to a release of elastic energy; in covalent crystals, microwaves keep dislocations in place, thereby accumulating elastic energy and increasing the crystal strength. Microwave pumping at resonant Zeeman frequencies (in the magnetic resonance regime) is firm evidence of the concepts of electron spin pairs and of the magnetoplasticity phenomenon itself. However, the dominant contribution to the macroscopic transformation of elastic energy into plastic flow comes from nonresonant microwaves. These can be used to control the mechanics of diamagnetic solids, including, importantly, the earthquake focus. The observed correlation between magnetic events (such as magnetic storms and hydrodynamically generated high-power magnetic pulses) and their seismic and tectonic consequences (earthquake frequency and magnitude and deformations) indicates unambiguously that magnetically controlling the earthquake focus provides a realistic means to prevent a catastrophe by transforming large-magnitude earthquakes into weak, low-magnitude events.

Preparation of flower-dewdrops Fe3O4/carbon-SiO2 microsphere for microwave-triggered drug delivery

In this work, the carbon-based microsphere with hollow-nanoflower structure was designed and applied to the targeted drug delivery system (TDDS) in order to improve drug loading and microwave control efficiency. We utilize the “silicon-assisted” method to tailor the hollow mesoporous carbon nanoflower (HMCNF) microspheres as base material, then small Fe3O4 particles (5–12 nm) were precipitated on the HMCNF by thermal decomposition and modified with SiO2 to obtain Fe3O4/HMCNF-SiO2 composites. The tailor-made Fe3O4/HMCNF-SiO2 has unique hollow “flower-dewdrops” structure, large BET surface area (292.21 m2/g) and uniform pore size (5.61 nm) to achieve large storage of drugs. Meanwhile, the Fe3O4/HMCNF-SiO2 has the appropriate magnetic properties (Ms = 8.91 emu/g) and good microwave heat transfer performance, which can achieve the drug carrier targeting and microwave-triggered release. Furthermore, the Fe3O4/HMCNF-SiO2 has a higher drug loading rate of 70.20% (DOX loading of 175.50 mg/g) and an expected release behavior. It maintains a very low drug release rate only 1.5% at pH = 7.4 and then increased to 25.2% after microwave stimulation at pH = 5.0. Therefore the Fe3O4/HMCNF-SiO2 composite nanocarrier is expected to widely use in microwave-triggered drug delivery system.

Микроволновoе стимулирование дислокаций и магнитный контроль очага землетрясения

Микроволновoе стимулирование дислокаций и магнитный контроль очага землетрясения

Thermally Driven Inhibition of Superconducting Vortex Avalanches

Complex systems close to their critical state can exhibit abrupt transitions, avalanches, between their metastable states. It is a challenging task to understand the mechanism of the avalanches and control their behavior. Here we investigate microwave (mw) stimulation of avalanches in the so- called vortex matter of type II superconductors, a system of interacting Abrikosov vortices close to the critical (Bean) state. Our main finding is that the avalanche incubation strongly depends on the excitation frequency, a completely unexpected behavior observed close to the so-called depinning frequencies. Namely, the triggered vortex avalanches in Pb superconducting films become effectively inhibited approaching the critical temperature or critical magnetic field when the mw stimulus is close to the vortex depinning frequency. We suggest a simple model explaining the observed counter- intuitive behaviors as a manifestation of the strongly nonlinear dependence of the driven vortex core size on the mw excitation intensity. This paves the way to controlling avalanches in complex systems through their nonlinear response.

Nanophotosensitive drugs for light-based cancer therapy: what does the future hold?

Nanophotosensitive drugs for light-based cancer therapy: what does the future hold?

Investigations of microwave stimulation of a turbulent low-swirl flame

Irradiating a flame by microwave radiation is one of several plasma-assisted combustion (PAC) technologies that can be used to modify the combustion chemical kinetics in order to improve flame-stability and to delay lean blow-out. One practical implication is that engines may be able to operate with leaner fuel mixtures and have an improved fuel flexibility capability including biofuels. In addition, this technology may assist in reducing thermoacoustic instabilities that may severely damage the engine and increase emission production. To examine microwave-assisted combustion a combined experimental and computational study of microwave-assisted combustion is performed for a lean, turbulent, swirl-stabilized, stratified flame at atmospheric conditions. The objectives are to demonstrate that the technology increases both the laminar and turbulent flame speeds, and modifies the chemical kinetics, enhancing the flame-stability at lean mixtures. The study combines experimental investigations using hydroxyl (OH) and formaldehyde (CH2O) Planar Laser-Induced Fluorescence (PLIF) and numerical simulations using finite rate chemistry Large Eddy Simulations (LES). The reaction mechanism is based on a methane (CH4)–air skeletal mechanism expanded with sub-mechanisms for ozone, singlet oxygen, chemionization, electron impact dissociation, ionization and attachment. The experimental and computational results show similar trends, and are used to demonstrate and explain some significant aspects of microwave-enhanced combustion. Both simulation and experimental studies are performed close to lean blow off conditions. In the simulations, the flame is gradually subjected to increasing reduced electric field strengths, resulting in a wider flame that stabilizes nearer to the burner nozzle. Experiments are performed at two equivalence ratios, where the leaner case absorbs up to more than 5% of the total flame power. Data from experiments reveal trends similar to simulated results with increased microwave absorption.

Setup for microwave stimulation of a turbulent low-swirl flame

An experimental setup for microwave stimulation of a turbulent flame is presented. A low-swirl flame is being exposed to continuous microwave irradiation inside an aluminum cavity. The cavity is designed with inlets for laser beams and a viewport for optical access. The aluminum cavity is operated as a resonator where the microwave mode pattern is matched to the position of the flame. Two metal meshes are working as endplates in the resonator, one at the bottom and the other at the top. The lower mesh is located right above the burner nozzle so that the low-swirl flame is able to freely propagate inside the cylinder cavity geometry whereas the upper metal mesh can be tuned to achieve good overlap between the microwave mode pattern and the flame volume. The flow is characterized for operating conditions without microwave irradiation using particle imaging velocimetry (PIV). Microwave absorption is simultaneously monitored with experimental investigations of the flame in terms of exhaust gas temperature, flame chemiluminescence (CL) analysis as well as simultaneous planar laser-induced fluorescence (PLIF) measurements of formaldehyde (CH2O) and hydroxyl radicals (OH). Results are presented for experiments conducted in two different regimes of microwave power. In the high-energy regime the microwave field is strong enough to cause a breakdown in the flame. The breakdown spark develops into a swirl-stabilized plasma due to the continuous microwave stimulation. In the low-energy regime, which is below plasma formation, the flame becomes larger and more stable and it moves upstream closer to the burner nozzle when microwaves are absorbed by the flame. As a result of a larger flame the exhaust gas temperature, flame CL and OH PLIF signals are increased as microwave energy is absorbed by the flame.

Simulation of microwave stimulation for the production of gas from methane hydrate sediment

Natural gas hydrates dissociate via an endothermic process. One of the key requirements for any production technique is to supply the heat necessary for this dissociation. In this study, first, a microwave stimulation model for the production of gas from methane hydrate sediment is developed, which includes mass transport, energy conversion and conservation, and intrinsic kinetic reactions as the governing equations. In addition, the theoretical mixing rule of Lichtenecker and Rother is introduced for calculating the average dielectric data of the sediment containing methane hydrates, which affects the penetration of microwaves into the sediment. Next, simulations are performed for investigating gas production, as well as effects of initial water saturation, initial hydrate saturation, and sediment thermal properties induced by microwave stimulation. Moreover, the energy efficiency ratio is employed in the simulation. The simulation results show that microwave stimulation provides timely energy conversion sufficient for promoting the dissociation of hydrates, with rapid, continuous gas production. Temperature gradients caused by the decrease of the microwave penetration depth appear in the reservoir, leading to a rapid dissociation rate in the upper part of the sediment. The energy efficiency ratio for all simulations ranges between 3.752 and 6.452. Hydrate saturation and the specific heat capacity of porous media are two factors that significantly affect energy efficiency. High hydrate saturation contributes to a rapid gas generation rate and a long rapid gas generation lasting time, leading to a high energy efficiency. A low specific heat capacity of porous media can decrease the loss of heat to the sediment, increase the gas generation rate, and improve energy efficiency. Furthermore, high initial water saturation can cause a rapid decrease in the microwave penetration depth and lead to large temperature gradients in the sediment. The thermal conductivity of porous media mainly affects gas generation in the latter period of hydrate dissociation. Macroscopic heat conduction in the sediment decreases the temperature gradients in the reservoir and promotes homogeneous hydrate dissociation.

A novel stimulation: Tailoring conductivity transition in Gd1−xCaxBaCo2O5+δ (x=0–0.4) by microwave stimulation

Control of the insulator–metal transition (IMT) is a constant focus of intensive study, owing to its importance to the exploration of novel effects and in Information Technology. Complex oxides with competitive mechanisms are suitable objects of study in this regard, because of their susceptibility to external stimuli. The double-perovskite cobaltate Gd1−xCaxBaCo2O5+δ (GCBC) is one such oxide. In this paper, the combined effects of the GCBC structure and Ca2+ doping have been studied for 0≤x≤0.4, which offers the possibility of systemic modulation of the conductivity (σ) of the GCBC via microwave stimulation. The maximum value and rate of increase of σ increase with the microwave power, and it has been found that the conductivity of Gd0.8Ca0.2BaCo2O5+δ can increase from 158 to 1488S/cm at a frequency of 2.45GHz (1500W) over 2min. Thus, our experimental study confirms that microwaves are crucial for controlling the electrical properties of cobaltates.

Microwave assisted chemistry: A rapid and regioselective route for direct ortho-acylation of phenols and naphthols by methanesulfonic acid as catalyst

Direct ortho-acylation of phenols and naphthols with methanesulfonic acid (MSA) as the catalyst has been studied under microwave stimulation. The microwave assisted reaction was environmentally benign in terms of faster reaction, useful conditions and higher yield of the desired products. However, after 3–4min reaction time at 200–300Watt, selectivity to over 98% ortho-acylation products was obtained. These reactions have some advantages in competition with other methods such as; short reaction times, high yield and regioselectivity of products, mild reaction conditions and easy workup of the reactions.

Facile non-hydrolytic synthesis of highly water dispersible, surfactant free nanoparticles of synthetic MFe2O4 (M–Mn2+, Fe2+, Co2+, Ni2+) ferrite spinel by a modified Bradley reaction

A series of the highly crystalline MFe2O4 ferrite spinel nanoparticles were synthesized via a modified Bradley reaction using microwave stimulation. Particle size was estimated using theoretical calculations from the X-ray data (Scherrer and Rietveld methods) as well as by direct experimental techniques such as TEM, DLS and NTA. The calculated average grain size for dry powders is in the range 10 to 23 nm. Hydrodynamic size was measured using DLS on non-modified, surfactant free particles of the whole MFe2O4 series. Raman spectra used for additional verification of the structure features of the produced spinel phases showed strong asymmetric behavior of the A1g mode, which was deconvoluted revealing additional components. Among all the products the lowest site inversion was found for the manganese ferrite (MnFe2O4). The oxidation of Fe3O4 leading to the formation of the Fe2O3 hematite phase induced by laser irradiation was observed. Magnetic characterization of the MFe2O4 family was carried out, showing that superparamagnetic blocking temperatures and calculated anisotropy constants K are in good agreement with the data for similar fine-particle systems.

Experimental Investigation on the Dissociation Behavior of Methane Gas Hydrate in an Unconsolidated Sediment by Microwave Stimulation

The technique of recovery of methane from a hydrate reservoir by microwave stimulation was experimentally verified for a laboratory scale. The stimulation was carried out in the unconsolidated sedi...

Microwave stimulation of plasticity in an earthquake source

It is suggested to stimulate the slow relaxation of elastic energy of deformation stress in an earth-quake source by microwave radiation, which intensifies the motion of dislocations, decreases the yield limit, and increases the plasticity. This phenomenon, known in solid-state physics as magnetoplasticity, can be used to retain an earthquake source far from the critical regime capable of developing into a catastrophic earth-quake by stimulating a slow relaxation of the source. The available evidence for the influence of magnetic storms on the dynamics of earthquakes is generally consistent with the concept of stimulated magnetoplasticity as a means of preventing catastrophic earthquakes, proposed in the present communication.

Multifrequency Microwave-Induced Thermal Acoustic Imaging for Breast Cancer Detection

Microwave-induced thermal acoustic imaging (TAI) is a promising early breast cancer detection technique, which combines the advantages of microwave stimulation and ultrasound imaging and offers a high imaging contrast, as well as high spatial resolution at the same time. A new multifrequency microwave-induced thermal acoustic imaging scheme for early breast cancer detection is proposed in this paper. Significantly more information about the human breast can be gathered using multiple frequency microwave stimulation. A multifrequency adaptive and robust technique (MART) is presented for image formation. Due to its data-adaptive nature, MART can achieve better resolution and better interference rejection capability than its data-independent counterparts, such as the delay-and-sum method. The effectiveness of this procedure is shown by several numerical examples based on 2-D breast models. The finite-difference time-domain method is used to simulate the electromagnetic field distribution, the absorbed microwave energy density, and the thermal acoustic field in the breast model.

Friedel-Crafts acylation reactions using heterogeneous catalysts stimulated by conventional and microwave heating

The acylation of anisole with decanoic acid over a range of solid-acid catalysts has been studied under conventional heating and microwave stimulation. The microwave-irradiated experiments exhibited increased reaction rates, the extent of which was dependent upon the nature of the catalyst. The origin of this microwave enhancement has been attributed to the selective desorption of water from the surface of the catalyst. Pyridine adsorption has been used to quantify the number of acid sites present on the catalyst. The nature of the acid sites in terms of their Brønsted/Lewis acidity has been determined using infrared analysis of the adsorbed pyridine. The strength of the acid sites has been characterised by differential thermal analysis (DTA) of the pyridine desorption. This indicated that the sulphated zirconia and supported heteropoly acids contained significantly more strong acid sites than the cerium exchanged zeolite.

Non-Thermal Effect of Microwave Radiation on Human Brain

This study focuses on an origin of interaction mechanism of microwave radiation with nervous system—quasi-thermal field effect. The microwave field can cause fluctuations and vibration of the charged particles and membranes in tissues. The hypothesis is, that this phenomenon is similar to the effect caused by Brown motion initiated by temperature and results in the same effects without rise in temperature. The electric field of 1 V/cm can introduce disturbance of the thermal equilibrium inside a cell of 10 μm radius, which is equivalent to disturbance produced by temperature rise of 1 K. The hypothesis, that microwave heating should cause an effect independent of the microwave modulation frequency, while field effect depends on modulation frequency, was examined experimentally. The 450 MHz microwave radiation, modulated at 7, 14 and 21 Hz frequencies, power density at the skin 0.16 mW/cm2, was applied. The experimental protocol consisted of two series of five cycles of the repetitive microwave exposure at fixed modulation frequencies. Relative changes in EEG theta, alpha and beta rhythms of the group of 13 healthy volunteers were analysed. Analysis of the experimental data shows that: (1) statistically significant changes in EEG rhythms depend on modulation frequency of the microwave field; (2) microwave stimulation causes an increase of the EEG energy level; (3) the effect is most intense at beta1 rhythm and higher modulation frequencies. These findings confirm the quasi-thermal origin of the effect, different from average heating.

전기영동법(Electrophoresis)을 이용한 봉약침의 주요 성분에 관한 연구

This study was designed to study on major components of various Bee Venom(Bee Venom by electrical stimulation in Korea; K-BV I, Bee Venom by Microwave stimulation in Korea; K -BV II, 0.5rng/ml, Fu Yu Pharmaceutical Factory, China; C-BV, 1mg /ml, Monmouth Pain Institute, Inc., U.S.A.; A-BV) using Electrophoresis. The results were summarized as follows: 1. In 1:4000 Bee Venom solution rate, the band was not displayed distinctly usmg Electrophoresis. But in 1: 1000, the band showed clearly. 2. The results of Electrophoresis at solution rate 1:1000, K-BV I and K-BVII showed similar band. 3. The molecular weight of Phospholipase was known as 19,000 but its band was seen at 17,000 in Electrophoresis. 4. Protein concentration of Bee Venom by Lowry method was different at solution rate 1:4000 ; C-BV was . Electrophoresis method was unuseful for analysis of Bee Venom when solution rate is above 1:4000 but Protein concentration of Bee Venom by Lowry method was possible. These data from the study can be applied to establish the standard measurement of Bee Venom and prevent pure bee venom from mixing of another components. I think it is desirable to study more about safety of Bee Venom as time goes by.

Hyperfine population measurement of excited OH from $\rm H_2O$ photodissociation by microwave stimulation – first results

In this paper the rst measurement of the hy- perne population of a photofragment is presented. The population of the hyperne levels of the 2 3=2(J =7 =2) state of OH out of photodissociation of cold H2O turns out to be statistical. After photodissociation of water at 157 nm within a Fabry-Perot microwave cavity the nascent OH formed in the v =0 , J =7 =2 state (probed by LIF) is stimulated by microwave radiation. From saturation data the population in each hyperne level in both -doublets is determined.