Absence Of Microwaves Research Articles

Volumetric incorporation of NV diamond emitters in nanostructured F2 glass magneto-optical fiber probes

Integration of optically active diamond particles with glass fibers is a powerful method of scaling diamond's magnetic sensing functionality. We propose a novel approach for the integration of diamond particles containing nitrogen-vacancy centers directly into the fiber core. The core is fabricated by stacking the preform from 790 soft glass canes, drawn from a single rod dip-coated with submicron diamond particles suspended in isopropyl alcohol. This enables manual control over the distribution of nanoscale features, here – the diamond particles across the optical fiber core. We verify this by mapping the diamond distribution in the core using confocal microscopy. The particles are separated longitudinally by 12–29 μm, while in the transverse plane a separation of approximately 1.5–2.2 μm is observed, corresponding to the individual cane diameter in the final fiber, and without significant agglomeration. The fiber's magnetic sensitivity is confirmed in optically detected magnetic resonance recorded with a coiled, 60-cm-long fiber sample with readout contrast of 1.3% limited by microwave antenna coverage. Moreover, magnetic-field dependence of the NV─ fluorescence intensity is demonstrated in the absence of microwaves, allowing magnetometric applications with a large (from 0 to 35 mT) B-field dynamic range.

Microwave-Assisted Hydrogen-Free Reductive Deiodination of Iodoarenes with Silicon-Nanoarray Palladium-Nanoparticle Catalyst

AbstractThe hydrogenolysis of iodoarenes using a silicon nanoarray palladium catalyst under microwave irradiation was investigated. When triethanolamine was used as the sacrificial reductant, the reaction proceeded via reductive deiodination under an aerobic atmosphere even without the presence of the explosive hydrogen gas, affording the corresponding hydrogen-substituted arenes in high yields. No reaction occurred in the absence of microwaves, indicating a noticeable microwave effect.

Ablation of cells in mice using antibody-functionalized multiwalled carbon nanotubes (Ab-MWCNTs) in combination with microwaves

This is a proof-of-principle study on the combination of microwaves and multiwalled carbon nanotubes to induce in vivo, localized hyperthermic ablation of cells as a potential methodology for the treatment of localized tumors. Compared to conventional methods, the proposed approach can create higher temperatures in a rapid and localized fashion, under low radiation levels, eliminating some of the unwanted side effects. Following successful ablation of cancer cells in cell culture and zebrafish tumor-xenograft models, it is hypothesized that a cancer treatment can be developed using safe microwave irradiation for selective ablation of tumor cells in vivo using carbon nanotube-Antibody (CNT-Ab) conjugates as a targeting agent. In this study, mice were used as an animal model for the optimization of the proposed microwave treatment strategy. The safe dose of CNT-Ab and microwave radiation levels for mice were determined. Further, CNT-Ab distribution and toxicology in mice were qualitatively determined for a time span of two weeks following microwave hyperthermia. The results indicate no toxicity associated with the CNT-Ab in the absence of microwaves. CNTs are only found in the proximity of the site of injection and have been shown to effectively cause hyperthermia induced necrosis upon exposure to microwaves with no noticeable damage to other tissues that are not in direct contact with the CNT-Ab. To understand the cellular immune response towards CNT-Abs, transgenic zebrafish with fluorescently labeled macrophages and neutrophils were used to assay for their ability to phagocytize CNT-Ab. Our results indicate that macrophages and neutrophils were able to actively phagocytose CNT-Abs shortly after injection. Taken together, this is the first study to show that CNTs can be used in combination with microwaves to cause targeted ablation of cells in mice without any side effects, which would be ideal for cancer therapies.

Sensitivity analysis of magic angle spinning dynamic nuclear polarization below 6 K.

Dynamic nuclear polarization (DNP) improves signal-to-noise in nuclear magnetic resonance (NMR) spectroscopy. Signal-to-noise in NMR can be further improved with cryogenic sample cooling. Whereas MAS DNP is commonly performed between 25 and 110 K, sample temperatures below 6 K lead to further improvements in sensitivity. Here, we demonstrate that solid effect MAS DNP experiments at 6 K, using trityl, yield 3.2× more sensitivity compared to 90 K. Trityl with solid effect DNP at 6 K yields substantially more signal to noise than biradicals and cross effect DNP. We also characterize cross effect DNP with AMUPol and TEMTriPol-1 biradicals for DNP magic angle spinning at temperatures below 6 K and 7 Tesla. DNP enhancements determined from microwave on/off intensities are 253 from AMUPol and 49 from TEMTriPol-1. The higher thermal Boltzmann polarization at 6 K compared to 298 K, combined with these enhancements, should result in 10,000× signal gain for AMUPol and 2000× gain for TEMTriPol-1. However, we show that AMUPol reduces signal in the absence of microwaves by 90% compared to 41% by TEMTriPol-1 at 7 Tesla as the result of depolarization and other detrimental paramagnetic effects. AMUPol still yields the highest signal-to-noise improvement per unit time between the cross effect radicals due to faster polarization buildup (T1DNP = 4.3 s and 36 s for AMUPol and TEMTriPol-1, respectively). Overall, AMUPol results in 2.5× better sensitivity compared to TEMTriPol-1 in MAS DNP experiments performed below 6 K at 7 T. Trityl provides 6.0× more sensitivity than TEMTriPol-1 and 1.9× more than AMUPol at 6 K, thus yielding the greatest signal-to-noise per unit time among all three radicals. A DNP enhancement profile of TEMTriPol-1 recorded with a frequency-tunable custom-built gyrotron oscillator operating at 198 GHz is also included. It is determined that at 7 T below 6 K a microwave power level of 0.6 W incident on the sample is sufficient to saturate the cross effect mechanism using TEMTriPol-1, yet increasing the power level up to 5 W results in higher improvements in DNP sensitivity with AMUPol. These results indicate MAS DNP below 6 K will play a prominent role in ultra-sensitive NMR spectroscopy in the future.

Optimized microwave extraction, characterization and antioxidant capacity of biological polysaccharides from Eucommia ulmoides Oliver leaf

Microwave-induced technique was combined with response surface methodology for optimizing the isolation of polysaccharides from Eucommia ulmoides Oliver leaf. The maximum polysaccharides yield of 12.31% was achieved by microwave extraction at 74 °C for 15 min with a solid to liquid ratio of 1:29 g/mL, which agreed with the predicted value and was 2.9-fold higher than that of the conventional heat-reflux extraction method. The dominant bioactive constituent in extracts was chlorogenic acid (1.3–1.9%), followed by geniposidic acid (1.0–1.7%). The polysaccharides from the optimized extraction had a high molecular weight and polydispersity (Mw 38,830 g/mol, Mw/Mn 2.19), as compared to the fraction prepared in the absence of microwave (Mw 12,055 g/mol, Mw/Mn 1.26). Glucose was the dominant sugar component (38.2–39.1%) of heterogeneous polysaccharides which belonged to a structure of β-type acidic heteropolysaccharides with a glucan group and highly branched degree. The polysaccharides showed a higher DPPH radical scavenging index (0.87–1.22) than BHT (0.41) but lower than BHA (3.56), which can act as a favorable antioxidant in functional food.

Continuous-Flow Microliter Microwave Irradiation in the Synthesis of Isoxazole Derivatives: An Optimization Procedure

An efficient method was developed for the synthesis of 3,4,5-trisubstituted and 3,5-disubstituted isoxazoles by using continuous-flow microwave-heated microreactors. A study on the separate effects of the temperature, continuous-flow regime, and microwave irradiation showed that the continuous-flow regime had important effects for less reactive diketones, where microwave heating enhanced the reaction, permitting the formation of 5-methyl-3-phenylisoxazole, which was not formed in the absence of microwaves.

Microwave-induced magnetoresistance of two-dimensional electrons interacting with acoustic phonons

The influence of electron-phonon interaction on magnetotransport in two-dimensional electron systems under microwave irradiation is studied theoretically. Apart from the phonon-induced resistance oscillations which exist in the absence of microwaves, the magnetoresistance of irradiated samples contains oscillating contributions due to electron scattering on both impurities and acoustic phonons. The contributions due to electron-phonon scattering are described as a result of the interference of phonon-induced and microwave-induced resistance oscillations. In addition, microwave heating of electrons leads to a special kind of phonon-induced oscillations. The relative strength of different contributions and their dependence on parameters are discussed. The interplay of numerous oscillating contributions suggests a peculiar magnetoresistance picture in high-mobility layers at the temperatures when electron-phonon scattering becomes important.

Deep-well ultrafast manipulation of a SQUID flux qubit

Superconducting devices based on the Josephson effect are effectively used for the implementation of qubits and quantum gates. The manipulation of superconducting qubits is generally performed by using microwave pulses with frequencies from 5 to 15 GHz, obtaining a typical operating frequency from 100 MHz to 1 GHz. A manipulation based on simple pulses in the absence of microwaves is also possible. In our system, a magnetic flux pulse modifies the potential of a double SQUID qubit from a symmetric double well to a single deep-well condition. By using this scheme with a Nb/AlOx/Nb system, we obtained coherent oscillations with sub-nanosecond period (tunable from 50 to 200 ps), very fast with respect to other manipulating procedures, and with a coherence time up to 10 ns, of the order of that obtained with similar devices and technologies but using microwave manipulation. We introduce ultrafast manipulation, presenting experimental results, new issues related to this approach (such as the use of a compensation procedure for canceling the effect of ‘slow’ fluctuations) and open perspectives, such as the possible use of RSFQ logic for qubit control.

Melting of Two-Dimensional Electron Crystal on Liquid 3He Induced by Resonance Microwave Absorption

AbstractMicrowave-resonance induced increase of magneto-resistivity σ xx −1 of the surface-state electrons (SSE) on liquid 3He is observed at low temperatures at which SSE crystallize into the Wigner solid (WS). At the resonance, the relative change of σ xx −1 of SSE in the solid phase is found to be several times of the corresponding change in the liquid phase measured under similar experimental conditions. We attribute this effect to melting of WS induced by electron heating which accompanies the microwave absorption. σ xx −1 is found to increase gradually with microwave power, which is rather different from the sharp resistivity increase induced by direct heating of the substrate in the absence of microwaves. The effect of microwave resonance-induced heating on the sliding of WS from the periodic surface deformation of liquid is also investigated.

Microwave Activation of Processes in Mesopores: The Thiourea Electrooxidation at Mesoporous Platinum

AbstractIn situ microwave activation is applied to the electrochemical oxidation of thiourea at low surface area (polished polycrystalline) and at high surface area (electrodeposited mesoporous platinum coated) platinum microelectrodes. The one electron oxidation of thiourea to formamidine disulfide is monitored as a function of the different activation parameters. In the absence of microwaves (ambient temperature, low mass transport) increasing the surface area (roughness) increases the thiourea oxidation response predominantly due to adsorption effects. In the presence of high microwave intensities, high mass transport and thermal effects further increase the oxidation current at mesoporous platinum. The most effective thickness of the mesoporous platinum film for the thiourea oxidation process is estimated as 3 μm independent of electrode diameter, temperature, or mass transport effects.

Microwave-enhanced electrochemical processes in micellar surfactant media

High intensity microwave radiation effects are demonstrated for electron transfer processes at 25 or 50-μm diameter platinum electrodes immersed in micellar sodium dodecylsulfate (SDS) solutions. First, a solution containing 2 mM Fe(CN)63− and 2 mM Fe(CN)64− in aqueous 0.1 M NaCl with and without SDS is employed to calibrate the electrode temperature and mass transport conditions. Addition of 0.1 M SDS has only a small effect on the microwave enhanced voltammetry for the Fe(CN)63-/4− system. Next, two highly water-insoluble redox systems are studied. A solution of 1 mM tert-butylferrocene in aqueous 0.1 M NaCl containing 0.1 M SDS is shown to give no current response in the absence of microwaves. In the presence of focused microwaves at a platinum disc electrode, a strong current for the one electron oxidation of tert-butylferrocene is detected presumably due to localized disruption of the micellar solution. Concentrations of tert-butylferrocene down to the micromolar level are detected. α-Tocopherol, a lipophilic vitamin and antioxidant, is soluble in aqueous 0.1 M SDS/0.1 M NaCl. In the presence of microwave radiation, a strong and concentration dependent anodic current response consistent with the two-electron oxidation of α-tocopherol is observed. A heptode array of seven individual 50 μm diameter platinum microelectrodes placed in ca. 720 μm distance of each other is shown to allow microwave enhanced currents to be increased sevenfold with each electrode exhibiting the same microwave effect.

Desolvating the sample aerosol with microwave radiation: further theoretical and experimental insight into the significance of such approach

This study aims to determine the feasibility of using microwave energy to achieve significant improvements in sample introduction by desolvating a sample aerosol. The efficiency and mechanism of microwave desolvation were investigated. Evidence for significant interaction between aqueous droplets and microwave energy was evaluated by experimental and theoretical methods. A microwave desolvation system incorporating a Nafion dryer was evaluated for ICP-MS. A small improvement in transport to the plasma (between 51 and 60%) was observed for magnesium, lead, and rhodium with 100% microwave power. The mechanism of desolvation was investigated using a different microwave system connected to a flame spectrometer. This system was heated, and sample introduced in the presence of a microwave field and in the absence of microwaves. No significant difference between the two cases was found indicating that the primary mechanism for increased sample transport was conductive heating of the droplets. A numerical model was developed and showed that small droplets (5 μm) are incapable of absorbing sufficient energy from a 2.45 GHz field to heat significantly due to very small absorption efficiencies as predicted by Mie theory calculations.

Vulcanization of rubber mixtures by simultaneous electron beam and microwave irradiation

The comparative results obtained by applying separate electron beam (EB) irradiation and simultaneous EB and microwave (MW) irradiation to vulcanization of rubber mixtures based on natural rubber and polybutadiene rubber with carbon black are presented. In the absence of MW, EB irradiation doses of 200–250 kGy are required in order to obtain a higher vulcanization degree. The irradiation doses as well as irradiation times were markedly diminished, from 2 to 6 times, by simultaneous EB and MW irradiation.

The effect of focused microwaves on the reaction of ethyl N-trichloroethylidenecarbamate with pyrazole derivatives

Under microwave irradiation vinylpyrazoles react with ethyl N-trichloroethylidenecarbamate 1 to give the addition to the imine system through the conjugated vinyl group. Likewise, compound 1 react with the NH group of pyrazolylhydrazones, if present. To the best of our knowledge this reaction type has not been described before and only can be performed under microwave irradiation. By classical heating, in the absence of microwaves, only dimerization or decomposition of the pyrazole derivatives is observed in these reactions.

Can Microwave Ovens Reduce Immunocytochemical Labeling Times?

In recent years the use of microwave ovens in biomedical microscopy laboratories has contributed to reducing the times of fixation and resin embedding. Reports of the use of microwaves for histochemsitry and immunocytochemistry led us to investigate the possible use of a microwave oven to reduce immunocytochemical labeling protocols.The application of specific antibodies to thawed cryosections of aldehyde-fixed material is becoming more accessible to research and service laboratories. These detection methods, routinely performed in our laboratory, were used to study the effect of microwaves on labeling protocols using affinity purified, polyclonal antibodies and protein A-gold.Cells containing 3-(2,4-dinitroanilino)-3-arnino-N-methyldipropylamine (DAMP), a compound which accumulates in low pH compartments, were aldehyde-fixed, cryosectioned and then labeled with rabbit antibodies to dinitrophenol (which bind to DAMP) and 10nm protein-A gold. Regular sequential labeling protocols were compared with protocols using a microwave oven operating at 100% power, where the antibody incubation and washing times were reduced. The effect of microwaves on the labeling efficiency was investigated using simple quantitative methods. The protocol which produced reduced incubation times with no loss of labeling efficiency was then applied to sections in the absence of microwaves. The effect of reducing the final methyl cellulose-uranyl acetate contrasting step was also investigated.

No nonthermal effect observed under microwave irradiation of spinal cord

Presents an in vivo experiment concerning cerebral evoked potentials in the presence and in the absence of microwaves irradiating the spinal cord. An electrical stimulus is applied on the peripheral nervous system of a rabbit while the impulse response (evoked potential) is measured by an electrode in the cortex. The spinal cord is irradiated at 4.2-GHz by an implanted micro-antenna. The purpose of the experiment is to distinguish between thermal and possible nonthermal effects. A statistical treatment of the recorded data shows that there is a microwave effect. Power deposition is calculated. The bioheat equation indicates that the microwave irradiation results in a temperature increase within the spinal cord. Nonthermal effects were not observed.

Radiative Rydberg-atom-Rydberg-atom collisions in the strong-field regime.

We describe the experimental observation of the resonant collisional energy transfer Na(ns)+Na(ns)+qh\ensuremath{\nu}\ensuremath{\rightarrow}Na(np)+Na[(n-1)p]+(q○)h\ensuremath{\nu} which occurs when the Na atoms in a strong microwave field are tuned in energy with a static field so that the energy resonance ${E}_{\mathrm{ns}}$+${E}_{\mathrm{ns}}$=${E}_{\mathrm{np}}$+${E}_{n\mathrm{\ensuremath{-}}1}$,p\ifmmode\pm\else\textpm\fi{}mh\ensuremath{\nu} occurs. We describe our experimental observations and provide a detailed description of a nonperturbative theory which we have developed to explain our observations. The theory is essentially developed in terms of the resonant dipole-dipole collisions between ``microwave dressed'' atoms. Using an extension of the approach we used previously to describe resonant dipole-dipole collisions in the absence of microwaves, we are able to take into account all the coherences in the problem in a completely straightforward way.

Thermoregulatory responses of the immature rat following repeated postnatal exposures to 2,450-MHz microwaves.

This study was designed to determine the changes that occur in the thermoregulatory ability of the immature rat repeatedly exposed to low-level microwave radiation. Beginning at 6-7 days of age, previously untreated rats were exposed to 2,450-MHz continuous-wave microwaves at a power density of 5 mW/cm2 for 10 days (4 h/day). Microwave and sham (control) exposures were conducted at ambient temperatures (Ta) which represent different levels of cold stress for the immature rat (ie, "exposure" Ta = 20 and 30 degrees C). Physiological tests were conducted at 5-6 and 16-17 days of age, in the absence of microwaves, to determine pre- and postexposure responses, respectively. Measurements of metabolic rate, colonic temperature, and tail skin temperature were made at "test" Ta = 25.0, 30.0, 32.5, and 35.0 degrees C. Mean growth rates were lower for rats exposed to Ta = 20 degrees C than for those exposed to Ta = 30 degrees C, but microwave exposure exerted no effect at either exposure Ta. Metabolic rates and body temperatures of all exposure groups were similar to values for untreated animals at test Ta of 32.5 degrees C and 35.0 degrees C. Colonic temperatures of rats repeatedly exposed to sham or microwave conditions at exposure Ta = 20 degrees C or to sham conditions at exposure Ta = 30 degrees C were approximately 1 degrees C below the level for untreated animals at test Ta of 25.0 degrees C and 30.0 degrees C. However, when the exposure Ta was warmer, rats exhibited a higher colonic temperature at these cold test Ta, indicating that the effectiveness of low-level microwave treatment to alter thermoregulatory responses depends on the magnitude of the cold stress.

Detection of Microwave Heating in 5-Hydroxytryptamine-Induced Hypothermic Mice

The intraperitoneal injection of 5-hydroxytryptamine (5-HT) in unrestrained and unanesthetized mice held at 22°C causes a hypothermia which is maximal after approximately 15 min. When mice injected with 5-HT were held in a controlled environment of 22°C and 50% relative humidity and exposed to microwaves (2450 MHz, cw) at $1 {\rm mW}/{\rm cm}^{2}$ for 15 min, significant significant increases were observed in the body temperature of these mice compared to 5-HT-treated sham-irradiated mice. The magnitude of the response was related to power density ( $10>5>1 {\rm mW}/{\rm cm}^{2}$ ). Saline-injected mice exposed for 15 min at 10 mW/ cm2 (specific absorption rate = 7.2 m W/g) showed no significant increase in body temperature compared to saline-injected sham-irradiated mice. The hypothermia induced by 5-HT in mice was also found to be affected by ambient temperature alone. Increases in ambient temperature above 22°C, in the absence of microwaves, caused a concomitant incr...

Josephson effects in Nb<inf>3</inf>Sn microbridges

We have studied Josephson effects in long narrow Nb 3 Sn microbridges at temperatures up to 17 K. These microbridges are formed by photolithographic techniques and subsequently subjected to controlled electrical discharges to modify the intrinsic T c of the bridge region. The bridges exhibit 10 GHz micro wave steps in their I-V characteristics whose amplitudes are in excellent agreement with the Resistively Shunted Junction (RSJ) model. I-V characteristics (with and without microwaves) can be fit assuming an effective temperature approximately 15 K above the bath temperature. We have also investigated in detail structures in the I-V characteristics in the absence of microwaves. We show experimentally that phase-slip centers are induced at weak superconducting positions along the bridge when the S-N boundary of an expanding hot spot reaches within a thermal healing distance. The critical current of the phase-slip center thus formed exhibits a temperature dependence (1-T/T c )1/2instead of the usual mean field result (1-T/T c )3/2.