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Microwave Radiation (microwave + radiation)
Selected AbstractsCatalytic and Heating Behavior of Nanoscaled Perovskites under Microwave RadiationCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 7 2008T. Krech Abstract Perovskite powders of the types La0.5Ca0.5AlyM1,yO3,, (y = 0,0.8), M = Fe, Cr, Mn, Co and LaxSr1,xMnyCo1,y (x = 0.5,1, y = 0,1) were prepared via a sol-gel route according to the modified Pechini method. Incineration of the resins was performed before final sintering at 1000,°C for 6,h. The phase composition of the samples was established by X-ray powder diffraction analysis, and the lattice parameters were calculated using Rietveld analysis. The shape and size of the particles were determined via scanning electron microscopy and the specific surface area of the powder perovskites was established by the BET method. The principal particles were ca. 100,nm in size and formed agglomerates larger than 1.0,,m. The composition of the perovskites was established by EDX analysis. Following this, the catalytic behavior was tested by means of total oxidation of propane. The catalytic performance was measured at atmospheric pressure with 3,g of catalyst in a fixed-bed quartz reactor (i.d. = 18,mm) under thermal-assisted and microwave-assisted conditions. Initial results show a strong dependence of the catalytic and heating behavior on the nature of the M-atom and its number of unpaired d-electrons as well as on the particle size and its specific surface area. No significant difference in the results could be detected from comparison of the two heating methods. [source] Microwave-assisted Boc-solid phase peptide synthesis of cyclic cysteine-rich peptidesJOURNAL OF PEPTIDE SCIENCE, Issue 6 2008Abstract In this study we describe the first protocols for the synthesis of cystine-rich peptides in the presence of microwave radiation with Boc-solid phase peptide synthesis (SPPS). This method is exemplified for macrocyclic peptides known as cyclotides, which comprise ,30 amino acids and incorporate a cystine knot arrangement of their three disulfide bonds. However, the method is broadly applicable for a wide range of peptides using Boc-SPPS, especially for SPPS of large peptides via native chemical ligation. Microwave radiation produces peptides in high yield and with high purity, and we were able to reduce the time for the assembly of ,30 mer peptide chains to an overnight reaction in the automated microwave-assisted synthesis. Copyright © 2007 European Peptide Society and John Wiley & Sons, Ltd. [source] Spin-lattice relaxation of spin-½ nuclei in solids containing diluted paramagnetic impurity centers.CONCEPTS IN MAGNETIC RESONANCE, Issue 1 2003Abstract Dynamic nuclear polarization of nuclear spins via the solid-state and thermal mixing effects is discussed. Continuous-wave S- and X-band microwave radiation have been employed to measure 13C signal enhancements and polarization times for 13C nuclei in a natural type Ib diamond as a function of magnetic field. It was found that thermal mixing plays an important role in the 13C signal enhancement because the central electron spin resonance (ESR) line width HL , H0,C/,e, resulting in flip-flip and flip-flop forbidden transitions taking place simultaneously. On the other hand, the 13C spin-lattice relaxation rate is determined to a large extent by the solid-state effect (forbidden transitions). 13C polarization rates have also been measured for a suite of natural diamonds. It is shown that the polarization rate is proportional to the paramagnetic impurity concentration, in agreement with the theory. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson 19A: 36,43, 2003. [source] Analytical characterization of PEG polymers by MEKCELECTROPHORESIS, Issue 4 2010María R. Plata Abstract Characterization of PEGs with average molecular masses of up to 2000 has been achieved using MEKC with UV detection. A rapid derivatization procedure with phenyl isocyanate using microwave radiation, in order to introduce chromophore groups in PEGs, has been developed involving a reaction time of 60,s. Different optimized conditions in accordance with the molecular weight have been studied to obtain the oligomer separation. The weight-average molecular mass the number-average molecular mass and the degree of polydispersity (molecular mass distribution) were calculated for the different PEGs obtaining similar results with those certified for standards. A good precision was obtained for characterizing the different oligomers. Ethylene glycol was used as the internal standard for the analysis of low-molecular-weight PEGs. The developed method was satisfactorily applied to the characterization of these polymers in several real samples, such as lubricant eye drops, toothpaste, tap water and eye make-up remover. [source] The Selective Heating of Iron Nanoparticles in a Single-Mode Microwave for the Patterned Growths of Carbon Nanofibers and NanotubesADVANCED FUNCTIONAL MATERIALS, Issue 8 2009Tamara Druzhinina Abstract The fast and cheap synthesis of carbon nanotubes is addressed in a large number of recent publications. At the same time, microwave-assisted synthesis has also gained interest. Besides the fact that reaction kinetics can be positively influenced by the use of microwave irradiation and advanced reaction conditions can be applied, absorption of microwave radiation depends on the material properties, thus resulting in a selective heating mechanism. The selective heating process allows for locally created temperatures high enough to promote the growth of carbon nanofibers and nanotubes on patterned iron catalyst layers. The resulting fibers are micrometers long, and can be synthesized in short time scales of a few minutes, yielding dense films of carbon fibers with uniform height. Here, the selective heating of surface bound iron nanoparticles is investigated in more detail, and experimental evidence for this effect is provided by utilizing a self-assembled monolayer of n -octadecyltrichlorosilane, which acts as a sensitive indicator for locally elevated temperatures. Special emphasis is placed on the development of an improved and controllable experimental setup that permits the safe and fast fabrication of the desired carbon objects. [source] Microwave-Assisted Synthesis of Nanocrystalline MgO and Its Use as a BacteriocideADVANCED FUNCTIONAL MATERIALS, Issue 10 2005S. Makhluf Abstract Nanocrystalline particles of MgO were synthesized using microwave radiation in an ethylene glycol solution. The antibacterial activities of the MgO nanoparticles were tested by treating Escherichia coli (Gram negative) and Staphylococcus aureus (Gram positive) cultures with 1,mg,mL,1 of the nanoparticles. We have examined the importance of the size effect, pH, and the form of the active MgO species as a bactericidal agent. A clear size dependence of the nanoparticles is observed where the amount of eradicated bacteria was strongly dependent on the particle size. [source] Synthesis of Core/Shell Colloidal Magnetic Zeolite Microspheres for the Immobilization of TrypsinADVANCED MATERIALS, Issue 13 2009Yonghui Deng Magnetic zeolite microspheres are synthesized by combining sol-gel synthesis and vapor-phase transport. The microspheres, which have magnetite cores and crystalline zeolite shells (see figure), exhibit super-paramagnetism and a high adsorption capacity for trypsin. Trypsin-adsorbed microspheres digest proteins very efficiently (in only 15,s) in the presence of microwave radiation. [source] Ink-jet Printing and Microwave Sintering of Conductive Silver Tracks,ADVANCED MATERIALS, Issue 16 2006J. Perelaer Conductive silver tracks on a polyimide substrate (see figure) are prepared by using microwave radiation to sinter silver nanoparticles printed on the substrate. This method shortens the necessary sintering time dramatically and is independent of the substrate used. Since the polymer substrate is virtually transparent to microwave radiation, a negligible amount of energy is absorbed by the substrate, whereas the conducting silver nanoparticles, with a high dielectric loss factor, strongly absorb the microwaves. [source] A microwave-assisted process for coating polymer and glass surfaces with semiconducting ZnO submicron particlesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2009Alexander Irzh Abstract A new method for coating glass slides with ZnO particles with an average size of 200 nm is proposed in the current article. The coating was performed under microwave radiation. Two main morphologies are found for the ZnO crystals that are deposited on glass slides. The first morphology is that of a very dense coating of ZnO hexagonal rods growing perpendicular to the glass surface. The second is the growth of ZnO flower-like particles. In addition to coating the glass by ZnO particles, we also report on coating other polymers [poly(methyl methacrylate) plate, polycarbonate beads, Nylon 6,6 beads, and polypropylene beads) by ZnO. The morphology obtained for ZnO coated on polymers is different from that detected for coating ZnO on glass. The unorganized coating of ZnO rods on polymers has been observed. The coated glass slides were characterized by X-ray diffraction, volumetric titration, EDS, scanning electron microscope, and optical measurements (DRS and transmittance spectroscopy). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Biotransformation of benzaldehyde to L -phenylacetylcarbinol (L -PAC) by Torulaspora delbrueckii and conversion to ephedrine by microwave radiationJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 2 2002Vilas B Shukla Abstract In a 5,dm3 stirred tank reactor, bioconversion of 30,g benzaldehyde by cells of Torulaspora delbrueckii yielded 22.9,g of pure L -phenylacetylcarbinol (L -PAC). Facile functional group transformation of 4.5,g of L -PAC to 2-(methylimino)-1-phenyl-1-propanol by exposure to microwave irradiation for 9,min resulted in 2.48,g of product. Conversion of 4.8,g of 2-(methylimino)-1-phenyl-1-propanol to 3.11,g of ephedrine was achieved by exposure to microwaves in a reaction time of 10,min. The identity of all the products was confirmed by 1H NMR and FT-IR analysis. © 2002 Society of Chemical Industry [source] FREE-SPACE MICROWAVE MEASUREMENT of LOW MOISTURE CONTENT IN POWDERED FOODSJOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 1 2000RAM M. NARAYANAN A free-space microwave transmission technique has been developed and tested for rapid inline noninvasive measurement of the moisture content of various types of food powders. the basis of this technique is the relation between the attenuation of X-band microwave radiation through a sample of the food powder to its moisture content by weight. Since food powders generally lose their utility and desirable properties, such as flowability and resistance to spoilage, at lower levels of moisture content, typically 3,7%, special techniques must be developed in order to accurately characterize the moisture content at these low levels. One such technique is to use frequency averaging to enhance the accuracy of the measurements to avoid multiple reflection effects prevalent in low-loss low-moisture attenuation measurements. This technique was implemented in the moisture content estimation. Overall accuracies in moisture content estimation are generally less than 1%, although in some cases, accuracies are in the vicinity of 5%. [source] Preparation of 5-nitro-2-amino[b]thiophenes and 1-(2-amino-5-nitrophenyl)ethanones via microwave irradiationJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 4 2009Afsha Rais 1-(2-Chloro-5-nitrophenyl)ethanone) reacts with various amines in the presence of sulfur under microwave radiation to give the corresponding 2-aminobenzo[b]-thiophenes 3a,f in good yields. The yields of 3a,f are vastly superior to those obtained using conventional heating. Additionally, 1-(2-amino-5-nitrophenyl)ethanones 4a,f were also obtained. A mechanism is proposed in which 2-amino thiophenes 3a,f are formed by a SNAr mechanism involving an intramolecular addition of sulfur of the intermediate thioamide to the 2-substituted carbon to give a Meisenheimer complex, which collapses to 2-aminothiophenes 3a,f, and 2-amino ketones (4a,f) are formed by a parallel pathway involving nucleophilic addition amine to the 2-chloro position of 1 to form a Meisensheimer complex, which collapses to the amino ethanones. J. Heterocyclic Chem., (2009). [source] The effect of low-power microwaves on the growth of bacterial populations in a plug flow reactorAICHE JOURNAL, Issue 5 2010Renzo Carta Abstract A plug flow reactor (PFR) which permits the growth of bacteria in a microwave environment is described. The apparatus is used to analyse the effect of microwave radiation at the frequency of 2.45 GHz and at 37°C on the growth rate of three bacterial species: Bacillus clausii, Pseudomonas aeruginosa, and Staphylococcus aureus. The growth constant is determined for reacting mixtures irradiated with microwaves of different powers ranging from 0 to 400 mW. Analyses show that (a) the apparatus is able to perform the experimental runs maintaining an aseptic environment; (b) under the microwave power levels examined in the present study, no effects are detected for the Bacillus clausii and Pseudomonas aeruginosa species, while for the Staphylococcus aureus species, a few small effects are found (a minimum value of the growth constant at 200 mW and an increase of the constant between 200 and 400 mW). © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Microwave-assisted Boc-solid phase peptide synthesis of cyclic cysteine-rich peptidesJOURNAL OF PEPTIDE SCIENCE, Issue 6 2008Abstract In this study we describe the first protocols for the synthesis of cystine-rich peptides in the presence of microwave radiation with Boc-solid phase peptide synthesis (SPPS). This method is exemplified for macrocyclic peptides known as cyclotides, which comprise ,30 amino acids and incorporate a cystine knot arrangement of their three disulfide bonds. However, the method is broadly applicable for a wide range of peptides using Boc-SPPS, especially for SPPS of large peptides via native chemical ligation. Microwave radiation produces peptides in high yield and with high purity, and we were able to reduce the time for the assembly of ,30 mer peptide chains to an overnight reaction in the automated microwave-assisted synthesis. Copyright © 2007 European Peptide Society and John Wiley & Sons, Ltd. [source] Microwave-Assisted Synthesis of Fine Particle Oxides Employing Wet Redox MixturesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2002Solomon Sundar Manoharan Interaction of electromagnetic radiation with a physical mixture of metal nitrates and amides/hydrazides is observed to initiate high-temperature reactions, useful for realizing several high-temperature ceramic materials. A judicious choice of such redox mixtures undergoes exothermic reactions when they couple with microwave radiation. The coupling of electromagnetic radiation with metal salts and amides/hydrazides depends on the dielectric properties of the individual components in the reaction mixture. The approach has been used to prepare ,-Fe2O3, Fe3O4, MgCr2O4, ,-CaCr2O4, and La0.7Ba0.3MnO3. [source] Electrophoretic patterns of microwaved and ,-irradiated beef liver proteinsJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 10 2001S Farag Abstract The effects of ,-irradiation treatments (2.5, 5 and 10,kGy) and microwaves generated from an oven at low and defrost power settings for 0.5, 1 and 2,min on the total proteins and protein patterns of beef liver immediately after treatment and during frozen storage (,18,°C) for different periods were studied. Chemical analyses indicated that the protein content of beef liver was reduced after exposure to ,-radiation or microwaves and also during frozen storage. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) was used to illustrate the changes in protein bands of different molecular weights and their percentages before and after exposure to gamma and microwave radiation. The main effect of ,-radiation on the protein patterns of beef liver was the disappearance of some high-molecular-weight protein bands and the development of other bands characterised by moderate and low molecular weights. This finding indicates the degradation of beef liver proteins by ,-irradiation. In contrast, microwave treatment caused an increase in the levels of high-molecular-weight protein bands with a concomitant decrease in low-molecular-weight protein bands. This phenomenon demonstrates the polymerisation of low-molecular-weight proteins under the influence of microwaves. © 2001 Society of Chemical Industry [source] Characterization of oil sands naphthenic acids treated with ultraviolet and microwave radiation by negative ion electrospray Fourier transform ion cyclotron resonance mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 21 2010John V. Headley Naphthenic acids (NAs) are concentrated in oil sand process water (OSPW) as a result of caustic oil sands extraction processes. There is considerable interest in methods for treatment of NAs in OSPW. Earlier work has shown that the combination of ultraviolet (UV) and microwave treatments in the laboratory was effective in reducing the concentration of classical NAs. Here we apply Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to further characterize NAs treated with (a) UV (254,nm) in the presence of TiO2 catalyst; and/or (b) microwave irradiation (2.45,GHz). FT-ICR MS was used to characterize the NA fraction before and after treatment. Acidic oxygen-containing classes were most abundant in all samples whereas other heteroatomic classes were least abundant or not present in some samples. For example, the SO2 -containing species were absent in UV- or combined UV- and microwave-treated samples. The O2 class was dominant in all samples, indicative of NAs. However, samples treated with UV and microwave radiation have a lower relative abundance of other heteroatomic classes. We observed O2, S1O2, O3, S1O3, O4, O5, and O6 classes, whereas the species with relatively high On content, namely, the O3, O5, and O6 classes, were present only in UV- and microwave-treated samples. The relatively high On content is consistent with oxidation of the parent acids in treated samples. There may thus be potential implications for environmental forensics. For example, the monitoring of the ratio of SO2:O2 or tracking the relative abundances of O2, O3, O4, O5, and O6 classes may provide insights for distinguishing naturally derived oil sands components from those that are process-related in aquatic environments. Copyright © 2010 John Wiley & Sons, Ltd. [source] Low-intensity microwave irradiation does not substantially alter gene expression in late larval and adult Caenorhabditis elegansBIOELECTROMAGNETICS, Issue 8 2009Adam S. Dawe Abstract Reports that low-intensity microwave radiation induces heat-shock reporter gene expression in the nematode, Caenorhabditis elegans, have recently been reinterpreted as a subtle thermal effect caused by slight heating. This study used a microwave exposure system (1.0,GHz, 0.5,W power input; SAR 0.9,3,mW,kg,1 for 6-well plates) that minimises temperature differentials between sham and exposed conditions (,0.1 °C). Parallel measurement and simulation studies of SAR distribution within this exposure system are presented. We compared five Affymetrix gene arrays of pooled triplicate RNA populations from sham-exposed L4/adult worms against five gene arrays of pooled RNA from microwave-exposed worms (taken from the same source population in each run). No genes showed consistent expression changes across all five comparisons, and all expression changes appeared modest after normalisation (,40% up- or down-regulated). The number of statistically significant differences in gene expression (846) was less than the false-positive rate expected by chance (1131). We conclude that the pattern of gene expression in L4/adult C. elegans is substantially unaffected by low-intensity microwave radiation; the minor changes observed in this study could well be false positives. As a positive control, we compared RNA samples from N2 worms subjected to a mild heat-shock treatment (30 °C) against controls at 26 °C (two gene arrays per condition). As expected, heat-shock genes are strongly up-regulated at 30 °C, particularly an hsp -70 family member (C12C8.1) and hsp -16.2. Under these heat-shock conditions, we confirmed that an hsp -16.2::GFP transgene was strongly up-regulated, whereas two non-heat-inducible transgenes (daf- 16::GFP; cyp -34A9::GFP) showed little change in expression. Bioelectromagnetics 30:602,612, 2009. © 2009 Wiley-Liss, Inc. [source] Effects of 100 GHz radiation on alkaline phosphatase activity and antigen,antibody interaction,BIOELECTROMAGNETICS, Issue 3 2009A. Homenko Abstract Equipment that generates microwave radiation (MWR) spanning the frequency range of 300 MHz,100 GHz is becoming more common. While MWR lacks sufficient energy to break chemical bonds, the disagreement as to whether MWR exposure is detrimental to cellular dysfunction may be difficult to clarify using complex systems such as whole animals, cells, or cell extracts. Recently, the high frequency range of terahertz (THz) radiation has been explored and sources of radiation and its detectors have been developed. THz radiation is associated with the frequency interval from 100 GHz to 20 THz and constitutes the next frontier in imaging science and technology. In the present study, we investigated the effect of radiation in the low frequency THz range (100 GHz) on two defined molecular interactions. First, the interaction of soluble or immobilized calf alkaline phosphatase with the substrate p -nitrophenylphosphate and second, the interaction between an antibody (mouse monoclonal anti-DNP) and its antigen (DNP). Irradiation of enzyme either prior to addition of substrate or during the enzymatic reaction resulted in small but significant reductions in enzyme activity. These differences were not observed if the enzyme had previously been immobilized onto plastic microwells. Exposure of immobilized antigen to radiation did not influence the ability of the antigen to interact with antibody. However, irradiation appeared to decrease the stability of previously formed antigen,antibody complexes. Our data suggest that 100 GHz radiation can induce small but statistically significant alterations in the characteristics of these two types of biomolecular interactions. Bioelectromagnetics 30:167,175, 2009. © 2008 Wiley-Liss, Inc. [source] Effect of low frequency modulated microwave exposure on human EEG: Individual sensitivityBIOELECTROMAGNETICS, Issue 7 2008Hiie Hinrikus Abstract The aim of this study was to evaluate the effect of modulated microwave exposure on human EEG of individual subjects. The experiments were carried out on four different groups of healthy volunteers. The 450 MHz microwave radiation modulated at 7 Hz (first group, 19 subjects), 14 and 21 Hz (second group, 13 subjects), 40 and 70 Hz (third group, 15 subjects), 217 and 1000 Hz (fourth group, 19 subjects) frequencies was applied. The field power density at the scalp was 0.16 mW/cm2. The calculated spatial peak SAR averaged over 1 g was 0.303 W/kg. Ten cycles of the exposure (1 min off and 1 min on) at fixed modulation frequencies were applied. All subjects completed the experimental protocols with exposure and sham. The exposed and sham-exposed subjects were randomly assigned. A computer also randomly assigned the succession of modulation frequencies. Our results showed that microwave exposure increased the EEG energy. Relative changes in the EEG beta1 power in P3-P4 channels were selected for evaluation of individual sensitivity. The rate of subjects significantly affected is similar in all groups except for the 1000 Hz group: in first group 3 subjects (16%) at 7 Hz modulation; in second group 4 subjects (31%) at 14 Hz modulation and 3 subjects (23%) at 21 Hz modulation; in third group 3 subjects (20%) at 40 Hz and 2 subjects (13%) at 70 Hz modulation; in fourth group 3 subjects (16%) at 217 Hz and 0 subjects at 1000 Hz modulation frequency. Bioelectromagnetics 29:527,538, 2008. © 2008 Wiley-Liss, Inc. [source] Microwave-based alkali pretreatment of switchgrass and coastal bermudagrass for bioethanol productionBIOTECHNOLOGY PROGRESS, Issue 3 2010Deepak R. Keshwani Abstract Switchgrass and coastal bermudagrass are promising lignocellulosic feedstocks for bioethanol production. However, pretreatment of lignocelluloses is required to improve production of fermentable sugars from enzymatic hydrolysis. Microwave-based alkali pretreatment of switchgrass and coastal bermudagrass was investigated in this study. Pretreatments were carried out by immersing the biomass in dilute alkali reagents and exposing the slurry to microwave radiation at 250 W for residence times ranging from 5 to 20 min. Simons' stain method was used to quantify changes in biomass porosity as a result of the pretreatment. Pretreatments were evaluated based on yields of total reducing sugars, glucose, and xylose. An evaluation of different alkalis identified sodium hydroxide as the most effective alkali reagent for microwave-based pretreatment of switchgrass and coastal bermudagrass. 82% glucose and 63% xylose yields were achieved for switchgrass and 87% glucose and 59% xylose yields were achieved for coastal bermudagrass following enzymatic hydrolysis of biomass pretreated under optimal conditions. Dielectric properties for dilute sodium hydroxide solutions were measured and compared with solid losses, lignin reduction, and reducing sugar levels in hydrolyzates. Results indicate that dielectric loss tangent of alkali solutions is a potential indicator of the severity of microwave-based pretreatments. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] | |||||||||||||||||||||||||