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PubMed2006

Microwave-assisted growth and characterization of water-dispersed CdTe/CdS core-shell nanocrystals with high photoluminescence.

A novel microwave-assisted method of growth of high-quality CdTe/CdS core-shell nanocrystals in the aqueous phase is presented in this paper. The photoluminescence quantum yield (PLQY) is greatly enhanced by epitaxial growth of the CdS shell. Under optimum conditions, the PLQY of as-prepared nanocrystals reaches as high as 75% without any post-treatment. Furthermore, these investigations demonstrate that microwave irradiation is tremendously useful for fast epitaxial growth of nanocrystals due to its special characteristics. As a result, the microwave synthesis is sufficiently time-economizing (only five minutes are required) to obtain optimum amounts of CdTe/CdS core-shell nanocrystals in comparison to the conventional illumination method (several days are required). Therefore, this current research not only provides a rapid microwave synthesis for producing highly fluorescent CdTe/CdS core-shell nanocrystals, but also it presents some advantages of the microwave synthesis in comparison to the illumination method.

Journal Article↗
PubMed2006

Microwave spectra, ab initio calculations, and r0 structural parameters for (methylamino)thiophosphoryl difluoride.

The microwave spectra of (methylamino)thiophosphoryl difluoride, CH(3)NHP(=S)F(2), and two deuterated species, CH(3)NDP(=S)F(2) and CD(3)NHP(=S)F(2), have been investigated in the region from 26.5 to 39.0 GHz. The rotational constants of the ground vibrational state have been determined and have been shown to be only consistent with the trans conformer (CH(3) group antiperiplanar to the P=S bond) with C(s) symmetry. The a-type R branch transitions have been assigned for the trans conformer for the three isotopomers on the basis of the rigid rotor model. Near-trans and near-cis forms without molecular planes of symmetry are predicted by all ab initio calculations with the near-trans form being more stable. However, the double-well potentials governing the interchange between the two enantiomeric near-trans as well as the two near-cis forms are too shallow to accommodate the zero-point energies of the nu(24) asymmetric torsion. Thus, the trans conformation with C(s) symmetry may be more accurate in explaining the microwave experimental data. The "adjusted" r(0) structural parameters have been obtained by systematically adjusting the ab initio MP2(full)/6-311+G(d,p) structure of the trans conformer with C(s) symmetry to fit the microwave rotational constants. The determined heavy atom distances are r(C-N) = 1.459(5), r(P-N) = 1.621(5), r(P=S) = 1.879(5), and r(P-F) = 1.550(5) A, and the heavy atom angles are angleCNP = 124.7(5) degrees , angleNPS = 118.3(5) degrees , angleNPF = 103.2(5) degrees , angleFPS = 117.0(5) degrees , and angleFPF = 94.6(5) degrees . The adjusted r(0) parameters have also been obtained for aminodifluorophosphine, H(2)NPF(2), with a slightly pyramidal -PNH(2) moiety. The results indicate that the previously reported short distance of 0.981(5) A for the N-H(o)(outer) bond from the microwave study is too short, and the adjusted r(0) value of 1.007(3) A is obtained from the combined data. Adjusted r(0) parameters are also reported for (dimethylamino)difluorophosphine, (CH(3))(2)NPF(2), with C(s) symmetry with the PNC(2) portion of the molecule being planar. The previously reported C-H distances from the electron diffraction study are too long, and the anglePNC(i) and angleC(o)NC(i) angles are also found to be in error. These results provide a reasonable explanation why the microwave and electron diffraction results differ for the structures of these latter two molecules.

Journal Article↗
PubMed2000

A flat Universe from high-resolution maps of the cosmic microwave background radiation

The blackbody radiation left over from the Big Bang has been transformed by the expansion of the Universe into the nearly isotropic 2.73 K cosmic microwave background. Tiny inhomogeneities in the early Universe left their imprint on the microwave background in the form of small anisotropies in its temperature. These anisotropies contain information about basic cosmological parameters, particularly the total energy density and curvature of the Universe. Here we report the first images of resolved structure in the microwave background anisotropies over a significant part of the sky. Maps at four frequencies clearly distinguish the microwave background from foreground emission. We compute the angular power spectrum of the microwave background, and find a peak at Legendre multipole Ipeak = (197 +/- 6), with an amplitude delta T200 = (69 +/- 8) microK. This is consistent with that expected for cold dark matter models in a flat (euclidean) Universe, as favoured by standard inflationary models.

Journal Article↗
PubMed1991

Near-classical noise enhancement of microwave ionization of Rydberg atoms.

The ionization of the highly excited hydrogen atom in a strong external microwave field is a classically chaotic, near-classical quantum system for microwave frequencies somewhat below the initial Kepler electron orbit frequency. The addition of microwave noise is found to reduce the sinewave microwave field needed for ionization, modifying the near-classical fast process responsible for the microwave energy absorption. A classical numerical calculation based upon a many-frequency model of the noise qualitatively reproduces the observed noise enhancement.

Journal Article↗
PubMed2002

Drying phenomenon of Moroccan natural phosphates under microwave irradiation. Part I: Thermal and kinetic aspects.

In this paper, the use of microwave energy in a drying problem is examined. The purpose of this work is the investigation of the effect of incident microwave power to a material during drying and in particular the research of the experimental conditions which can be used to accelerate the drying phenomenon in order to save energy in the industrial processes. We describe, in the first instance, the experimental apparatus used and the results of kinetic and thermal aspects of drying induced by microwave heating. These results lead to the role of different parameters (microwave power, initial sample mass and diameter of the reactor) on the kinetic and the thermal aspects of the drying. In the second instance, the experimental results are presented and discussed taking into account the dielectric proprieties of the material, the literature and the use of the heterogeneous kinetic models. These studies point out important kinetic and thermal aspects allowing a better understanding of drying under microwave irradiation.

Journal Article↗
PubMed2006

Negative temperature programming using microwave open tubular gas chromatography.

A microwave gas chromatography (GC) column oven is engineered to generate a uniform microwave field around an open tubular column with the elimination of cold spots, which are common in a domestic microwave oven. Short cool-down time in microwave heating makes it possible to employ negative temperature programming for the enhanced separation of compounds during the process. The feasibility of negative temperature programming in microwave GC is investigated for the analysis and quantitation of four different pairs of nonvolatile and volatile compounds. The influence of intermediate column cooling rate, holding time in the cooling ramp, and reheating rate after the cooling ramp for enhanced resolution are investigated. The results obtained from negative temperature programming are compared with those from positive temperature programming. Negative temperature programming affords greater resolution of some critical pairs of analytes.

Journal Article↗
PubMed2007

Transurethral microwave thermotherapy: from evidence-based medicine to clinical practice.

PURPOSE OF REVIEW: The aim of this article is to provide new clinical data on transurethral microwave thermotherapy, evaluate it in the perspective of evidence-based guidelines and daily practice and investigate the driving forces that determine the current position of thermotherapy for the management of benign prostatic obstruction. RECENT FINDINGS: Recent studies have provided significant evidence regarding the efficacy, safety and durability of thermotherapy. Updated evidence-based clinical guidelines on the management of patients with benign prostatic obstruction have been made available. Surveys have evaluated the acceptance of transurethral microwave thermotherapy from the urological community. In addition, several studies have made major contributions to our knowledge of the translation of evidence to daily practice. SUMMARY: The range of therapeutic options for benign prostatic obstruction continues to widen creating the need for clarity in selection and application of these treatments. High-quality data on transurethral microwave thermotherapy have been published and integrated into clinical guidelines. Considerations on the implementation of guidelines to clinical practice, emergence of new treatments, shift of benign prostatic obstruction therapy, economics and the increasing need to treat patients with different clinical profile during the last decade seem to affect the position of transurethral microwave thermotherapy in the armamentarium of a urological centre. Into this frame, transurethral microwave thermotherapy tailored to selective cases seems to remain an attractive option.

Evidence-Based Medicine↗
PubMed2004

Experimental simulation of quantum graphs by microwave networks.

We present the results of experimental and theoretical study of irregular, tetrahedral microwave networks consisting of coaxial cables (annular waveguides) connected by T joints. The spectra of the networks were measured in the frequency range 0.0001-16 GHz in order to obtain their statistical properties such as the integrated nearest neighbor spacing distribution and the spectral rigidity Delta(3) (L). The comparison of our experimental and theoretical results shows that microwave networks can simulate quantum graphs with time reversal symmetry. In particular, we use the spectra of the microwave networks to study the periodic orbits of the simulated quantum graphs. We also present experimental study of directional microwave networks consisting of coaxial cables and Faraday isolators for which the time reversal symmetry is broken. In this case our experimental results indicate that spectral statistics of directional microwave networks deviate from predictions of Gaussian orthogonal ensembles in random matrix theory approaching, especially for small eigenfrequency spacing s, results for Gaussian unitary ensembles. Experimental results are supported by the theoretical analysis of directional graphs.

Journal Article↗
PubMed2004

Propagation characteristics and guiding of a high-power microwave in plasma waveguide.

The propagation characteristics of a high-power microwave [electromagnetic (em) wave] in a plasma waveguide are reported. The plasma waveguide is formed by expanding plasmas via the ponderomotive force of the high-power microwave and the microwave pulse remains trapped within the plasma waveguide and is guided in it. With the increase of the incident microwave power, the width of the plasma waveguide increases and the half width of the radial electric field distribution decreases. This shows that the em wave modifies the refractive index of the plasma waveguide area. For a plasma waveguide with narrower width, the microwave propagates along the plasma waveguide at the fundamental TE mode, while as the waveguide width increases the higher mode component starts appearing. Analytical treatment to the propagation of the electromagnetic wave in a dielectric waveguide having a step-index profile and the numerical calculations for the radial distribution of the electric field show fairly good agreement with the results observed in the present experiments.

Journal Article↗
PubMed1997

p53 gene product expression in resected non-small cell carcinoma of the lung, with studies of concurrent cytological preparations and microwave antigen retrieval.

AIM: To document the frequency and extent of p53 gene product expression in paraffin sections of resected non-small cell carcinoma of the lung and in cytological preparations of the same tumours; to determine the effect of microwave antigen retrieval on antigen detection. METHODS: Representative paraffin sections of 50 non-small cell carcinomas were stained with an antibody to p53 gene product (DO-7) both with and without prior microwave antigen retrieval. Cytoblocks and cell smears obtained from 19 cases were similarly stained. RESULTS: Using a histochemical scoring system (0-300) which takes into account staining intensity and extent, 78% (n = 39) of microwave pretreated paraffin sections and 52% (n = 26) of non-pretreated sections scored between 5 and 300; p = 0.001; 56% (n = 28) of microwave pretreated sections and only 2% (n = 1) of non-pretreated sections scored between 100 and 300 (p = 0.0001); 75% of direct smears of tumours and 80% of cytoblocks stained similarly to the paraffin sections of the resected specimens. No smears or cytoblocks stained positively when the sections of the resected specimen were negative. CONCLUSIONS: As up to 78% of non-small cell lung carcinomas overexpress p53 gene product, this may prove to be a valuable diagnostic method in biopsy or cytological material when the morphological diagnosis is uncertain. Microwave antigen retrieval is effective on formalin fixed tissue.

Adenocarcinoma↗
PubMed2004

Frequency shifting of microwave signals by use of a general temporal self-imaging (Talbot) effect in optical fibers.

A simple and practical microwave frequency-shifting technique based on a general temporal self-imaging (GTSI) effect in optical fiber is proposed, formulated, and experimentally demonstrated. The proposed technique can be applied to an arbitrary periodic microwave signal (e.g., a microwave tone) and provides unparalleled design flexibility to increase the frequency of the input microwave signal up to the desired value (limited only by the photodetector's bandwidth). For instance, we demonstrate frequency upshifting of microwave tones from approximately 10 to approximately 50 GHz and from approximately 40 to approximately 354 GHz. These results also represent what is to the authors' knowledge the first experimental observation of GTSI phenomena.

Journal Article↗
PubMed1984

Stability of cephapirin sodium admixtures after freezing and conventional or microwave thaw techniques.

The freeze-microwave thaw technique has important advantages compared with conventional piggyback delivery systems. A requirement for the implementation of this technique, however, is the documentation of antibiotic stability following freezing and microwave thawing. The purpose of this study was to assess the stability of a commonly used cephalosporin, cephapirin sodium, following freezing and conventional or microwave thawing. This data was not previously available. Cephapirin sodium was admixed with either 5% dextrose injection or 0.9% sodium chloride injection in polyvinylchloride minibags at concentrations of 10 and 40 mg/ml and then frozen for 14 days. Admixtures were then thawed conventionally or by microwave heating. Cephapirin concentrations were determined spectrophotometrically after reconstitution, immediately after thawing, and 6, 12, and 24 hours after thawing. No significant differences in admixture potency after reconstitution, immediately after thawing, or at 6, 12, and 24 hours after thawing were observed when thaw techniques were compared. All admixtures retained at least 90% of labeled content regardless of thaw technique, type of diluent, or initial concentration. In addition, all admixtures retained at least 90% potency 24 hours after thawing when compared with the actual concentration determined immediately after reconstitution. The rate of cephapirin degradation was not influenced by thaw technique, type of diluent, or initial admixture concentration. The results of this study suggest that cephapirin sodium may be added to the list of drugs capable of withstanding freeze-microwave thaw treatment.

Cephalosporins↗
PubMed1996

Microwave absorption by magnetite: a possible mechanism for coupling nonthermal levels of radiation to biological systems.

The presence of trace amounts of biogenic magnetite (Fe3O4) in animal and human tissues and the observation that ferromagnetic particles are ubiquitous in laboratory materials (including tissue culture media) provide a physical mechanism through which microwave radiation might produce or appear to produce biological effects. Magnetite is an excellent absorber of microwave radiation at frequencies between 0.5 and 10.0 GHz through the process of ferromagnetic resonance, where the magnetic vector of the incident field causes precession of Bohr magnetons around the internal demagnetizing field of the crystal. Energy absorbed by this process is first transduced into acoustic vibrations at the microwave carrier frequency within the crystal lattice via the magnetoacoustic effect; then, the energy should be dissipated in cellular structures in close proximity to the magnetite crystals. Several possible methods for testing this hypothesis experimentally are discussed. Studies of microwave dosimetry at the cellular level should consider effects of biogenic magnetite.

Acoustics↗
PubMed1996

Preliminary report on treatment of bone tumors with microwave-induced hyperthermia.

Between July, 1992, and February, 1995, 62 patients with various bone tumors were treated with microwave-induced hyperthermia. The series had 47 cases of malignant tumors and 15 cases with benign tumors; most of the tumors occurred at or near knee joints (53/62 = 85.4%). The surgical procedure consisted of separating the tumorous segment from surrounding normal tissues with a safe margin, cooling the normal tissues (including the vital neurovascular bundle and the intrajoint structures) with a water circulation system while heating the tumor simultaneously with the microwave antenna array, and providing an adequate soft-tissue cover for the dead bone. The tumor core temperature and the surface temperature reached 108 and 65 degrees C, respectively. The duration of microwave irradiation was usually 40-50 minutes. Meanwhile, the temperature of the normal tissues was kept under 39 degrees C. The minimal and maximal periods of clinical observation were 3 months and 36 months, respectively, and the mean follow-up period was 17 months. The 62 cases were evaluated from both oncological and orthopedic points of view. Five cases had local recurrence and required amputation. The 57 other cases had excellent local control. Six malignancy cases died of lung metastasis during a period of 1-2 years. Pathological fracture occurred at devitalized bone in five cases. In most of the cases, the knee joints functioned well, were stable and painless, and had almost full range of motion. Single-photon emission-computed tomography study in 16 cases revealed that revascularization of the devitalized tumorous bone segment could be accomplished in 1 year or more. These results show that the use of microwave hyperthermia for the treatment of bone tumors can be considered to be a definitive operation procedure that is safe and is well tolerated by patients. The oncological and orthopedic results are very encouraging.

Adolescent↗
PubMed1999

Pulsed microwave induced light, sound, and electrical discharge enhanced by a biopolymer.

Intense flashes of light were observed in sodium bicarbonate and hydrogen peroxide solutions when they were exposed to pulsed microwave radiation, and the response was greatly enhanced by a microwave-absorbing, biosynthesized polymer, diazoluminomelanin. A FPS-7B radar transmitter, operating at 1.25 GHz provided pulses of 5.73 +/- 0.09 micros in duration at 10.00 +/- 0.03 pulses/s with 2.07 +/- 0.08 MW forward power (mean +/- standard deviation), induced the effect but only when the appropriate chemical interaction was present. This phenomenon involves acoustic wave generation, bubble formation, pulsed luminescence, ionized gas ejection, and electrical discharge. The use of pulsed microwave radiation to generate highly focused energy deposition opens up the possibility of a variety of biomedical applications, including targeting killing of microbes or eukaryotic cells. The full range of microwave intensities and frequencies that induce these effects has yet to be explored and, therefore, the health and safety implications of generating the phenomena in living tissues remain an open question.

Absorption↗
PubMed1980

Microwave-induced local hyperthermia in combination with radiotherapy of human malignant tumors.

Since 1976, two groups of patients have been treated with local microwave hyperthermia immediately following ionizing radiation. Group A patients had measurable multiple lesions assigned radiotherapy only, microwave hyperthermia only, or combined treatment. Ionizing radiation in 200-600 rad fractions was used 2-5 times per week to a total of 1800-4200 rad in 5-14 fractions. Group B patients had combination treatment only, with radiation fractions of 200-600 rad 2-5 times per week to a total of 2000-4800 rad total in 6-20 fractions. Both groups received hyperthermia (42-44 C) 2-3 times per week, maximum ten sessions in four weeks. The 19 patients treated have had squamous cell carcinoma, adenocarcinoma, malignant melanoma, plasmacytoma, epithelioid sarcoma, and undifferentiated carcinoma. After more than 150 hyperthermia sessions, we find: (1) local hyperthermia with microwave alone or in combination with ionizing radiation can be used with excellent normal tissue tolerance provided local tissue temperatures are carefully monitored and controlled; (2) a higher level of heat induction in tumor tissue as compared to surrounding normal tissues; (3) repeated hyperthermia at 42-43.5 C for 45 minutes per session immediately following photon irradiation yields a favorable therapeutic result, occasionally dramatic. Local microwave hyperthermia in combination with radiotherapy offers the possibility of substantial impact on clinical cancer therapy, whether of curative or palliative intent.

Adolescent↗
PubMed2002

Effect of gamma-radiation and microwave heating on endosperm microstructure in relation to some technological properties of wheat grain.

Grains of the Polish winter wheat variety Begra were subject to gamma-radiation (60Co) within the dose range of 0.05-10 kGy and microwave treatment from 15 to 180 s, the latter resulting in a bulk grain temperature ranging from 28 to 98 degrees C. Both processes were responsible for marked structural changes of wheat kernel endosperm and were pronounced with increasing dose of ionizing radiation or with prolonged time of microwave treatment. Endosperm microstructures of wheat kernels treated with gamma-radiation ranging from 0.05 to 0.5 kGy did not differ from that of untreated ones. Only some changes in the structure of starch granules and proteins were observed at doses of 1, 5 and 10 kGy. Simultaneously at the doses of 5 and 10 kGy a statistically significant decrease of falling number, sodium dodecyl sulfate (SDS) sedimentation values, dough stability and energy were observed, while dough weakening progressed. Microwave treatment longer than 90 s caused marked changes in kernel endosperm structure. Some changes of proteins caused by denaturation created visible fibrils as well as high swelling and deformation of starch granules. This was followed by an increase in the falling number value, decrease in the estimated results of SDS sedimentation test, lowering of the percent of gluten washed out and of the dough energy, respectively. Also a significant decrease in bread quality expressed by volume and score was observed with increasing time of exposure to microwave.

Bread↗
PubMed2002

Application of intracellular microelectrophoresis to analysis of the influence of the low-level microwave radiation on electrokinetic properties of nuclei in human epithelial cells.

Intracellular microelectrophoresis was applied to investigate the electrokinetic properties of human buccal epithelium cell nuclei after exposure of cells to microwaves of wavelengths of 8 mm (f = 37.5 GHz) and 16 mm (f = 18.75 GHz) at a surface power density of 0.2 mW/cm(2). Irradiated or nonirradiated cells were suspended in a flat microelectrophoretic chamber and exposed to an electric field of 15 V/cm at a current flow of 0.1 mA. The cells, whose nuclei altered their intracellular location towards the anode of the externally applied electric field, were considered to have negatively charged nuclei. The percentage of cells with electrophoretically movable nuclei was determined as the value of electronegativity of cell nuclei (ENN). Microwaves induced changes of ENN during irradiation of 15-60 s. If cells of a donor had an elevated initial level of ENN, it decreased during irradiation. On the contrary, if cells of another donor had a low initial ENN level, irradiation induced ENN increase. No significant difference between the action of microwaves of wavelengths of 8 mm and 16 mm was found. However, microwave irradiation caused an increase in membrane permeability for the in vivo dye indigo Carmine in cells of all donors irrespectively of the initial levels they showed. This suggests that electrokinetic properties of nuclei in cells do not only depend on cell membrane permeability.

Cell Nucleus↗